Perennials & Biennials for Montana Gardens
Montana may have a short growing season, but once you know what varieties work best in our climate you can have beautiful flowers from year to year with a modicum of care. Here we will cover the basics: proper planting, watering, weeding, fertilizing and propagating, as well as provide a substantial list of herbaceous ornamentals that do well in most Montana climates.Last Updated: 01/19
by Dara Palmer
PERENNIAL PLANTS ARE THOSE THAT LIVE FROM
year to year. They die back to the ground in winter and grow up from the roots every spring. Biennials, on the other hand, form a rosette of leaves close to the ground in the first season; then produce stems, flower stalks and seed the second year, after which they die. Some new biennial cultivars have been developed that will bloom the first year.
Site Selection & Preparation
Aside from shade loving perennials and biennials, most plants require full sun for optimum performance. When selecting a site in the yard for a perennial bed or border, choose an area that gets at least six hours of sun a day in a spot with well-drained soil. Many plants don’t do well when their “feet” are wet, so take care not to plant in low, wet areas that don’t drain well or get much sun.
Because biennials, and perennials especially, are in the ground much longer than annuals, it is important to take some time creating a hospitable planting medium. First, get a soil test to determine the pH and nutrient content of the planting area. Many perennials won’t survive longer than one year if the soil is not properly prepared, therefore, it is good practice to amend the soil with organic matter at the rate of 2-4 cubic yards per 1000 square feet. Work the soil to a depth of 6-12 inches, adding any nutrients necessary as per the results of a soil test.
Aside from light and drainage requirements, consider color, spread, height, season of bloom and maintenance needs when choosing plants for the yard. Form (shape) and texture are also good elements to regard when selecting plants, especially considering that most perennials only bloom for 4-6 weeks, leaving just the foliage for interest. To ensure color and interest throughout the growing season, select plants with varying bloom times, heights, shapes and leaf textures.
Plants can be grown from seed and then transplanted, or sown directly in the garden. Be aware that seed saved from previous year’s plants may not be true to type. Purchasing container plants at a local nursery will offer the most variety. When selecting perennials and biennials from the nursery, choose from the center of the display, where plants are less likely to be dried out; pop the plant out of the pot and look at the roots, make sure they are firm and whitish in color; check the underside of the leaves for bugs and, although tempting, choose plants that are not already in bloom.
It is helpful to set out your potted plants in the bed to judge spacing and placement before planting. Unless the plan is to move or divide plants sooner than usual, remember to space them according to their mature size.
Dig a hole that is slightly wider than the pot and deep enough that the crown of the plant is at ground level. Gently remove the plant from the pot by pushing it out from the bottom or tipping it upside down in your hand; pulling it out of the pot from the top risks damage to the stems and leaves. If the plant is root bound in the pot and is not coming out, the pot can be cut away with scissors or a knife. In this instance, the roots will likely need to be teased apart to avoid girdling. To do this, simply use a knife and cut down the sides of the root ball in several places.
Set the plant in the prepared hole, spreading the roots out. Backfill with the amended soil while gently pressing around the root ball to remove any air pockets and establish good soil contact with the roots. Water thoroughly, adding soil if needed due to settling. Peonies will not bloom if they are planted too deep. They should be planted so that their “eyes” (dormant buds above the crown) are 2 inches or less below the soil surface (Figure 1, page 2).
FIGURE 1. Proper planting depth of peony
When watering, some consideration should be given to soil type; sandy soils will need to be watered more frequently than clay soils, due to their varying degrees of water holding capacity. However, a general rule of thumb is 1 inch of water per week, with deep, infrequent watering to encourage root growth. During hot, windy periods, more water may be necessary. Newly- installed plants may need more frequent watering until they become established. Overhead watering is not recommended as it can promote foliage disease and increase evaporation; a drip irrigation system or soaker hose is best.
Weed control is best done by hand to avoid damaging or disturbing the plant roots. Organic mulches such as shredded or chipped bark, pine needles or shredded leaves are useful in impeding weed growth; yet conversely, can also prevent the desirable spread of self-sowing biennials and perennials. The benefits of mulch outweigh the cons. A 4-6 inch deep layer of organic mulch around plants creates a uniform look while conserving soil moisture and providing soil nutrients and microorganisms. Mulch can be especially beneficial in the winter by insulating the plant from warm periods that may break dormancy, as well as protecting the plant crown from frost heaves.
