Selecting, Using, and Maintaining Perennials & Ground Covers

Perennials & ground covers are employed in a number of different ways - limited only by the imagination. Popular uses include the following:

As a Turf Substitute / Living Mulch.
The most important application of ground covers is to use them to eliminate or reduce the amount of turf grass in the landscape. Not only is this better for the environment, in the long run it saves time and money. It also helps give the landscape a unique character that can not be created with turf grass.

For Easing Transition and Creating Unity.
Using ground covers of intermediate height, color, or texture between and surrounding two contrasting elements (such as a beech tree with smooth gray bark and an oak with coarse dark brown bark) eases the perception of change and unites the features. Ground covers can be used in this manner to join the house with a surrounding woodlot, shrubs with trees, ornaments or benches with walkways, etc.

For Controlling Erosion.
Densely rooted ground covers are excellent for holding soil in place on slopes and areas of water runoff.

As Edging/Hedging.
Nonspreading types of ground cover can be used as edging or dwarf hedges to create geometric designs, direct traffic, and delimit borders and property lines.

As A Filler Between Steps, Paving, and Patio Stones.
Low growing "Foot Friendly" ground covers tolerate foot traffic and look fantastic in the cracks between steps and stones in the landscape. Here they add an element of color and softness. They also exclude weeds, prevent erosion, and in some cases release pleasant fragrances when stepped upon.

For Accent.
Used as accent plants, ground covers can be used to draw the eye to such features as statuary, benches, brickwork, entryways, steps, and other plants.

As Specimens.
The more unusual/showy ground covers can stand alone as specimens and should be sited in locations where the eye naturally falls such as atop a terrace, by a building entrance, outside of windows, and along the edge of steps.

As a Facing.
When sited in front of other plants, benches, statues, ornaments, and building foundations some of the taller ground covers do an excellent job of concealing the bases of these elements - a practice known as facing. Employed this way, they also help ease the transition between such elements and the space that surrounds them.

To Reduce Glare.
Ground covers absorb light and reduce glare, therefore when used along boulevards, roadways, parks, and parking lots they increase visibility and safety.

For Cooling Air and Controlling Snow Drifting.
Through transpiration (evaporative cooling) ground covers are natural air conditioners. During the winter (especially grassy types and those with woody stems) they trap snow and reduce blowing and drifting.

What are Perennials?

Perennials are typically herbaceous (non-woody) plants that live indefinitely. Some perennials are woody at the base with herbaceous branches. Many perennials, like Hostas and Dayliles, are deciduous and die back to the ground each winter as they go dormant. Others, such as Coral Bells and Bergenia are evergreen. Perennials come in a broad array of shapes, sizes, and colors and are known for their durability, beauty, and versatility as they perform many useful roles in the landscape.

Perennials are great for creating year-round interest through color, fragrance, and texture. Some purple leaved coral bells varieties are so dark purple as to appear black, and some of the bright yellow sedges, like 'Evergold', have color highlights that rival the sun. Other perennials, like the Asiatic lilies, bring exquisite fragrances, and others have mint or citrus scented leaves, such as calamint savory, lemon balm and lemon thyme. Textural extremes range from the thread-thin leaves of Coreopsis 'Moonbeam' to the 3-foot-wide foliage of giant butterbur.

Perennials can be used for ground covering (see Ground Covers, below) or to accent or highlight various features of the garden. They can do this by lining pathways and patios for a richly organic effect, with such plants as hostas, tall sedums, and iris. Likewise, perennials can be used to enhance and soften the look of boulders, walls, benches, poles and statues when planted in small groupings in front of or beside such features.

Perennials also provide habitat for songbirds, hummingbirds, butterflies and honeybees, and do this with their flowers, seed, and foliage. The flowers provide carbohydrate rich nectar and pollen for hummingbirds, butterflies and honeybees. Seed provides food for finches and other small birds. Even the foliage is important, and acts as a protective shelter, incubation site, and food source for the larval stages of butterflies.

What Are Ground Covers?
Ground covers are plants, which when properly cultured and established, require little maintenance and densely cover the soil in a manner that discourages and prevents the growth of weeds. For the most part, without pruning, ground covers range in height from less than an inch to about 4 feet tall. Ground covers may be succulent, herbaceous, or shrubby. They can be clumping, vining, or sprawling, and may be deciduous, evergreen, or semievergreen. Even some ferns and grasses can function as ground covers.

