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Perennial Flowers and Plants

The term perennial refers to non-woody plants that live and flower for three or more years. Some are short-lived and will last in the garden for only three to four years. Others will live and bring vibrant color to the garden for many years. Most perennials will die to the ground over winter and regrow from crowns or roots when warm spring weather arrives.

Perennials provide an advantage over annuals in that they do not need to be replanted every year. They also require very little in the way of fertilizer, and in some cases water inputs. A disadvantage is that many perennials do not flower over the entire summer. This can be overcome by planting many complementary species to ensure that at least some are in bloom at any given time. Many perennials are planted for their interesting form or beautiful foliage.

Perennial plants can be used to create interest in any landscape. They mix well with rocks, fences, hardscaping and other permanent landscape features. They are best used in places where they can establish a deep and healthy root system, such as in traditional beds, rock gardens or borders. Many perennials can thrive in situations that are problematic for other types of plants, making them good specimens for sloped areas, water conserving gardens, poor soils and native plantings.

In this section, you will be guided through information on selecting, planting and caring for perennial flower and foliage plants. Ornamental grasses and bulbs, although technically considered perennials are covered as separate topics due to their unique characteristics and management requirements.

Globe Thistle

Globe Thistle is an attractive tall perennial


Selection of the proper plant species and varieties will determine ultimate success with perennials. One critical characteristic is the ability to survive Idaho’s winters. Also, care must also be taken to choose plants that complement their surroundings and are suitable for the intended purpose. Perennials planted within a single bed should have similar growth and care requirements.

 

Perennials can be categorized into groups, based on growth characteristics or intended use, making selection easier. Useful groupings include plant dimensions, site conditions (e.g. tolerant of drought, moist, or shade conditions), bloom period, and attractiveness to birds and butterflies.

For additional information, including pictures, designed to provide assistance with selection of perennials, pursue the following links:

Leonard Perry, University of Vermont maintains an outstanding site that provides not only pictures of numerous perennial flowers, but also extensive information on adaptation, landscape uses, pest problems, and maintenance tips.

Heritage Perennials maintains an extensive searchable database of perennials, complete with pictures of many varieties.

Red Hot Poker

Red Hot Poker is a tall perennial that loves heat. Courtesy of FreeFoto.com

Tall Perennials

Tall plants can be used to hide foundations or other unattractive landscape features. They also make good backdrops for shorter perennials or annuals. Many tall perennials can be leggy or have sparse foliage, meaning they are at their best when planted with or behind shorter, denser plants. Tall perennials suitable for planting in Idaho include:

Common Name Scientific Name Regional Adaptation
Aster Aster spp. N, SW, SC, SE, HA
Bee Balm Monarda didyma N, SW, SC, SE
Blue False Indigo Baptisia australis N, SW, SC, SE, HA
Butterfly Weed Asclepias tuberose N, SW, SC, SE, HA
Cardinal Flower Lobelia cardinalis N, SW, SC, SE, HA
Chrysanthemum (tall varieties) Deudranthuna x grandiflora N, SW, SC, SE, HA
Columbine Aquilegia spp. N, SW, SC, SE, HA
Foxglove Digitalis purpurea N, SW, SC, SE
Gas Plant Dictamnus albus N, SW, SC, SE, HA
Globe Thistle Echinops ritro N, SW, SC, SE, HA
Gloriosa Daisy Rudbeckia x hybrida N, SW, SC, SE, HA
Goatsbeard Aruncus dioicus N, SW, SC, SE
Hollyhock Alcea rosea N, SW, SC, SE, HA
Japanese Anenome Anenome x hybrida N, SW, SC, SE, HA
Mullein Verbascum spp. SW, SC, SE
Obedient Plant Physostegia virginiana N, SW, SC, SE, HA
Orange Coneflower Rudbeckia fulgida var. sullivantii N, SW, SC, SE
Oriental Poppy Papaver orientalis N, SW, SC, SE, HA
Penstemon Penstemon spp. N, SW, SC, SE, HA
Peony Paeonia lactiflora N, SW, SC, SE, HA
Purple Coneflower Echinacea purpurea N, SW, SC, SE, HA
Red Hot Poker Kniphofia uvaria SW, SC
Red Valerian Centranthus ruber SW, SC
Russian Sage Perovskia atriplicifolia SW, SC
Sage Salvia officinalis N, SW, SC, SE, HA
Sneezeweed (Helen’s Flower) Helenium autumnales N, SW, SC, SE, HA
Yarrow Achillea spp. N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston). HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Forget-me-not

Forget-Me-Not has a sky blue flower

 

Short and Medium Perennials

These plants can be mixed with taller perennials and also used in rock gardens and borders. Medium-sized perennials suitable for use in Idaho include:

Common Name Scientific Name Regional Adaptation
Alumroot (Coral Bells) Heuchera sanguinea N, SW, SC, SE, HA
Astilbe Astilbe x arendsii N, SW, SC, SE
Balloon Flower Platycodon grandiflorus N, SW, SC, SE, HA
Bellflower Campanula spp. N, SW, SC, SE, HA
Blanket Flower Gaillardia . grandiflora N, SW, SC, SE, HA
Bleeding Heart Dicentra spp. N, SW, SC, SE, HA
Candytuft Iberis sempervirens N, SW, SC, SE
Chrysanthemum (short varieties) Deudranthuna x grandiflora N, SW, SC, SE, HA
Dianthus Dianthus spp. N, SW, SC, SE, HA
Coreopsis Coreopsis spp. N, SW, SC, SE, HA
Flax Linum perenne N, SW, SC, SE, HA
Forget-Me-Not Anchusa myosotis N, SW, SC, SE, HA
Hosta Hosta spp. N, SW, SC, SE, HA
Jacob’s Ladder Polemonium reptans N, SW, SC, SE, HA
Larkspur Delphinium spp. N, SW, SC, SE, HA
Lavender Lavandula angustifolia SW, SC
Lupine Lupinus spp. N, SW, SC, SE, HA
Mountain Bluet Centaurea montana N, SW, SC, SE
Penstemon Penstemon spp. N, SW, SC, SE, HA
Phlox Phlox spp. N, SW, SC, SE, HA
Pincushion Flower Scabiosa caucasica N, SW, SC, SE, HA
Rock Cress Arabis caucasica N, SW, SC, SE, HA
Silver Mound Artimisia schmidtiana N, SW, SC, SE, HA
Stoke’s Aster Stokesia laevis N, SW, SC
Stonecrop Sedum spp. N, SW, SC, SE, HA
Sundrops Oenothera fruticosa N, SW, SC, SE
Veronica Veronica spp. N, SW, SC, SE, HA
Shasta Daisy Leucanthemun x superbum N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston). HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


False Rock Cress

False Rock Cress is an outstanding rock garden specimen. Courtesy of FreeFoto.com

 

Groundcover Perennials

These plants develop greater spread than height and can be used in many landscape situations where low growth and coverage are needed, including rock gardens. Below is a list of groundcover perennials suitable for Idaho:

Common Name Scientific Name Regional Adaptation
Beach Wormwood Artimisia stelleriana N, SW, SC, SE, HA
Bishop’s Goutweed Aegopodium podograria N, SW, SC, SE, HA
Bugleweed Ajuga reptans N, SW, SC, SE, HA
Cranesbill Geranium spp. N, SW, SC, SE, HA
Deadnettel Lamium maculatum N, SW, SC, SE, HA
Hosta Hosta spp. N, SW, SC, SE, HA
False Rock Cress Aubrieta deltoidea N, SW, SC
Lamb’s Ear Stachys byzantina N, SW, SC, SE
Leadwort (Plumbago) Cerastostigma plumbaginoides N, SW, SC
Periwinkle Vinca minor N, SW, SC, SE, HA
Potentilla Potentilla verna N, SW, SC, SE, HA
Pussytoes Antennaria dioica N, SW, SC, SE, HA
Red Barrenwort Epimedium x rubrum N, SW, SC
Rock Cress Arabis caucasica N, SW, SC, SE, HA
Sea Pink (Sand Wort) Armeria maritime N, SW, SC, SE, HA
Snow-in-Summer Cerastium tomentosum N, SW, SC, SE, HA
Sweet Woodruff Asperula odorata N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.

Drought Tolerant Perennials

Some perennials can withstand hot temperatures and limited water availability and still be attractive. Below is a partial list of such plants.

Common Name Scientific Name Regional Adaptation
Aster (native species) Aster spp. N, SW, SC, SE, HA
Beach Wormwood Artimisia stelleriana N, SW, SC, SE, HA
Blanket Flower Gaillardia . grandiflora N, SW, SC, SE, HA
Butterfly Weed Asclepias tuberose N, SW, SC, SE, HA
Candytuft Iberis sempervirens N, SW, SC, SE
Coreopsis Coreopsis spp. N, SW, SC, SE
Globe Thistle Echinops ritro N, SW, SC, SE, HA
Lupine Lupinus spp. N, SW, SC, SE, HA
Mullein Verbascum spp. N, SW, SC, SE, HA
Orange Coneflower Rudbeckia fulgida var. sullivantii N, SW, SC, SE
Penstemon Penstemon spp. N, SW, SC, SE, HA
Purple Coneflower Echinacea purpurea N, SW, SC, SE, HA
Pussytoes Antennaria dioica N, SW, SC, SE, HA
Red Hot Poker Kniphofia uvaria SW, SC
Red Valerian Centranthus rubber SW, SC
Rock Cress Arabis caucasica N, SW, SC, SE, HA
Russian Sage Perovskia atriplicifolia SW, SC
Sage Salvia officinalis N, SW, SC, SE, HA
Sea Pink (Sand Wort) Armeria maritime N, SW, SC, SE, HA
Silver Mound Artimisia schmidtiana N, SW, SC, SE, HA
Stonecrop Sedum spp. N, SW, SC, SE, HA
Sundrops Oenothera fruticosa SW, SC, SE
Veronica Veronica spp. N, SW, SC, SE
Yarrow Achillea spp. N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston). HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Bellflower

Bellflower prefers moist soils

 

Perennials for Moist Conditions

Although consistently wet or moist soils are not common, especially in southern Idaho, such sites are often created artificially in the landscape. Below is a list of plants that thrive under such conditions.