Aside from the initial fertilizer application (done when preparing the planting site), additional nutrients may need to be added periodically, especially to plants that are heavy feeders (Astilbe, daylilies, peonies, delphinium and garden phlox, for example). Top-dressing with organic matter or broadcasting a general-purpose fertilizer in early spring may be sufficient for most herbaceous ornamentals. For plants needing more nutrients (and those in containers) a water-soluble fertilizer applied every few weeks will sustain healthy plants. A general schedule for side-dressing plants with fertilizer is to apply about 2 pounds of nitrogen per 100 square feet in early spring and again during the summer. Take care not to fertilize after July 1, which will stimulate vegetative growth that will not have time to mature prior to winter. Mulching plants with compost in the fall, after growth has slowed, will improve the soil as well as provide some nutrients.
Disbudding is the process of removing the auxiliary or lateral buds on each stem, to allow more energy to be sent to the main bud, which will then produce a single, large flower. Peonies respond well to disbudding. This process is often used in the floral industry and for blooms grown for exhibition.
Removing the spent flowers and immature seed pods from plants helps keep a garden bed looking clean and tidy, and helps maintain vigorous plant growth and often encourages a second bloom. Deadheading is very effective in controlling reseeding of plants that can become intrusive if left to self-sow (lady’s mantle, catmint). To deadhead, simply pinch or cut a declining flower and its stem back to the next lateral flower, leaf or bud. Cutting at an angle away from the main stem will help encourage water runoff, decreasing chance of disease.
Pinching and Shearing
Pinching and shearing are used to control the height of leggy plants and to encourage rebloom. Pinching is often done right after planting to focus plant energy to the root system and to promote a more compact growth habit. This also lowers the plants center of gravity which can help decrease the possibility of it flopping over later in the season. Similarly, shearing plants back to a height of 4-6 inches stimulates a more stout, well-branched growth. It is recommended to shear prior to bud formation to avoid removing potential blooms. Many perennials have the potential to flower a second time the same season. Shearing off the first blooms (and stems) as they are nearing expiration allows for a second flush of flowers, as well as a tidier appearance (sweet william, creeping phlox).
Tall ornamental plants or those with large, heavy blooms, will likely need staking to prevent damage to the stems and flowers, especially in windy conditions. Keeping plants upright and off surrounding vegetation also helps reduce the risk of disease and pests. There are many types of stakes available such as natural materials like bamboo and willow; plastic coated metal (which come in single stakes and hoops or rings); or also use stakes combined with string or twine to create a crisscross grid for stems to grow up through. To be sure the stakes don’t detract from the plant features, choose a stake that is about 6 inches shorter than the height of the mature plant. Stakes should be set when the plant is still small, about one-third of its mature size. When using stakes, be careful to not damage the roots of the plant, that plants are not tied too tight (if using twine) and that the stake and plant stem don't rub together, creating a wound.
Except for perennials that have desirable winter interest, most should be cut back in the fall after the foliage has died down. As a rule, remove the stems, leaves and spent flowers back to 2-4 inches above the ground to protect the crown from winter damage. Completely remove any dead or diseased specimens. Sedums and other plants with interesting features or seed heads can be left over winter and cut back the following spring before new growth begins.
Division is the easiest and most common way to propagate perennials. Aside from the desire to create starts for additional planting, dividing is often necessary to maintain the size, bloom production and health of the plant. Three to five years after planting, plants may show signs of decreased flowering or develop dead spots. This is the plant telling it is time to dig and divide the root ball. To do this simply dig up the entire plant. Use a spade or sharp knife to cut the clump into sections, allowing for 2-3 healthy buds per new clump (Figure 2).
Remove and discard any dead patches or areas with damaged roots or stems. Conventional wisdom dictates that spring blooming plants should be divided in the fall with all other plants being divided in the spring. There are a few exceptions to this rule; fleshy-rooted perennials like peonies, Oriental poppies and daylilies are best divided in the fall.
Spring division should be done when the plant has 2-4 inches of new growth, allowing a better look at healthy buds and to determine where division should occur. Division can still be done in the fall, but take care to do it early enough that the new plants have time to establish a root system before the ground freezes. Regardless of when to propagate, know that newly divided plants may not flower the first season.