Ground covers are available in a broad array of colors and textures. In addition to green-leaved forms, there are red-, blue-, purple-, silver-, coppery-, bronze-, and gold-leaved selections. Multicolored (variegated) forms also exist, and textures range from fine to coarse, and soft to rough.

Material and Environmental Benefits of Ground Covers.
Reduced maintenance expense (in comparison to turf grass) is the primary financial advantage ground covers have to offer. Generally speaking, turf is less expensive at first, but considering its ongoing maintenance needs (frequent mowing, edging, fertilization, irrigation, disease and weed control, etc.), it proves to be more expensive in the long run.

Much annual cleanup work (and expense) can be eliminated by using ground covers. In nature, a cycle exists in which microorganisms reduce organic matter (i.e. leaves, fruit, twigs and and flowers) into humus. The humus, rich in nutrients, is the source of fertility that assures the continuation of life. Ironically, in our landscapes we often disrupt this cycle (with back breaking labor, usually on weekends!) by raking and vacuuming up fallen fruits, leaves, flowers, and twigs. Instead, if we were to underplant our trees and shrubs with carefully selected ground covers, such organic debris would not only be concealed, but would rot, be returned to the soil, and would furnish nutrients to the ground covers.

The environmental benefits of ground covers should not be overlooked either. Ground covers control erosion, reduce snow drifting during winter, and humidify, oxygenate, and cool the air.

Aesthetic Benefits of Ground Covers.
Ground covers unify unrelated elements in the landscape. For example, consider a brown brick house constructed on a streamside lot. The coarse-textured, symmetrical, brick house and the clear, silvery, winding, tranquil stream have little in common. Yet, by using ground covers creatively, such as a broad sweeping bed of purple wintercreeper, the two can be joined in harmony. Similarly, by softening the sharp edges and angles of benches, drives, fences, and walks, ground covers can make such features seem at home among the living elements- trees, shrubs, and other plants.

Ground covers are indispensable for creating a rich, enjoyable, inviting atmosphere. Using sweeping beds of loosely arranged ground covers (as edgings along walkways) communicates a pleasant, welcoming message to those who visit.

Additionally, ground covers function in altering perceptions. To convey the impression of spaciousness, use small leaved smooth textured ground covers in broad, curving plantings. On the other hand, use large leaved coarsely textured ground covers to create the perception of intimacy and closeness. Brightly colored or fine textured ground covers tend to lighten areas and elevate or intensify one's mood. Shades of blue, green, or gray, particularly if the leaves are large and smooth textured, tend to enhance feelings of tranquility and peacefulness.

For relieving monotony in the landscape, ground covers are paramount. Entryways, steps, decking, ornaments, and trees and shrubs are infinitely more interesting when accented with ground covers. Amazing for their intricate branch patterns, colorfully painted foliage, and sometimes attractively flaking bark, ground covers can enhance feelings of joy and light-heartedness. Evergreen ground covers exhibit year-round beauty, while many others grace us with flowers of heavenly scent and bright, beautiful spring, summer, and autumnal color. Finally, wildlife and songbirds are often attracted to their flowers and fruit -an added benefit to the environment, and to the people who benefit from the entertainment that they provide.

Four Rules for Using Ground Covers:

The uses of ground covers are nearly endless, and are limited only by your imagination. Even so, you should always attempt to follow the four basic rules of ground cover use. Adhering to these four rules will prevent the use of inappropriate or incompatible ground covers and will insure optimal success.
  1. Combining too many different types of ground covers in the same landscape results in a busy, cluttered appearance. To create the most appealing landscape, use only one or a few selected varieties.

  2. In general, plant large-leaved ground covers when the scale is large, and small-leaved ground covers when the scale is small. By following this rule, you will create a harmonious setting, and your plants will always be in the proper proportion to the landscape. Doing the opposite will waste the precious little space of the smaller landscape or leave the large setting looking naked.

  3. Sensitivity to companionship should be exercised when combining ground covers with other plant types, such as trees or shrubs. In other words, you should only install plants which will comfortably coexist. Such plants should possess not only similar cultural requirements, but complementary colors, textures, forms, and sizes. If plants of different compatibility (companionship) are planted together, not only will harmony be lacking, but extra maintenance will be required.

