Perennials Archives

Sedum surrounds stepping stones at a private garden in Saint Louis

There are some places that lawn grasses just don’t do well in.  If you’ve planted (and replanted, and maybe replanted again) grass into an area with little success, you might consider a perennial ground cover.  There are perennials for dry sunny areas, including thyme and sedum; dry shady areas (barrenwort), and plenty for just average sun and soils–maybe mazus.

Some premium groundcovers like the barrenwort are available only in larger pots; and of course we have the standard pachysandra and liriope for large scale plantings in the shade.  If you want to play around a little, we offer  two lines of perennial ground covers–Stepables and Treadwells–they offer lots of possibilities to end the spotty lawn blues; especially for small scale plantings.

My view on perennial ground covers is that they are going to be best in limited traffic areas—between flagstones, in rock walls, in containers, but not where the kids are playing football every weekend.  Try them in a limited area to start, and see how you like them. You can always expand the area later on if you are happy with the results. Heck, they’re ground covers–you may be able to dig out divots and expand the area from your own initial planting after the first season.  Remember that especially in the first season, they will need to be weeded and watered so that they establish and spread.

Mazus at the Missouri Botanical Garden, Saint Louis

Also consider that if they are really happy, many ground covers can be very aggressive and spread into lawns and flower beds.  Another reason to try a dozen in a limited area to see how they perform over the season before ripping up the entire lawn.  Ajuga and lysimachia, for example are notorious for moving into lawns and also are on lists of invasive species.

Ajuga and sedum between stepping stones at a private garden in Saint Louis

I have seen some terrific  plantings of Stepables and Treadwells, and when done well, they definitely are more interesting than turfgrass.  They are especially nice when setting off a bench, birdbath, statuary or some other garden fixture for example.  Remember that even shade-tolerant ground covers need light to live and grow thickly.  You are never going to get a lush ground cover under a spruce or pine tree that casts a year round, dense shadow.

Remember, too, that the ground covers can be used in your mixed container plantings.  Mixed containers need elements: a “Thriller”—the focal point, often with a vertical aspect;  a “Filler”, something for the mid-level; and a “Spiller,” to cascade over the edge of the pot.  Successful container plantings often resemble exuberant raised fountains, with the thriller being the jet of water; the filler the area where the water splashes to the container; and the spiller being the water cascading down the sides.

Shady groundcovers: woodland creeping phlox and Epimedium at the author's home

Many of the ground covers, like the above mentioned lysimachia (moneywort), English Ivy (a container is the only place it should be planted), wirevine (Muhlenbeckia), or mazus being types that you might try as “spillers.”

In addition to the Treadwells and Stepables, we have other ground covers available periodically, including barrenwort (Epimedium) and hayscented fern for example; plants  that for one reason or another (either cost or production issues)  keep them from being included in the above programs.

Behnke’s also has the standard ground covers, the usual boring liriope, pachysandra and vinca. So boring, we relegate them to the woody plants department instead of perennials.  We have a mystique to protect, after all.

A Little Information on Dianthus

Dianthus Cranberry Ice

Dianthus Cranberry Ice

On special this week in our perennial department is the entire selection of Dianthus. Garden dianthus are commonly called pinks, because the edges of the petals are often notched as if cut with a pinking shears. We also have some called “Sweet William,” which is usually grown as a biennial (they tend to die after a season of flowering, but will usually seed themselves and thus return to your garden year after year). Dianthus is one of the mainstays of the “English Cottage Garden” look, which points you in the direction of their siting and care.


In our area, the pinks give their best bloom in spring—April, May, early June. Sometimes they cough up a few flowers in the summer and fall as well, especially in cooler years. As perennials go, they tend to be short-lived. You may find that they need to be replaced after several years.
They offer pink, red, white or bi-colored flowers, often very fragrant. Carnations, the cut flower, are a type of dianthus, so that might give you a sense of the fragrance. (Carnations are not good garden plants, but if you use your imagination, some of the double pinks look like wee carnations.)

