Perennial Flowers and Plants

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.

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.

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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
Lavendar	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.

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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.

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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

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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.

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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.

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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.

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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
Lavendar	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.

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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
Lavendar	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.

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.

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.

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.

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.

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.

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.

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.

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: 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: 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.