  4. Never combine ground covers that have incompatible growth habits. The worst offense in this regard is to combine a species of vigorous, horizontal spreading habit (such as English ivy, periwinkle, goutweed, or fleece flower) with a species of diminutive or refined habit (such as stonecrop or germander). The vigorous plants will soon overrun the smaller, slower growing ones.

Planting and Maintenance of Perennials and Ground Covers:
Even though ground covers are unique low maintenance plants that will help you to further enjoy your landscape, in order to perform their best, they will need some help to become well established. Here is what you must do: first, plant them properly; second, give them proper care. If you do these two things, your ground covers will fill in rapidly and provide maximum enjoyment with little work or expense. Planting and Maintenance:

When to Plant:
Grown Earth Friendly® plants from Hortech may be planted anytime the ground is not frozen. In early spring, if you expect frost, you may want to request plants that are still dormant- this way if there is frost, the tender new growth won't be frozen back. During summer, it is wise to water your new plants frequently enough to keep the soil moistened, until root establishment. And, during fall (maybe with the exception of English ivy), you may plant essentially up to the day the ground freezes solid. Mulching is always a good idea, and will prevent the freezing/thawing action of the ground from disturbing newly planted ground covers.

Preparing the Planting Site:
Before planting, first remove all existing grass and weeds. This includes the roots as well as the above ground parts. There are three ways to accomplish this and they are outlined as follows:

Method #1.
Black plastic mulch can be pinned on top of the site with rocks, bricks, or soil as a means of destroying weeds or turf. The principle behind this is that the combination of darkness and heat will destroy the underlying weeds. Darkness works by making it impossible for plants to manufacture food through photosynthesis, and the sun hitting the plastic causes the weeds and soil below to become very hot. Literally the combination of sun and black plastic creates an opaque solar oven that causes destruction of the weeds. This method works best in locations exposed to direct sunlight, and works better in summer than spring or fall. In general the plastic should be left in place for 2 months. Later, the site may be rototilled or spaded to loosen and aerate the soil before planting.

Method #2.
Herbicides may also be used to destroy existing turf or weeds. Herbicides work quickly and although there are a number of different herbicides available, those which work best are absorbed into the plant and translocated throughout its sap stream. These types of herbicides (such as Roundup) kill the root system as well as the top growth- absolutely essential to effective eradication since most weeds are capable of coming back from their roots. Once the herbicide has killed the turf or weeds, rototill or spade up the area to loosen the soil. Consult your local garden center for recommendations as to the best herbicide to use.

Method #3.
The final method involves repeatedly rototilling or spading the planting site until all vegetation has rotted and been converted into soil (by decomposers including fungi, bacteria, and earthworms). Typically three or four turns of the site over the course of five to six weeks will accomplish this objective.

After killing the weeds and loosening the soil, spade or rototill in any necessary amendments such as leaf mold, lime, peat moss, organic compost, or topsoil. Amendments enhance the soil's fertility, change its texture, or alter its chemical properties (such as pH), so that it is suitable for a particular plant. Amendments should be worked into the top 8 to 12 inches of soil and followed by the final grading- usually performed with a hand rake.

Planting Your Perennials and Ground Covers:
When planting, the soil level at the base of the ground covers should be the same as it was in the containers prior to transplanting. Therefore, if the containers are 3 inches deep, the planting holes should also be 3 inches. If the holes are too deep, the stems will be covered with soil and may rot. On the other hand, if they are too shallow, the roots will not have enough soil contact for adequate anchoring or water absorption. Use a tool such as a spade, trowel, or hoe to dig the holes for planting. Following planting, be sure to water your plants in thoroughly, then follow by topdressing the exposed soil between them with a 1 1/2 to 2 inch layer of wood chips. This not only helps exclude weeds but reduces the amount of watering that will be needed, cools the soil, and by insulating it, prevents the ground from heaving during late fall and winter.

Spacing the Plants:
Perennials and ground covers need to be spaced at an appropriate distance so that plantings will be easy to maintain and so that all areas of the planting fill in at the same rate. To calculate the number of plants needed, use the chart on the following page or our Quantity Calculator. This chart should be used with the recommendations for each plant (found next to the container size for each plant). Spacing is based upon rate of growth and mature spread. In general, these recommendations will allow your planting to fill in and become completely established in 1 1/2 growing seasons. Planting at the closest recommended distance may speed this to 1 season, and the farthest recommendation may extend it to 2 seasons. Of course the rate will vary somewhat with soil fertility, maintenance practices, irrigation, and climate.