FIGURE 2. Perennial division of Sedum (http:/www.mflandscapeanddesign.com)
|Scientific||Common||Type||Height||Spread||Bloom Season||Flower Color||
|Achillea spp.||Yarrow||Perennial||18-24”||18-28”||June-Sept||Yellow, white, red, orange||FS||D||'Moonshine’, ‘Paprika’, ‘Summer Pastels’|
|Achillea filipedulina||Fernleaf yarrow||Perennial||36”||24”||June - August||Yellow||FS||D||'Coronation Gold’|
|Aconitum spp.||Monkshood||Perennial||30-48”||12-18”||July - August||Purple||FS/PS||all parts poisonous|
|Aegopodium podagraria||Snow on the Mountain||Perennial||10-15”||12-18”||June||White||PS/SH||'Variegatum’, Can be invasive|
|Agastache spp.||Giant Hyssop||Perennial||24-36”||18-24”||July - Sept||Purple, blue||FS||D||Blue Fortune’, can reseed|
|Ajuga reptans||Bugleweed||Perennial||6-8”||ground cover||June||Purple, blue||FS/PS||‘Catlin’s Giant’, ‘Chocolate Chips’, 'Burgundy Glow’|
|Alcea spp.||Hollyhock||Biennial||6-8’||18-24”||Jun-Aug||White, yellow, pink, red, purple||FS||Susceptible to Hollyhock rust|
|Alchemilla mollis||Lady’s Mantle||Perennial||16-24”||15-18”||June-July||Chartreuse||FS/PS|
|Anemone||Anemone||Perennial||18”||18”||May & Sept||White, magenta, pink||FS/PS|
|Antennaria dioica||Pussytoes||Perennial||4-6”||10-12”||May-June||Pink, white||FS||D|
|Aquilegia spp.||Columbine||Perennial||1-2’||12”||May-Jun||Blue, red, white, yellow, et al.||FS/PS||Naturalizes|
|Aralia cordata||Japanese Spikenard||Perennial||3-5’||3-5’||July-Sept||White||PS||‘Sun King’, gold,/chartreuse leaves|
|Artemisia schmidtiana||Silver Mound Wormwood||Perennial||6-12”||ground cover||June-July||White||FS||D||poor||‘Silvermound’|
|Aruncus dioicus||Goatsbeard||Perennial||4-6’||2-4’||June-July||Cream, white||FS/PS|
|Asclepias tuberosa||Milkweed/ Butterfly weed||Perennial||1-3’||1-3’||July-Oct||Orange, yellow||FS||D|
|Aster||Aster||Perennial||12-18”||24”||Aug-Sept||White, pink, blue, purple||FS||‘Wood’s Purple’|
|Astilbe x arendsii||False Spirea||Perennial||12-24”||8-12”||June-Aug||Cream-White, red, pink||PS/SH||‘Bridal Veil’, ‘Fanal’|
|Astrantia major||Masterwort||Perennial||18-24”||18-24”||June-July||Pink, white, red||PS||'Moulon Rouge’, ‘Ruby Wedding’, ‘Magnum Blush’|
|Athyrium filix-femina||Lady Fern||Perennial||30”||12-24”||N/A||Green foliage||PS/FS|
|Aubrieta deltoidea||Rockcress||Perennial||8”||ground cover||Apr-May||Purple, blue, violet, red, white, pink||FS|
|Aurinia saxatilis||Basket of Gold||Perennial||8-12”||12-24”||Apr-June||Yellow||FS/PS|
|Baptisia australis||Blue wild indigo||Perennial||2-4’||18-30”||June||Blue||FS||D|
|Bergenia cordifolia||Heart-leaved bergenia, Pigsqueak||Perennial||12”||ground cover||Apr-May||Dark pink||SH|
|Brunnera macrophylla||Siberian Bugloss||Perennial||12-16”||15-18”||May-June||Blue||SH|
|Campanula medium||Canterbury Bells||Perennial||2-3’||12”||June-Aug||Blue, violet, red, white||FS/PS|
|Campanula rotundifolia||Blue bell, harebell||Perennial||12-18”||6-12”||June - Sept||Blue||FS/PS|
|Centranthus ruber||Jupiter’s beard, Red valerian||Perennial||18-36”||12-18”||May-June||Red, pale to crimson||FS/PS|
|Cerastium tomentosum||Snow in Summer||Perennial||3-6”||ground cover||May-June||White||FS||D|
|Clematis||Clematis||Perennial||7-10’||2-4’||June-Aug||Variety||FS/PS||Roots need to be shaded|
|Convallaria majalis||Lily of the Valley||Perennial||6-8”||3-6”||May-June||White, pink||PS/SH||Naturalizes, all parts poisonous|
|Coreopsis||Tickseed||Perennial||10-24”||12-18”||June-Aug||Yellow, orange, red||FS||D||'Moonbeam’|
