Maintaining ground covers

Whether they are complementing turf and mulches or supplanting them, ground covers can provide a spectrum of colors, textures and forms to enhance any garden or landscape. Responsibility for maintaining vigorous healthy ground covers falls on the landscape designer and the maintenance personnel who will care for the cover.

For ground cover to fulfill its potential, the landscape design must take into account soil quality, light, space and other site challenges. And the workers responsible for maintaining the planting must be aware of the designer's intent, or their efforts may be counterproductive.

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Defining ground cover In his book, Ground Covers in the Landscape (Sierra City Press, 1982), Emile Labadie defines them broadly: "Plants that grow up to a height of from several inches to 3 feet and that spread over the soil area are considered to be ground covers."

Some ground covers are grass-like and even can handle limited traffic, such as Mondo grass (Ophiopogon japonicus); some are vines allowed to grow prostrate on the soil, such as Bougainvillea (Bougainvillea spectabilis) and ivies (Hedera spp.); others are low-growing shrubs, massed to provide a vegetative continuum, such as Australian fuchsia (Correa pulchella) and 'Ballerina' India hawthorn (Rhaphiolepis indica 'Ballerina').

The Santa Cruz Ground Cover Nursery (Santa Cruz, Calif.) grows nearly 65 types of ground covers, including different color forms and cultivars of the same species (such as 10 gazania cultivars).

"Basically, whenever pedestrian traffic and intensive use are not design program needs, and whenever the high water- and maintenance-need aspects of annual color and turfgrass are deemed a negative, ground covers provide an optimal plant form under trees and shrubs, or even on their own," says owner Mark Henry.

Designing for walks and edges At the request of their clients, or because they themselves can't accurately predict the eventual size of the ground cover they are specifying, many landscape designers over-plant new landscapes. Unfortunately, this means that maintenance personnel will be burdened with the intensive care of these over-packed areas. Knowing a ground cover's projected mature spread will help you maintain a more natural-appearing edge to the planting bed.

To avoid severe shearing of ground covers at edges, space the leading line of ground cover plantings at least half of their projected diameter back from the edge of a walk or boundary. If you expect a ground cover to grow 4 feet in diameter at maturity, set the ground cover back from the edge by 2 feet. At maturity, its edges should nicely fold against the border of the planting bed.

If your client is stubborn about the need to have rapid growth and coverage, you can place the ground cover closer to the walk. However, specify in the maintenance guidelines that the transitional leading-edge plants should be removed once they crowd the edge of the walk. In this way, maintenance personnel won't have to shear continually, and the ground cover can achieve a more natural appearance. The cost of removing the leading edge of the planting is easily offset by the reduced maintenance.

Preserving shrubs in ground covers Vines-such as the several types of ivy-make excellent ground covers. Unfortunately, ivy will aggressively climb into low-growing shrubs. Often, unobservant maintenance personnel simply shear the vine into the same shape as the shrub, giving the effect of some strange hybrid plant. For this reason, designers should consider ground covers other than vining types if they plan to maintain tree and shrubs in the same planting. Ivy, creeping fig and other types that attach themselves to surfaces with their 'feet' are poor choices in these situations.

Planning for leaf fall When growing ground covers under trees, you must consider the problem of fallen leaves. There are two differing approaches. Bill Holly, of Central Coast Landscape and Maintenance Inc., supervises the maintenance of acres of diverse ground covers in and around Santa Cruz, Calif. Holly feels that if you plan on removing the leaves regularly to maintain a manicured appearance, you should choose a compact, well-sheared or mowed ground cover treatment. This makes it easier to remove the leaves by raking or blowing.

If you won't be raking or mowing the bed often, groundcovers that have a more natural, uneven and open growth form may be suitable. With these types of plantings, leaf litter falls between the open branches and decomposes around the base of the plants, where it serves as an effective mulch.

Designing irrigation One of the most challenging aspects of maintaining ground covers is irrigation. Ground covers that grow above 12 inches often block sprinkler heads. The "solution" is to install unattractive riser extensions that push the head farther up into the air. You can avoid the necessity of riser extensions by mowing on a regular basis to control height.

You might think that drip irrigation is the answer to this problem. And it's true that if you plant ground covers from containers, and not from flats or bare root, drip irrigation works well for effective water placement and conservation. However, as individual plants grow into each other, lack of accessibility makes the maintenance of drip-irrigation systems nearly impossible. If a drip emitter supplying a specific plant fails, you may never know it until the plant is nearly dead. If an individual plant in a mass of ground cover dies, especially if it is a wide-spreading type, the result is an ugly hole.

In ground cover plantings, and especially along the outer edges of the plantings where sprinklers are frequently damaged, I recommend 12-inch-high spray heads (or rotors) on triple swing joints. If the PVC nipples on the swing joint are at least 12 inches long, you can slowly raise the entire pop-up head out of the ground to accommodate the growth of the ground cover. Conversely, after mowing the ground cover you can lower the swing joint back into the ground so it is less visible.