Common Name Scientific Name Regional Adaptation
Astilbe (P) Astilbe spp. N, SW, SC, SE
Bee Balm Monarda didyma N, SW, SC, SE
Bellflower Campanula glomerata N, SW, SC, SE, HA
Cardinal Flower Lobelia cardinalis N, SW, SC, SE, HA
Delphinium Delphinium elatum N, SW, SC, SE, HA
Globeflower (F) Trollius europaeus N, SW, SC
Hosta (F) Hosta spp. N, SW, SC, SE, HA
Gooseneck Loosestrife Lysimachia clethroides N, SW, SC, SE
Ligularia (Leopard Plant) Ligularia spp. N, SW, SC, SE
Queen-of-the-Prairie Fillipendula rubra N, SW, SC, SE, HA
Rock Soapwort Saponaria ocymoides N, SW, SC, SE, HA

Columbine

Columbine is among shade tolerant perennials

 

Shade Tolerant Perennials

Perennials can be the backbone of shade gardens. Many of these plants are native to sites where partial or full shade is prevalent. They can be valuable for situations where other plants are marginally adapted. Below is a list of perennials that thrive in partial or full shade.

Common Name Scientific Name Regional Adaptation
Alumroot (Coral Bells) (P) Heuchera sanguinea N, SW, SC, SE, HA
Astilbe (P) Astilbe spp. N, SW, SC, SE
Autumn Fern (F) Dryopteris erythrosora N, SW, SC, SE, HA
Bergenia (P) Bergenia cordifolia N, SW, SC, SE, HA
Bishop’s Goutweed (F) Aegopodium podograria N, SW, SC, SE, HA
Bleeding Heart (P) Dicentra spp. N, SW, SC, SE, HA
Bugleweed (F) Ajuga reptans N, SW, SC, SE, HA
Cardinal Flower (P) Lobelia cardinalis N, SW, SC, SE, HA
Columbine (P) Aquilegia x hybrida N, SW, SC, SE, HA
Deadnettle (F) Lamium maculatum N, SW, SC, SE, HA
Foxglove (P) Digitalis purpurea N, SW, SC, SE
Globeflower (F) Trollius europaeus N, SW, SC
Heuchera (P) Heuchera sanguinea N, SW, SC, SE, HA
Hosta (F) Hosta spp. N, SW, SC, SE, HA
Japanese Painted Fern (F) Athyrium nipponicum N, SW, SC, SE, HA
Japanese Spurge (F) Pachysandra terminalis N, SW, SC, SE, HA
Liriope (F) Liriope spp. SW
Meadowrue (F) Thalictrum spp. N, SW, SC, SE, HA
Ostrich Fern (F) Pteris modulosa N, SW, SC, SE, HA
Periwinkle (F) Vinca minor N, SW, SC, SE, HA
Red Barrenwort (P) Epimedium x rubrum N, SW, SC
Sandwort (F) Arenaria spp. N, SW, SC
Yarrow, Fernleaf (F) Achillea spp. N, SW, SC, SE, HA

(P) = can withstand partial shade conditions
(F) = can withstand full shade conditions

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.

Most perennials do not bloom throughout an entire growing season. Knowing the period of bloom will help with determination of plant combinations that provide color all summer long. Below are lists of perennials classified by their flowering time. The dates are approximate and will depend on geographical location. The warmer valleys of Idaho may provide blooming conditions for many plants as much as 6 weeks earlier than the cooler northern or mountainous regions.


Gaillardia

Blanket Flower blooms all summer

Perennials with Extended Blooming Times

These are the exceptional plants that bloom over several months through spring, summer, and fall.

Common Name Scientific Name Regional Adaptation
Anthemis (Dyer’s Chamomile) Anthemis tinctoria N, SW, SC, SE, HA
Aster Aster spp. N, SW, SC, SE, HA
Balloon Flower Platycodon grandiflorus N, SW, SC, SE, HA
Bee Balm Monarda didyma N, SW, SC, SE, HA
Bellflower Campanula spp. N, SW, SC, SE, HA
Blanket Flower Gaillardia . grandiflora N, SW, SC, SE, HA
Butterfly Weed Asclepias tuberose N, SW, SC, SE, HA
Cranesbill Geranium spp. N, SW, SC, SE, HA
Deadnettle Lamium maculatum N, SW, SC, SE, HA
Dianthus Dianthus spp. N, SW, SC, SE, HA
Flax Linum perenne, Linum grandiflorum N, SW, SC, SE, HA
Hollyhock Alcea rosea N, SW, SC, SE, HA
Lavender Lavendula angustifolia SW, SC
Pincushion Flower Scabiosa caucasica N, SW, SC, SE, HA
Potentilla Potentilla verna N, SW, SC, SE, HA
Russian Sage Perovskia atriplicifolia SW, SC
Shasta Daisy Leucanthemum x supermum N, SW, SC, SE, HA
Veronica Veronica spp. N, SW, SC, SE
Yarrow Achillea spp. N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Poppies

Poppies provide spring color. Courtesy of FreeFoto.com

 

Early-Blooming Perennials

These are plants that bloom in early spring, typically March (warm areas), April, and May.

