Basics of a perennial garden

  • Article by: NANCY ROSE , Contributing Writer
  • Updated: April 26, 2000 - 11:00 PM

I want to plant perennials in a 4-by 9-foot raised flower box in front of my house. Can you suggest some flowers that would look nice together?

There are so many wonderful perennials available that it's hard to know where to start. Your selection should reflect your tastes, but there are some important basics to think about when planning a perennial bed.

The mature height and width of the plant, its bloom time and duration and its cultural requirements are as important to consider as the color of the flowers. You also should know the form (mounded, spiky, creeping, etc.) and texture (fine, medium, coarse) of the plants and strive to use a combination of these. Taller perennials should generally go toward the back if the bed will be viewed from one side, or toward the middle if it will be seen from all sides. Low mounded or creeping perennials should go toward the outer edges where they can be seen.

In order to have a succession of flowers throughout the season, select perennials that bloom at different times. Different cultivars within a group, such as daylilies or peonies, can have varying bloom times; check nursery catalogs or reference books to learn whether a cultivar blooms in early, mid-, or late season. By selecting several different cultivars you can have daylilies in bloom for nearly three months. It's also a good idea to select some perennials that have long individual bloom periods, because they will provide color for a long time. In my garden, 'Sunny Border Blue' veronica, 'Goldsturm' coneflower (Rudbeckia fulgida 'Goldsturm'), balloon flower (Platycodon grandiflorus) and purple coneflower (Echinacea purpurea) can be counted on to provide months of color.

Don't overlook the importance of foliage in a perennial garden. Including perennials that have attractive foliage greatly helps make the bed look full and healthy. Siberian iris (Iris sibirica), hosta, astilbe, peonies, lungwort (Pulmonaria) and silvery leaved artemisias, such as 'Lambrook Silver' and 'Valerie Finnis,' have great-looking foliage throughout the summer.

While there are hundreds of perennials to choose from, there's also something to be said for simplicity, especially in a fairly small garden bed such as yours. A single specimen of a large plant, such as a peony or gasplant (Dictamnus albus) is suitable, but many other perennials look better when planted in groups of three or more. That way, you can have blocks of color and avoid the hodge-podge effect of having one of dozens of different plants. And remember that that little perennial in a quart-sized container may grow into a 3-foot clump within just a few years.

Since you said you plan to grow these perennials in a raised box, I should mention winter protection. If your bed is barely raised above ground level, perhaps just the height of a railroad tie or landscape timber, then you would give it the same winter protection as a regular garden bed. However, if your planting box is raised several feet above ground level, then you may have to provide more winter protection. Beds or containers that are well above ground subject plants' roots to much colder temperatures than ground-level beds. You may have to stack bales of straw or bags of dry leaves all around the planter to protect the plants.

Before you start planting, look at some catalogs and books to get an idea of what perennials you like. Some good perennial books include "Rodale's Illustrated Encyclopedia of Perennials" (C. Colston Burrell and Ellen Phillips), "Perennial Combinations" (C. Colston Burrell) and "Growing Perennials in Cold Climates" (Mike Heger and John Whitman). It's also fun to visit gardens such as the Minnesota Landscape Arboretum in Chanhassen and Noerenberg Garden in Orono to see what perennials are used there.

I love roses but I don't want to have to tip and cover the plants every year, which is what you have to do with hybrid tea roses around here. Can you recommend any good hardier shrub roses?

Shrub roses have been gaining in popularity, and for good reasons. In addition to having beautiful flowers, many shrub roses are winter hardy, require less maintenance than hybrid tea roses and work better as landscape plants. Shrub roses encompass a range of species and cultivars, with an accompanying range of plant sizes, flower forms and colors, hardiness and disease resistance.

Rugosa roses (Rosa rugosa) and hybrid rugosas are good selections for cold-climate landscaping. Rugosa rose is very cold hardy (USDA zone 3) and most of the hybrid rugosa are hardy through zone 4 and possibly colder. These shrub roses tend to be quite disease resistant and bloom heavily in early summer, then more lightly the rest of the summer and early fall. On the down side, they tend to send out a lot of suckers and have an unkempt growth habit. My favorite rugosa rose cultivar is 'Frau Dagmar Hastrup' (sometimes spelled Hartopp), which has fragrant pale pink flowers, large red-orange hips and glossy dark green foliage. Other favorites include 'Blanc Double de Coubert,' 'Belle Poitevine,' 'Thrse Bugnet,' 'Robusta' and the newer Pavement Series from Europe.

A number of shrub roses from Canada have proven to be good choices for this area also. Two groups of these roses are the Explorer and Parkland series. These shrub roses have a number of different species in their parentage and the resulting cultivars range from low-growing, semi-miniatures such as 'Royal Edward' to the almost overly vigorous 'William Baffin,' whose 8-inch-long canes can be trained over supports like a climbing rose. Some of the other cultivars available include 'Winnipeg Parks,' 'Morden Centennial,' 'Alexander MacKenzie' and 'Louis Jolliet.'

Some other shrub roses worth mentioning are 'Chuckles,' 'Nearly Wild,' 'The Fairy' and 'Carefree Beauty.' The latter is one of the Buck roses from Iowa, a group of shrub roses that are gaining popularity in the Midwest. Most of the Buck roses will die to the ground over winter in northern zone 4, but will regrow and flower well each summer. 'Knockout' is a new repeat blooming shrub rose with cherry red flowers. It is listed as hardy to zone 4, though it hasn't been out long enough for a full winter trial here at the colder end of zone 4.

-- Nancy Rose is a research horticulturist at the Minnesota Landscape Arboretum. She spends her spare time gardening, inside or outside, depending on the weather. Please address gardening questions to her at the Minnesota Landscape Arboretum, P.O. Box 39, Chanhassen MN 55317. She will answer questions in this column only.

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