Maintaining Perennials and Ground Covers:
One of the greatest advantages of ground covers is that they require little maintenance, especially in comparison to turf grass. However, to believe that no maintenance is needed is a misconception. As with other plants, ground covers may need periodic watering, weeding (at least until established), and fertilizing.

Watering Perennials and Ground Covers:
Thoroughly watering your plants immediately after planting is the first item on the maintenance schedule. This lessens the degree of transplant stress to the plants. Until the roots become well established, new plantings should be watered frequently so as to keep the soil constantly moist- but not saturated. Three months is usually an adequate period for root establishment. From then on, water as follows:

Water during the early morning so that the foliage can quickly dry. Water to the extent that the soil becomes moistened through the entire root zone (6-12 inches deep), and only when there is a genuine need, evidenced by a slight wilting of the leaves at midday.

Typically, little or no supplemental watering is necessary after the first year. If it is, it is usually only during extended hot, dry summer days. It is also a good idea to water thoroughly in late fall before the ground becomes solidly frozen. This enables the plants to better cope with winter's harshness. When plants enter winter without drought stress, they come through in much better condition.

Controlling Weeds in Perennials and Ground Cover Plantings:
The most critical step in weed control occurs before the plants are ever placed in the ground. Completely eliminating all weeds (including their roots) before you plant is essential to the rapid establishment of ground covers. Mulching after planting helps to keep weed seeds from germinating and becoming established. In time, as the ground covers fill in and outmuscle the weeds, the need for weeding will taper off, and eventually little or no weed control will be required.

During establishment, ongoing weed control can be accomplished in three ways. The first method is manual hoeing or hand pulling. Consider it an opportunity to relax and be reflective: weeding is good for your body, takes little mind power, and produces little stress. The second method is through the use of preemergent and postemergent herbicides. Preemergent herbicides prevent weeds from becoming established. Postemergent herbicides kill weeds after they have come up. They must be used carefully as they may also kill your ground cover, if you happen to spray it as well. The last and most preferred method is periodic mulching around your ground covers with organic materials. Simply resupply 1 to 2 inches of wood chips or bark as the initial mulching thins and decomposes. Mulching does not kill established weeds but helps prevent weeds from becoming established. Also, as they decompose, organic mulches help to supplement the soil's fertility.


Plants needed per: Square feet
per each
3 16.00 1,600 16,000 0.06
4 9.00 900 9,000 0.11
5 5.75 575 5,750 0.17
6 4.00 400 4,000 0.25
7 2.93 293 2,930 0.34
8 2.25 225 2,250 0.44
9 1.78 178 1,780 0.56
10 1.44 144 1,440 0.69
12 1.00 100 1,000 1.00
14 0.73 73 730 1.37
16 0.56 56 560 1.78
18 0.44 44 440 2.27

Fertilizing Perennials and Ground Covers:
Many ground covers benefit from one or two annual fertilizer applications. A general fertilization program should include the use of an organic or slow-release fertilizer. Organic fertilizers are essentially those which have come from the digestive tract (organs) of animals (i.e., horse-, chicken-, turkey-, cow-, and even human-manure, as in the case of Milorganite, the product which comes from the Milwaukee sewage treatment facility). Slow release fertilizers are chemical fertilizers that gradually release nutrients to the plant. Low-grade, soluble fertilizers (non-slow release types) are less expensive but can wash through the soil before the plant can use them completely. Because of this they are more likely to contribute to groundwater contamination, and therefore should be avoided. The ratio of nitrogen, phosphorus, and potassium in the fertilizer should be about 2-1-2, such as a 10-5-10 formulation, and it should be applied at the rate of 1 pound per 100 square feet, first in early spring and then again in early fall. A more precise custom fertilizer program can be provided by your garden center or county extension agent. This involves sampling the soil during early spring and tailoring the fertilization program to the exact needs of your particular plants and soil. Fertilizers should only be applied when the leaves of the plants are dry, otherwise spotting or rotting may occur. Following the application, use a fast stream of water to wash off any fertilizer that has adhered to or become trapped in the leaves.

Leaf Removal:
Leaves should only be raked up or vacuumed when they smother and mat down the ground cover. If the plant is of such habit that the fallen leaves slip through its canopy, then allow the leaves to remain and decompose to supplement the soil.

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