Common Name Scientific Name Regional Adaptation
Bleeding Heart Dicentra spp. N, SW, SC, SE, HA
Bloodroot Sanguinaria canadensis N, SW, SC, SE, HA
Blue False Indigo Baptisia australis N, SW, SC, SE, HA
Bugleweed Ajuga reptans N, SW, SC, SE, HA
Candytuft Iberis sempervirens N, SW, SC, SE
Columbine Aquilegia spp. N, SW, SC, SE, HA
Delphinium Delphinium x elatum N, SW, SC, SE, HA
Dianthus Dianthus plumarius N, SW, SC, SE, HA
False Rock Cress Abrietia deltoidea N, SW, SC
Forget-Me-Not Anchusa myosotis N, SW, SC, SE, HA
Gas Plant Dictamnus albus N, SW, SC, SE, HA
Jacob’s Ladder Polemonium reptans N, SW, SC, SE, HA
Mountain Bluet Centaurea montana N, SW, SC, SE
Oriental Poppy Papaver orientalis N, SW, SC, SE, HA
Peony Paeonia spp. N, SW, SC, SE, HA
Phlox, Creeping Phlox subulata N, SW, SC, SE, HA
Prairie Smoke Geum triflorum N, SW, SC, SE, HA
Pussytoes Antennaria dioica N, SW, SC, SE, HA
Rock Cress Arabis caucasica N, SW, SC, SE, HA
Sea Pink (Sand Wort) Armeria maritime N, SW, SC, SE, HA
Snow-in-Summer Cerastium tomentosum N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston). HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Asters

One of many summer blooming asters

 

Mid-Season Perennials

These are plants that bloom during the mid-summer months, typically June, July, and into August.

Common Name Scientific Name Regional Adaptation
Alumroot (Coral Bells) Heuchera sanguinea N, SW, SC, SE, HA
Aster Aster spp. N, SW, SC, SE, HA
Astilbe Astilbe x arendsii N, SW, SC, SE
Bee Balm Monarda didyma N, SW, SC, SE
Bellflower Campanula spp. N, SW, SC, SE, HA
Blanket Flower Gaillardia . grandiflora N, SW, SC, SE, HA
Butterfly Weed Asclepias tuberose N, SW, SC, SE, HA
Cardinal Flower Lobelia cardinalis N, SW, SC, SE, HA
Chrysanthemum Deudranthuna x grandiflora N, SW, SC, SE, HA
Deadnettle Lamium maculatum N, SW, SC, SE, HA
Coreopsis Coreopsis spp. N, SW, SC, SE
Flax Linum perenne N, SW, SC, SE, HA
Foxglove Digitalis purpurea N, SW, SC, SE
Gloriosa Daisy Rudbeckia x hybrida N, SW, SC, SE, HA
Goatsbeard Aruncus dioicus N, SW, SC, SE
Hollyhock Alcea rosea N, SW, SC, SE, HA
Larkspur Delphinium spp. N, SW, SC, SE, HA
Lavender Lavandula angustifolia SW, SC
Lupine Lupinus spp. N, SW, SC, SE, HA
Penstemon Penstemon spp. N, SW, SC, SE, HA
Phlox Phlox spp. N, SW, SC, SE, HA
Pincushion Flower Scabiosa caucasica N, SW, SC, SE, HA
Red Valerian Centranthus rubber SW, SC
Russian Sage Perovskia atriplicifolia SW, SC
Sage Salvia officinalis N, SW, SC, SE, HA
Shasta Daisy Leucanthemun x superbum N, SW, SC, SE, HA
Silver Mound Artimisia schmidtiana N, SW, SC, SE, HA
Stoke’s Aster Stokesia laevis N, SW, SC, SE, HA
Sundrops (Evening Primrose) Oenothera fruticosa SW, SC, SE
Veronica Veronica spp. N, SW, SC, SE
Yarrow Achillea spp. N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Sundrops

Fall blooming sundrops or evening primrose

 

Late-Blooming Perennials

These are plants that bloom in late summer, continuing into fall, many blooming through the earliest frost events. The time period for bloom will typically be August, September, and in warm regions continuing into October.