Dianthus 'Feuerhexe' or Fire Witch

Many of the cultivars offer silver or blue evergreen foliage, which can be attractive when the plant is not in bloom. We found over the years that an older variety, ‘Bath’s Pink,’ can make a good silver ground cover for small areas. Our most popular dianthus is ‘Feuerhexe’ or “Fire Witch,” bearing electric pink flowers on blue foliage. It was the Perennial Plant Association’s Perennial of the Year a few years back. This time of the year we generally have a dozen or more cultivars in stock, with the early ones like Fire Witch and ‘Tiny Rubies’ just coming into bloom now.

Even when not in bloom, 'Bath's Pink' can be a nice groundcover, photographed at the Missouri Botanical Garden in July.

Plant them in containers, or on a slope, or in a raised bed… somewhere with good drainage. Sodden winter soil will kill them. Add a little lime to the soil when you plant, and site them in a sunny spot. As with many perennials, if you have a chance to pluck off the dead flowers, it will encourage the plant to send up additional blooms, extending the flowering season. My experience is that they go more or less heat dormant in the hottest part of summer, sending out new growth starting early to mid-September. The new growth will have more intense blue/silver foliage. Don’t prune, trim, cut back, etc during July and August. Do it in the early fall.

Dianthus don’t mind the cold! Snow on pots of Dianthus, April 7, 2007, Behnke’s Garden Center at Beltsville

As I age, I am becoming more and more fond of fragrant flowers. (This is a change over time. I used to be a hardcore horticulturist, interested in flowers that look and smell like rotten meat and are pollinated by flies and carrion beetles. I’m still interested, but no longer want them in the garden. Much to the relief of the neighbors.) If I didn’t happen to own a wooded lot without much sun, you can bet that I’d save some space for the pinks. Perhaps at that retirement cottage we plants people all dream about…

Tyne Cot Military Cemetery, Belgium

Hellebores – The Glory of the Garden

This was written several years ago, so certain references like “lack of snow cover” may sound a little odd. Overall, the information is still good. [Editor]

The warm weather of the previous weekend perked up both the garden and the gardener, as I ventured outdoors to do some projects. The foliage on many of the “evergreen” perennials burned this year, due to the cold weather in January and February combined with lack of snow cover. I trimmed the Epimedium to the ground, in anticipation of its April flowers, and cut the old leave off of the hellebores.

Some years the hellebore foliage looks pretty good right into late spring, but this year, there was some edge burn. Easily taken care of by just cutting those old leaves off at the ground while being careful not to cut the new leaves and flowers emerging from the center of the clump.

Read the rest of this entry

Gardening Basics: Perennials

WheelbarrowSimply Put: Perennials

In the previous post I talked about annuals. In quick summary: seed, germinate, grow, flower, flower, flower, I am so pretty, flower, flower, oh my biological clock is ticking, make seed, die. Time elapsed, one year or less.

Perennials are plants that grow for more than a year (assuming they live; it’s a life style, not a contract with God). They take their time; frequently they don’t even bloom in the first year of growth after the seed germinates.

When they do get around to blooming, perennials have shorter blooming seasons than annuals, or, if they bloom for several months, usually the first few weeks are intense and the re-bloom is more sporadic, sometimes requiring some encouragement on the part of the gardener. This might be something like shearing a couple of inches off of the top of the plant to remove the old dead flowers

Perennials tend to be either cool weather, late winter/spring bloomers or warm weather summer bloomers (but not both). There are even a few fall bloomers. The summer bloomers tend to have longer blooming periods than the spring bloomers.

We know a few things about garden center shoppers. We know that most of you a) shop in the spring, and b) you tend to buy what is in flower when you shop. Because a lot of the fun of perennial gardening is watching things change from day to day and week to week as plants grow and come into flower, you really should visit the garden center a couple of times in the summer to see what’s currently in bloom. Really. It’s for your own good.