In attempting to keep irrigation heads on the outside of ground cover plantings, the designer must think about the radii for the different irrigation heads that might be used. For wider beds, rotor heads may be useful, whereas spray heads can be suitable for narrower beds.

Irregularly shaped ground cover plantings are easier to irrigate than oddly shaped lawns. Because turf needs nearly 100-percent coverage, overspray of irrigation water onto adjacent paved surfaces is a frequent problem. Ground covers, by contrast, can thrive with as little as 60-percent coverage. For this reason, triangular beds, wavy-edged beds and part-circle beds can conserve water when planted to ground covers.

A good strategy for installing a ground cover planting in an odd-shaped bed is to lay out the irrigation system and "tune" it to water only within the borders of the bed. Then plant the ground cover to the wetted areas. In this manner, you guarantee effective coverage without overspray.

Controlling growth Ground covers are versatile in non-turf areas, but only if you use good maintenance principles.

* Mowing. Most ground covers benefit from some degree of mowing every 1 to 3 years, depending on growth rate, habit and location. Holly says that he tries to mow individual ground cover beds about every other year, usually in early spring.

Different types of ground covers require different types of mowing equipment. You can mow softer, fleshier herbaceous ground covers with a lawn mower with its deck set higher off the ground, or with a spin trimmer with plastic filament line. A more heavy-duty mower, or a spin trimmer with a brush cutter, is suitable for more woody species.

Depending upon the amount of debris remaining after the mowing, you can either rake it up or leave lighter amounts on the ground to decompose and provide organic matter for plant growth. In this case, fertilizer helps organic matter decompose more quickly without taking nitrogen from the soil.

* Shearing. Depending on the form you desire and the particular species' growth habits, you can extend the time between mowings for some ground covers by shearing. One warm-climate plant that takes on a beautiful, sculpted form in warmer growing areas is lantana. You can shear the purple variety of Lantana montevidensis just before flowering, to create a topiary-like form with color swirling across the surface. Designers and maintenance personnel should also look at other species on which to use this shearing technique to create interesting forms and color variations.

Remember, however, that shearing, in and of itself, is not always conducive to plant health, and periodic heavy pruning or mowing should still be an option, even if infrequently.

Fertilizing Ground covers need fertilizer on a regular basis, generally before their growing season begins. Henry recommends a balanced granular fertilizer for best all-around growth. He uses a more expensive and more-frequently applied liquid fertilizer to give his plants more sales appeal, but acknowledges that liquid fertilizers are not always as long-lasting and cost-effective in field-maintenance programs.

Holly concedes that different ground covers have varying fertilizer requirements, He says that the general fertilization program at Central Coast Landscape consists of a granular 15-15-15 polymer-coated, slow-release fertilizer in early spring (after mowing). He also makes light applications of nitrogen thereafter, as needed. About every 6 to 8 weeks works best in Central California.

Irrigating after fertilizing helps water in the nutrients, and can prevent burning on newly emerging leaves.

Irrigation scheduling Base your watering schedules for ground covers on standard criteria-soil texture, sun/shade conditions, water needs of the species and slope.

Holly's general recommendation for irrigating ground covers is "deeply, infrequently." Outside the rainy season, he advocates no more than two irrigations per week, with one a little heavier than the other. Again, he cautions each site will have a different set of water needs, but no irrigation should result in standing water, which may cause disease.

Controlling weeds and other pests The most effective weed control takes place during a ground cover's planting and establishment. Use of pre-emergent herbicides, especially when planting bare-root or from flats, reduces germination of weeds. This is important because spraying may not be an option for remedial control due to the potential for herbicide damage to desirable plants. And with mechanical removal, you can end "throwing the baby out with the bath water" by removing young ground-cover plants along with the weeds.

Once a ground cover bed is established, specific weeds within specific plantings will require specific remedial treatments (mechanical removal vs. continued granular pre-emergence applications vs. post-emergence herbicides). Use your best judgement as to which treatment is best.

Gophers, ground squirrels and rats frequent taller-growing ground cover beds. Therefore, mowing regularly, as close to the soil surface as the particular ground-cover species will allow, can effectively control these animal pests. If animal pests persist despite mowing, other common pest controls (poisoning or trapping) may be necessary.

Holly also notes that snails and slugs can be a nuisance in some ground covers, notably gazanias and ivy, especially in the spring. He recommends granular slug and snail baits for control.

Ground covers provide effective, beautiful open space to landscapes. By effectively designing and establishing ground covers for successful growth and long life, they'll provide effective, year-round beauty in the landscape with only minimal maintenance.

Steve McGuirk is a landscape architect with the Madrone Landscape Group (Soquel, Calif.).

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