Common Name Scientific Name Regional Adaptation
Aster Aster spp. N, SW, SC, SE, HA
Chrysanthemum Deudranthuna x grandiflora N, SW, SC, SE, HA
Coreopsis Coreopsis spp. N, SW, SC, SE, HA
Deadnettle Lamium maculatum N, SW, SC, SE, HA
Globe Thistle Echinops ritro N, SW, SC, SE, HA
Gloriosa Daisy Rudbeckia x hybrida N, SW, SC, SE, HA
Leadwort (Plumbago) Cerastostigma plumbagonoides N, SW, SC, SE, HA
Lavender Lavandula angustifolia SW, SC
Mullein Verbascum spp. SW, SC, SE
Obedient Plant Physostegia virginiana N, SW, SC, SE, HA
Orange Coneflower Rudbeckia fulgida var. sullivantii N, SW, SC, SE
Phlox, Tall Phlox spp. N, SW, SC, SE, HA
Pincushion Flower Scabiosa caucasica N, SW, SC, SE, HA
Purple Coneflower Echinacea purpurea N, SW, SC, SE, HA
Red Hot Poker Kniphofia uvaria SW, SC
Russian Sage Perovskia atriplicifolia SW, SC
Sneezeweed (Helen’s Flower) Helenium autumnale N, SW, SC, SE, HA
Stonecrop Sedum spp. N, SW, SC, SE, HA
Sundrops (Evening Primrose) Oenothera fruticosa SW, SC, SE

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston). HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.

Planting certain perennial flowers can increase visits to the yard by butterflies and hummingbirds. Both flower color and flower shape create the attraction. Here are a few species that are effective at attracting wildlife.

The attraction of Butterfly Weed

The attraction of Butterfly Weed

Butterflies:
Common Name Scientific Name Regional Adaptation
Aster Aster spp. N, SW, SC, SE, HA
Butterfly Weed Asclepias tuberosa N, SW, SC, SE, HA
Goldenrod Solidago spp. N, SW, SC, SE, HA
Obedient Plant Physostegia verginiana N, SW, SC, SE, HA
Purple Coneflower Echinacea purpurea N, SW, SC, SE, HA
Yarrow Achillea millefolium N, SW, SC, SE, HA
Hummingbirds:
Common Name Scientific Name Regional Adaptation
Bee Balm Monarda didyma N, SW, SC, SE
Bleeding Heart Dicentra spp. N, SW, SC, SE, HA
Bugleweed Ajuga spp. N, SW, SC, SE, HA
Butterfly Weed Asclepias tuberose N, SW, SC, SE, HA
Bellflower Campanula spp. N, SW, SC, SE, HA
Cardinal Flower Lobelia cardinalis N, SW, SC, SE, HA
Columbine Aquilegia spp. N, SW, SC, SE, HA
Delphinium Delphinium elatum N, SW, SC, SE
Foxglove Digitalis spp. N, SW, SC, SE, HA
Lupine Lupinus spp. N, SW, SC, SE, HA
Red Hot Poker Kniphofia uvaria SW, SC

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello.
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston). HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.

Perennial weeds must be controlled before planting

Perennial weeds must be controlled before planting

Proper site selection is critical for success with perennials. Because the plants will reside in the same place for many years, they must be adapted to conditions where planted. If not, they may never reach their full potential for beauty in the landscape.

Major soil preparation in a perennial bed is completed only one time, just prior to planting. Consequently, to avoid future difficulties it must be done properly to ensure a healthy environment. First, kill and remove any persistent weeds and grass. Such weeds are difficult to manage once the beds are planted. This may take several months and multiple applications of a systemic herbicide. Next, make sure the site has good quality topsoil. This may require addition of topsoil, particularly in new home sites. Amend the soil by adding 2-3 inches of well-aged compost or manure. This is especially important in the arid, calcareous soils of southern Idaho. Add a complete fertilizer such as 5-10-5 at the equivalent of 3 lb/1000 sq. ft. of nitrogen. The fertilizer choice should be high in phosphorus and should preferably include sulfur in southern Idaho.

After amendments are added, the soil should be tilled to a depth of at least 8 inches, leveled, and smoothed (but not packed). Just prior to, or immediately after, planting it is a good idea to add two or three inches of mulch (wood chips, bark, etc.) to the soil surface. It may also pay dividends to place some type of edging or border material around the bed to slow encroachment of grasses or other weeds.

Four options exist for starting perennial plants. They are:

  1. direct seeding,
  2. indoor production of transplants from seed,
  3. purchasing and transplanting, and
  4. obtaining starts from existing plants.
Direct Seeding

Though the majority of perennials are vegetatively propagated to preserve trueness-to-type, some perennial plants may be grown from seed. Planting seed is the simplest and cheapest propagation method. The advantages of direct seeding are offset by the tendency for plants to be slow and erratic with respect to emergence and early growth. These are usually a problem only in the first year, during which they may delay flowering and shorten the color display of the bloom period.

Plant seed in shallow trenches and cover lightly. Plant extra seed and thin after emergence, if necessary. Refer to the seed package to determine seeding rate. Maintain good moisture at the soil surface by misting lightly until the plants emerge. Once plants are established, deeper irrigation should be applied only after the top 1-2 in. of the soil surface dries out.

Transplanting perennial seedlings into a well-prepared bed

Transplanting perennial seedlings into a well-prepared bed

Indoor Seeding and Transplanting

Growing your own transplants has the best features of both direct seeding and purchase of transplants. However, it has the same limitations of availability as direct seeding. The key to success is providing appropriate conditions for germination and early growth of the new seedlings. Soil, temperature, light, and moisture are the most important elements. The soil medium must be free of disease organisms that may cause death of germinating plants. The best soil medium is a commercial potting soil. Containers may range from recycled plastic pots, paper cups, or commercial seed plug trays. Wash and disinfect all containers before using. Temperatures should be warm enough to allow germination (e.g. 60-75 F during the day and slightly cooler at night).