|Delphinium||Larkspur||Perennial||4-6’||2-3’||June-Aug||Blue, white, pink, violet||FS|
|Dianthus barbatus||Sweet William||Biennial||6-12”||12”||May-Aug||Red, pink, white, bicolors||FS/PS|
|Dianthus plumarius||Cottage Pinks||Perennial||6-12”||12”||May-Aug||Pink||FS||D|
|Dicentra formosa||Fringed Bleeding Heart||Perennial||12-18”||12-18”||May||Deep Red, Cherry Red, Deep Pink||PS||'King of Hearts’, ‘Luxuriant’|
|Digitalis purpurea||Foxglove||Biennial||24-36”||18”||May-July||Pink, white, purple||FS/PS||Leaves poisonous|
|Doronicum macrophyllum||Leopard’s Bane||Perennial||18-24”||12-18”||Apr-June||Yellow||FS/PS|
|Echinacea angustifolia||Narrow-leaved Purple Coneflower||Perennial||12-24”||9-18”||June-July||Light pink, pale purple||FS||D||clay, dry, rocky||Compact, petals droop|
|Echinacea pallida||Pale Purple Coneflower||Perennial||24-36”||12-18”||June-August||Pale purple||FS||D||Self-seeds|
|Echinacea purpurea||Purple Coneflower||Perennial||24-36”||18-24”||Aug-Sept||Purplish-pink||FS/PS||D||poor||'White Swan’, ‘Magnus’; winter interest|
|Echinops ritro||Globe thistle||Perennial||36-40”||2-3’||July-Aug||Blue||FS||winter interest|
|Eutrochium purpureum||Joe Pye Weed||Perennial||5-7’||3-4’||July-Sept||Pink, magenta, mauve||FS/PS||W||winter interest|
|Gaillardia spp.||Blanket Flower||Perennial||18-24”||18-24”||July-Sept||Yellow, orange, red||FS||D||poor||'Arizona Sun’, ‘Burgundy’|
|Galium odoratum||Sweet Woodruff||Perennial||6-8”||ground cover||May-June||White||PS/SH||W|
|Geranium||Cranesbill||Perennial||8-20”||12-24”||May-Aug||Pink, magenta, blue, white||FS/PS|
|Geum||Avens, Prairie Smoke||Perennial||24”||12”||June-Sept||Red, orange, pink, white||FS|
|Heliopsis helianthodies||False Sunflower||Perennial||3-6’||2-4’||June-Aug||Yellow-orange||FS||D||clay||'Summer Sun’|
|Heuchera sanguinea||Coral Bells||Perennial||12-20”||12”||May-June||Red, pink||FS/SH|
|Hosta||Hosta, Plantain Lily||Perennial||12-24”||18-24”||Aug-Sept||White, lavender||PS/SH|
|Lamium maculatum||Spotted Dead Nettle||Perennial||8-12”||2-3’||May-July||White, pink, purple||PS/SH||'Pink Pewter’, ’White Nancy’, Purple Dragon’|
|Lamprocapnos spectabilis||Bleeding Heart||Perennial||24-36”||18-30”||April-May||White, pink||PS/SH||formerly known as Dicentra spectabilis|
|Lavendula angustifolia||Lavender||Perennial||12-18”||12-18”||June - August||Purple||FS||'Hidcote’, 'Munstead’|
|Leucanthemum x superbum||Shasta Daisy||Perennial||1-3’||2’||July-Sept||White with yellow center||FS||D|
|Liatris spicata||Gayfeather, Blazing Star||Perennial||24-36”||24”||July-Sept||Purple, white, Pink||FS||D||clay|
|Ligularia dentata||Rocket, Leopard plant||Perennial||3-4’||4’||June-July||Yellow||PS/SH||W|
|Limonium platyphyllum||Sea Lavender, perennial statice||Perennial||2-3’||2-3’||July-Aug||Lavender-blue||FS||D||May self-seed|
|Linum perenne||Perennial flax||Perennial||24”||12-18”||May-June||Sky blue||FS/PS||D||Will self-sow|
|Lobelia cardinalis||Cardinal flower||Perennial||2-4’||1-2’||July-Sept||Scarlet red, white, rose||FS/PS||W||Will self-sow|
|Lupinus||Lupine||Perennial||3-4’||12-18”||May-July||White, pink, yellow, blue, red, purple||FS|
|Lychnis chalcedonica||Maltese cross||Perennial||1-3’||18”||June-Sept||Red||FS|
|Lysimachia nummularia||Creeping jenny, Moneywort||Perennial||4-6”||24”||June||Yellow||FS/PS||W||Can become invasive|
|Matteuccia struthiopteris||Ostrich Fern||Perennial||2-3’||5-8’||N/A||PS/SH||W||clay||Rhizomatous|
|Monarda didyma||Bee Balm, Bergamot||Perennial||24-36”||2-3’||July-Aug||Red, pink, white, lavender||FS/PS||W||clay||Naturalizes|