Of perennials, it is said that the first year they sleep, the second year they creep, and the third year they leap. So, during the first year after you plant your perennial, not that much happens. The second year (after the first winter) you have more blooms on larger plants, and the third year, they really hit their stride with much larger plants and heavier bloom. Assuming everything goes right.

Most perennials die completely down to the ground in the winter, overwintering with living bits below ground. Or, they overwinter with small tufts of foliage (leaves) above the soil. Technically, these are “herbaceous perennials.” While we are jargoning, we may as well toss in hardy, which means they tolerate some below freezing temperatures. So what we are talking about are hardy herbaceous perennials: you’ll do fine if you just say “perennials.”

There is another outdoor herbaceous group that falls between the annuals and perennials, the biennials: plants that grow without flowering the first year, flower the second, and then die (so bi-ennial; two years). These include cabbage, parsley, and foxgloves. These are sold with the vegetables, herbs, or perennials, wherever they seem to fit the best. There aren’t that many.

Why use perennials? Most people do it to save the effort of replanting annuals each year. This does save some planting time, but for a perennial garden to look good, it does require some care—cutting back old flowers and so on—so planting perennials doesn’t save much time, it just spreads it out. The real reason to choose perennials is that it allows you, should you be inclined, to “paint” with flowers. Perennials change in many dimensions over the season—height, width, color; texture of foliage (fine or broad leaves); how one color plays off the colors of surrounding plants. So, you really get to play. If you enjoy repainting your walls with new colors, then you will enjoy painting the garden with perennials.

Planting tip: perennials are best planted in groups, three or five plants of a given type. If you have a big enough space, you can repeat the group in several spots to “unite” the garden.

How to Handle your Hosta

Behnkes Banks on ‘Shade Aristocrats’

The large, coarse leaves of most hostas tend to break up the monotony found in many landscape designs.

With various sizes, colors, light requirements, foliage shapes and textures, it is possible to fit an easy-to-grow hosta into almost any landscape situation.

When to Plant
Hostas can be planted in this area from March through November.

Where to Plant
Plant hostas where the proper shade conditions exist. Blues lose their color in sun, so they look their best with at least 50% shade. Golds tolerate sun quite well but should be shaded from the mid-day sun. Most hostas prefer dappled shade throughout the day. The soil should drain well and still be able to retain moisture.

hosta-Sieboldiana-ElegansHow to Plant
Dig bed for hostas 12 to 18 inches deep. Make a soil mixture of one third each existing soil, fine pine bark and organic matter such as peat moss, dehydrated manure or garden compost. Loosen root system using a garden cultivator and set plant in bed so top of root ball is even with or slightly higher than garden soil level. A handful of an organic fertilizer such as Plant-tone may be added to the backfill. Firm the plant in and water slowly and thoroughly until the water puddles around the plant. When water has soaked in , a mulch of shredded hardwood or pine bark 1 to 2 inches deep should be applied.

Long Term Care
Water is the most important requirement for hostas, especially the first year or two after planting. We suggest 3 to 5 gallons per week per plant if there is not sufficient rainfall. After the first 2 years, hostas have developed good root systems, and can withstand considerable drought. Hostas can thrive amazingly well with no further fertilizer, but an occasional side dressing of slow-release organic fertilizer in midsummer proves to be quite rewarding. In autumn, after foliage has died from frosts, the leaves should be trimmed off.

Trouble Shooting
The main problem with hostas is slugs and snails. These pests prefer moist, dark areas, feeding mostly on the soft, new, immature growth. Sanitation and a proper watering program are quite effective in controlling them.

Remove debris that provides hiding places and water only in the morning so plants are dry at sunset. Slug bait is also very effective in providing control. Manufacturers’ instructions and recommendations should always be followed with these products. Many of the new varieties of hostas are being bred for more pest resistance. Also, it’s nice to know that the older a plant gets, the more pest resistant it becomes.

Now that you know how to plant and maintain your hostas, sit back and watch them grow.

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