Unless a greenhouse is available, artificial lighting will be required. Even a south facing window does not supply young plants with enough light to keep them from getting ‘leggy’ and weak. Some seedlings may need as much as 18 hours of light each day to remain healthy. Fancy equipment and expensive “grow lights” are not necessary. A standard fluorescent shop light, easily found at home improvement and hardware stores, fitted with one “warm,” and one “cool” tube works very well. Suspend the light fixture 12-18 inches from the plants and raise as growth occurs. It is also important to keep water availability balanced between too wet and too dry. This requires frequent, light irrigations.

Before transplanting, seedlings should be hardened off. This refers to the procedure of adapting the plants to outdoor conditions to reduce transplant shock. This can be done by placing the plants outdoors in full sun for increasing amounts of time each day for the last week or ten days before planting. Hardening the plants will improve survival and increase the early growth rate. The process of transplanting self-produced plants is identical to that described below for purchased plants.

Purchasing Plants

Buying established plants is the most common method of obtaining perennial plants. It is also the most expensive, but transplants will result in quicker establishment and a longer flowering period during the first year.

When choosing transplants, it is best to buy from a nursery or garden store with personnel knowledgeable about local growing conditions. This will assure availability of adapted species and varieties. Do not look for the largest plants, or necessarily, those that are in bloom. You want the perennial to spend it’s bloom period in your garden, not in the nursery! Seek plants with good dark green color, healthy root systems, and no sign of disease or pest problems. Try to find plants that have been hardened off, in order to aid the transition to the yard.

For most perennial plants, timing of transplanting should correspond with a date one week later than the last frost in your region. Even though some perennial seedlings will withstand relatively hard frosts, there is little advantage to early planting given the longevity of these plants. To estimate the last frost date in your area, look at the Idaho chart compiled by Ed Hume Seeds.

It is best to transplant on a cool, cloudy day with little wind. This will allow acclimation under conditions of limited water loss. After removing a plant from its container, tease roots away from the surface of the root ball. Don’t plant the seedlings too deep. Bury the root ball in a hole sufficiently deep only to bring the soil slightly above the pot soil level. Space the plants according to the instruction on the seed packet or nursery pot label. For the first 7-10 days, water the plants frequently and lightly. For the first few days, the root ball holds all of the roots and is the only source of water. The root ball will need to be wetted as often as it would in the pot until the roots can become established in the surrounding soil.

Frequent, light watering is needed after transplanting. Courtesy of FreeFoto.com

Frequent, light watering is needed after transplanting. Courtesy of FreeFoto.com

Obtaining Starts

Depending on the species, vegetative propagation of perennials is probably the most common method commercial growers use for starting new plants. Homeowners can take advantage of propagation techniques to obtain starts of flowers already in place in their own yard and other places. This requires permission from the owner and a little extra work, but may require no purchase.

A few precautions are needed before trying to propagate a perennial plant. First, it is important to inspect the source plant to make sure it is healthy and free of visible disease. Then it is important to obtain adequate knowledge of the best methods and procedures for propagation of the species of interest, including the proper time of year. Here is a description of the most commonly used propagation methods:

Division – Many perennial plants develop a large multiple crown as they age. These can be cut into two or more pieces to create new plants. This can be done by digging up the plant, dividing into pieces, then replanting each one, or by using a sharp spade to cut a portion from a plant left in place, then replanting the removed segment. This latter method minimizes disturbance of the original plant. Perennials commonly divided include Shasta daisies, phlox, daylilies, iris and chrysanthemums.

Stem Cuttings – Some perennials easily grow roots on stems cut from growing plants, allowing the production of new plants. This method is commonly used by nurseries in lieu of planting seed. Stem cutting is usually done indoors and involves removing a stem tip or middle piece of a healthy, green shoot and poking it into sterile, moist growing medium. The new cutting should be kept out of direct sun and covered with clear plastic (plastic cups work well if only a few cuttings are being rooted) to prevent moisture loss. It usually takes 2-3 weeks for cuttings to develop new roots and several more weeks to be ready to transplant. Many soft-stemmed perennials can be successfully stem cut.

Root Cuttings – Perennials with thick, fleshy roots can be propagated by removing a portion of root and replanting in a new location. It is done by simply digging up a portion of root, cutting it into segments, and replanting each piece. Usually, the larger the root cutting the faster a new plant grows and blooms. Root cuttings, as a rule, should be taken when plants are dormant. Perennials that usually respond well to root cutting include peony, baby’s breath, and bleeding heart.

Layering – Some perennials that vine or have long, flexible stems can be layered, This involves bending a stem to lay along the ground, then covering a middle portion with moist soil (use a pot if the plant will be moved a long distance), leaving the tip uncovered. The covered part of the stem will grow roots, after which the stem can be severed from the original, thus creating a new plant. The rooting process may be helped by scratching or gouging the stem on or below the portion that will be covered. Perennial vines can usually be successfully layered.

