Montguide Banner

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, Montana Master Gardener Coordinator

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.

 

Plant Selection

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.

 

Planting

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

Proper planting depth of peony

 

 

Care

Watering

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.

Weeds

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.

Fertilizer

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.

 

Maintenance

Disbudding

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.

Deadheading

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).

Staking

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.

Fall Clean-up

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.

 

Propagation

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)

image

 

 

Scientific Common Type Height Spread Bloom Season Flower Color

Tolerances:

Light

Tolerances:

Moisture

Tolerances: 

Soils

Notes:

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
Armeria maritima Thrift Perennial 6-12” 8” May-July Pink FS      
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’
Hemerocallis spp. Daylily Perennial 15-40” 6-12” May-Aug Variety FS/PS      
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      
Iberis sempervirens Candytuft Perennial 6-12” 6-18” Apr-May White FS D    
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  
Solidago spp. Goldenrod Perennial 4-6’ 18” July-Oct Yellow FS/PS      
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


To download more free online MontGuides or order other publications, visit our online catalog at our store, contact your county or reservation MSU Extension office, or e-mail orderpubs@montana.edu.
Copyright © 2022 MSU Extension
We encourage the use of this document for nonprofit educational purposes. This document may be reprinted for nonprofit educational purposes if no endorsement of a commercial product, service or company is stated or implied, and if appropriate credit is given to the author and MSU Extension. To use these documents in electronic formats, permission must be sought from the Extension Communications Coordinator, 115 Culbertson Hall, Montana State University, Bozeman, MT 59717; E-mail: publications@montana.edu

The U.S. Department of Agriculture (USDA), Montana State University and Montana State University Extension prohibit discrimination in all of their programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital and family status. Issued in furtherance of cooperative extension work in agriculture and home economics, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Cody Stone, Director of Extension, Montana State University, Bozeman, MT 59717