Ground covers that are spaced closer together than two feet should be watered with a sprinkler system or with low-pressure mini-sprinklers. Plants spaced farther apart and those on steep slopes are most efficiently watered with a drip irrigation system.
Young plants should be given special watering attention. A steady watering program is important so that root systems develop fully. Watch the plants and make sure that water is getting to the roots. After the plants are growing, adjust the watering program to one of deeper and less frequent watering. This causes the roots to penetrate farther into the soil. Plants then become firmly entrenched in the ground; in a drought situation, this could make the difference in the survival of the ground cover.
Check the soil to make sure that adequate moisture is being made available to the plants. To do this by hand, dig down to the root depth (6 to 12 inches) and withdraw a handful of soil. If it will not form a ball, it is most likely too dry. If it forms a ball that doesn’t crumble easily, it is probably too wet. (Although sandy soil crumbles even when it is very wet.)
Another way to test the soil is with a moisture meter (available at nurseries and some hardware stores). Choose one with a long probe for outdoor use.
A slope, particularly one without mulch, is more difficult to water than a planting in a level area. Erosion poses a constant threat. Create small terraces around each plant or terraces across the width of the slope to help control runoff. If erosion occurs, apply the water more slowly. Drip systems are excellent for watering slopes because they apply the water so slowly that runoff cannot occur. Mini-sprinklers also can be used. Another method is to leave the sprinklers on for 10 minutes (or until the water starts running off) and then off for 20 minutes, giving the water time to soak in. Repeat this until the soil is thoroughly wet.
Where water is scarce or limited, or rainfall is seldom sufficient for even established plants, drip irrigation offers the most efficient way to use and apply water, especially for shrublike ground covers.
Basic systems are inexpensive and easy to install. Although they can be put in place after planting, it is easier to put the system and plants in at the same time. Installing a drip system involves assembling a series of hoses, lines, and emitters or porous tubing that will deliver moisture slowly to plant roots. These can connect with a garden hose or faucet.
Drip irrigation waters only the roots so that a minimum amount of water is lost through evaporation. There is less problem with diseases spreading from splashed or wet foliage, and there is no runoff or soil loss because the soil is soaked very slowly. Drip irrigation is ideal for slopes where water applied by other methods often tends to run off before it can sink in.
Basic drip-irrigation kits for small areas are relatively inexpensive. Check the supply sections of garden catalogs or look for companies that specialize in such systems. Their catalogs contain basic information on buying, installing, and maintaining various systems. Drip systems can be automated with timers, and fertilizer injectors can be added to allow feeding and watering in one simple operation.
Drip-irrigation systems can lie on top of the ground or be covered with a few inches of mulch or soil. Place the tubing 12 to 18 inches apart for small plants, 12 inches apart on slopes and in sandy soils. Where temperatures drop below freezing, plastic systems must be taken up before the first frost and the parts drained and stored indoors, as with any hose. Systems with piping made of PVC (polyvinyl chloride, a plastic material) can be thoroughly drained and left in place.
Drip systems are not as practical for closely spaced plants or those that form a solid mass of root or leaf cover, such as Aaron’s-beard (Hypericum), English ivy, periwinkle (Vinca), and some cotoneasters. For these an underground PVC pipe with fixed sprinkler heads on risers elevated just above the foliage will moisten all the soil beneath.