In his web site, Dr. Leonard Perry, University of Vermont, provides information on the best method for propagating individual perennial species.

Once established, most perennial plants are relatively carefree. In general, they require less in the way of fertilizer and water inputs than do annuals. However, as is true of all plants, some tender loving care is needed to keep them healthy and attractive.

wood chips for mulching

Wood chips as a mulch layer

Mulching

If not done before planting, it is beneficial to mulch the flower bed before heat of summer sets in. This will keep the soil cool, retain moisture, and help with weed control.

Irrigation

Perennial plants should be irrigated less often and to a greater depth than nearby lawn areas. Many perennial plants have effective rooting depths of up to three feet. During July and August, a weekly irrigation with about 2 in. of water should be adequate in most soils. In sandy soils, less water should be applied on a more frequent basis. The amount of water applied should be cut back during the cooler spring months, the late fall, and during those infrequent periods of rain. A few perennials are adapted to very moist or even saturated soil conditions. These must be watered more often.

Fertilization

Most perennial plants need very little in the way of fertilizer. They may benefit from a spring application of a fertilizer high in nitrogen at the equivalent of 1-3 lbs nitrogen per 1,000 sq. ft. On the other hand, some years, no fertilizer of any kind may be needed. Determination of requirement is based on growth response of the plants. If the previous year, plants were slow growing, small, or yellow in color, add fertilizer at the higher end of the recommendation. If they were growing well and looking nice, add at the low end of the recommendation. If they were vigorous, floppy, and too large, do not add any fertilizer.

seed head

Removing old seed heads will aid flowering

Manicuring

Although relatively carefree, some perennials need attention to remain attractive throughout the summer. Plants that look thin and leggy can be forced to produce more lateral growth by shearing or pinching off the growing point of each stem. Plants that have many stems may produce bigger stems and larger flowers if some of the stems are pruned out. Removing lateral flower buds, leaving only the top-most bud, will also make flowers larger. Plants that fall down or become floppy may need to be staked or interplanted with stiffer, more upright types of plants. Deadheading will prolong flowering of many perennials and make the plants more attractive.

Weed Control

There are no options to completely replace hand weeding in annuals. Mulching with organic matter or weed barriers will help by blocking germination and growth of weed seed. Perennial weeds that creep into beds create the most difficult problems. If hand cultivation provides inadequate control, it may be necessary to hand apply a herbicide, such as a glyphosate product, by hand with a sponge or other wicking material.

Perennials may require winter protection

Perennials may require winter protection

Winter Protection

In the fall, perennials (except those that provide some winter interest or seedheads for sustaining birds and other wildlife) should be cut back to a height of 3-4 inches. This will create a more attractive winter landscape and allow the crowns to be covered with a layer of mulch. Proper winter mulching consists of application of 3-4 inches of compost, leaves, wood chips, or other organic matter. The mulch should be removed from around the crowns in early spring to help prevent premature growth of shoots that may be damaged by frost and rot in wet spring climates.

Disease and Insect Control

It is beyond the scope of this site to provide specific pest management information for the large number of commercially available perennial species. Each has unique problems that may be more or less serious. However, there are many pests that are common and infest many types of plants. Diagnostic and simple control information will be given for these common pests in our sections on insects and disease problems. For detailed information on control of insects and diseases, as well as information of other pests, see the Insect and Disease Pests section of this site.

Aphids with a predatory lady bug larvae ©2004 Cornell Plant Pathology Herbarium

Aphids with a predatory lady bug larvae ©2004 Cornell Plant Pathology Herbarium

Insect Problems

Aphids: Also known as plant lice. Small, soft-bodied, sucking insects that cluster on the stems or underside of leaves. Aphids are usually wingless and green, brown, or black in color. Symptoms of infested plants include distorted or curled leaves, presence of sticky sap (honeydew) on the infested surfaces, and misshapen new growth.

Aphids can be controlled with the use of insecticidal soap or a registered insecticide. A strong stream of water directed at the infected plants may knock them from the plant. Many beneficial insects feed on aphids and if an infestation is not too severe, it may be appropriate to be patient and let nature take its course.

Caterpillars can be destructive

Caterpillars can be destructive

Caterpillars: Are the larvae of numerous species of moths and butterflies. These voracious legged worms come in many sizes and colors. Plant symptoms include chewed or completely missing leaves. Some types of caterpillars will roll or fold the leaves and hide inside. Often, frass or droppings are present on and around the plants.

A light infestation can be easily controlled by picking them from the plant a crushing them. Common registered insecticides will effectively kill caterpillars.

Leafminers: Are small insect larvae that burrow under the leaf surface while feeding. Symptoms are easily recognized and exhibit themselves as zig-zag or wandering lines on the upper leaf surface that are lighter in color that the rest of the leaf surface. These are tunnels in the leaves caused by leafminer feeding.

A light infestation of leafminers can be controlled by removing and destroying damaged leaves. A heavy infestation will require the use of a registered systemic type insecticide.

Mealybugs: Are sucking insects that infest stems of many plants. Mealybugs are easily recognized by the presence of a cotton-like white substance they deposit for protection.