|Monarda fistulosa||Wild Bergamot||Perennial||24-48”||24-36”||July - Sept||Pink/lavender||FS/PS|
|Nepeta x faassenii||Cat Mint||Perennial||1-2’||18-36”||June-Sept||Blue-violet||FS/PS||D||'Walker’s Low’|
|Pachysandra terminalis||Japanese pachysandra||Perennial||6-12”||ground cover||April-May||White||PS/SH||D||clay|
|Paeonia spp.||Peony||Perennial||2-3’||2-3’||May-June||Pink, red, coral, white, yellow||FS/PS|
|Papaver nudicale||Iceland poppy||Perennial||18”||12”||May-June||Orange, yellow, salmon, pink, white||FS/PS|
|Papaver orientale||Oriental Poppy||Perennial||24-48”||24-36”||May-July||Orange-red, white, pink, dark red, salmon||FS/PS||Naturalizes|
|Penstemon barbatus||Beardtongue||Perennial||18-36”||24-30”||May-July||Scarlet pink, red||FS||D|
|Perovskia atriplicifolia||Russian Sage||Perennial||3-5’||2-4’||July-Oct||Lavender blue||FS||D||clay|
|Phlox paniculata||Garden phlox||Perennial||2-4’||2-3’||July-Sept||White, pink, red, blue, purple||FS/PS||clay|
|Phlox subulata||Creeping Phlox, Moss Phlox||Perennial||3-6”||2’||Apr-June||Pink, white, red-purple, violet||FS||D|
|Polemonium caeruleum||Jacob’s Ladder||Perennial||18-24”||18-24”||May-July||Blue, pink, white||PS/SH|
|Pulmonaria spp.||Lungwort||Perennial||12”||12-18”||April-May||Rose pink, purple, blue, white||PS/SH|
|Pulsatilla vulgaris||Pasque Flower||Perennial||8-12”||8-12”||April-May||Pale or dark violet, red||FS/PS||Ornamental seed head|
|Ratibida columnifera||Prairie coneflower, Mexican Hat||Perennial||12-36”||12-18”||June-Sept||Yellow||FS|
|Rudbeckia hirta||Black-eyed Susan||Perennial||24-36”||12-24”||June-Sept||Yellow, Yellow-orange w/brown center||FS||D||clay||Short-lived|
|Rudbeckia fulgida||Black-eyed Susan||Perennial||24-36”||12-24”||June-Sept||Yellow w/brown center||FS||D||clay||'Goldstrum’; winter interest|
|Salvia nemerosa||Meadow Sage, Perennial salvia||Perennial||2-3’||24”||June-Sept||Violet purple||FS||D||'May Night’,|
|Saponaria ocymoides||Soapwort||Perennial||4-10”||ground cover||June-Sept||Dark pink||FS||poor|
|Scabiosa spp.||Pincushion flower||Perennial||18-24”||18”||July-Aug||Lavender, blue, white, pink, red, maroon||FS|
|Sedum spp.||Stonecrop||Perennial||3-24”||varies||Aug-Oct||Yellow, pink, red, white||FS||D||'Autumn Joy’, ‘Dragon’s Blood’, ‘Kamtschatium’, winter interest|
|Sempervivum tectorum||Hens & Chicks||Perennial||3-6”||6-18”||June-July||Reddish-purple||FS||D||poor|
|Stachys byzantina||Lamb’s Ear||Perennial||12-15”||12-18”||May-July||Purplish-pink||FS||D||Can become invasive|
|Tanacetum densum||Partridge feather||Perennial||6-8”||18-24”||June||Yellow||FS/PS||interesting silver foliage|
|Thymus pseudola-nuginosus||Woolly Thyme||Perennial||3-6”||ground cover||June-July||pale pink||FS||D|
|Thymus serpyllum||Creeping Thyme||Perennial||3-6”||ground cover||June-July||Deep pink||FS||D||Naturalizes, ‘Pink Chintz’|
|Trollius europaeus||Globeflower||Perennial||18-24”||24”||May-July||Yellow||PS/SH||W||May self-sow|
|Veronica spicata||Spike Speedwell||Perennial||12-18”||12-18”||June-Aug||Pink, red||FS|
|Veronica liwanensis||Turkish veronica||Perennial||3-6”||12-24”||April-May||blue||FS|
|Vinca minor||Common periwinkle, Creeping Myrtle||Perennial||4-6”||ground cover||May-June||Lavender blue||FS/PS||D||Naturalizes, winter interest|
|Yucca glauca||Soapweed||Perennial||2-5’||1-3’||June-July||Creamy white||FS||D||Self-seeds|
KEY: FS-Full Sun; PS-Part Sun; SH-Full Shade; D-Drought Tolerant: W-Tolerates wet soils