Control of mealybugs can be had by spraying the plants with a direct stream of water, using and insecticidal soap, or using a registered insecticide.

Spider Mites: Not actually insects, these miniscule pests are actually related to spiders. They spin protective webs on the underside of leaves and feed by sucking juice from the leaves. Symptoms include color mottling that, at a distance, may appear as a general yellowing of older leaves. Webbing will be presence on the underside of infested leaves. The mites, to small to be easily visible, can be detected by shaking a leaf over piece of clean white paper.

Spider mites prefer dry, dusty environments. Sprinkler irrigation or routine washing of leaves with water usually keep them at bay. A severe infestation may require the use of a registered miticide. Most common insecticides are ineffective against spider mites.

Slugs and Snails: Prefer damp soil and humid conditions. Slugs and snails often hide during the day and feed at night. Symptoms include chewed leafs and glistening slime trails on plant surfaces.

Control snails and slugs with baits.

Thrips: Damage is cause by the larva of this small, four-winged insect. Thrips reside on the underside of leaves and use their rasping mouthparts to scrape away the surface of the leaf after which they feed on the sap. Symptoms appear as white streaks and blotches, more prominent on the underside of the leaf.

A light infestation does little permanent damage to the plant and can be ignored. A heavy infestation will likely require the use of a registered insecticide.

Whiteflies: In Idaho are more commonly a problem in greenhouses than they are outdoors. They are small insects with distinct bright white wings that reside and feed on the underside of leaves. Symptoms include the presence of honeydew on leaf surfaces, often accompanied by a lack sooty mold. When disturbed, clouds of the white, rapidly flying insects will rise above the foliage, then quickly resettle.

Trap the flies with yellow sticky boards or use a registered insecticide.

Disease Problems

Damping Off: Caused by fungal pathogens that infect seedlings at soil level, girdling the stems and causing death. Infected seedling will develop tan-colored, soft tissue at the base of the stem. The plants fall over and usually die. Once established and actively growing, plants seldom are affected by damping off.

Control measures include maintaining optimum soil moisture and planting into well-drained soils that are not overly wet. In extreme cases, a soil drench of a registered fungicide can be applied to the soil surface. However, by the time damage is observed it may be too late for control using fungicides.

Leaf Spots: Are caused by numerous fungal (occasionally bacterial) pathogens that penetrate and kill leaf tissue. Symptoms usually start and are worse on older leaves. These diseases are usually worse following periods of wet weather and high humidity.

Removal of all dead plant material at the end of the growing season helps prevent many leaf spot diseases the following year. In-season control usually requires use of a registered fungicide.

Powdery mildew on a perennial plant © 2004 Cornell Plant Pathology Herbarium

Powdery mildew on a perennial plant © 2004 Cornell Plant Pathology Herbarium

Powdery Mildew: Is caused by fungal pathogens. The classic symptom is a whitish, powdery growth present on leaf surfaces. Heavy infections cause distortions on new growth. Infections are often worse during summers that follow damp spring weather. Plants grown in shade are more prone to infection with powdery mildew

Prevention involved growing plants in a sunny location and making sure there is plenty of space and air movement around plants. Control usually requires the use of a registered fungicide.

Root and Stem Rots: Are caused by fungi (occasionally bacteria) that live in the soil. Infected plants initially develop mild wilting symptoms that become progressively worse and may eventually cause death.

Soil pathogens are difficult to control. They can best be prevented by planting resistant varieties, avoiding overly wet soil conditions, and destroying infected plants.

White Mold: Is caused by a fungus that overwinters in the soil. It infects plant stems that touch moist soil surfaces. Symptoms include a slimy, white mold that girdles and collapses the infected tissue. Leaves above the girdled stem wilt and die. In advanced stages, small gray structures that look like mouse droppings form inside a hollowed stem.

Prevention is the best strategy and involves staking stems off the ground, spacing plants to allow air movement around foliage, and irrigating infrequently to allow intermittent drying of the soil surface.

Virus: Not technically alive, viruses are small, disruptive pieces of genetic material that disrupt plant function. Symptoms vary widely and usually include some combination of stunting, yellowing, mottling, or leaf and stem distortion. Viruses are a particularly severe problem on perennials because their long life span and lack of seed propagation create many opportunities for chronic infection.

There are not control measures for viruses other than using resistant varieties or controlling the organisms (usually insects) that transfer them from one plant to another. Prevention involves removing and destroying any infected plants.

Information on control of garden insects and diseases common to Idaho can be found in the online Idaho Master Gardener Handbook.

Diagnosis information and specific control measures for diseases in the landscape is available from the University of Kentucky.

The University of Illinois Extension has published a bulletin on control of common insect pests in flower gardens.

University of Idaho Extension

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Room 52
606 S Rayburn St.
Moscow, ID

Mailing Address:
University of Idaho Extension
875 Perimeter Drive MS 2338
Moscow, ID 83844-2338

Phone: 208-885-5883

Fax: 208-885-6654

Email: extension@uidaho.edu

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Barbara Petty