Trimming ground covers
Edging. If not restricted, many ground covers will advance beyond the area you’ve allotted for them. If the plant spreads by underground stems or by rooting along stems that touch the soil, you may be able to control it by trimming the planting’s edges with pruning or hedge shears or with a rotary mower. But if growth is progressing significantly out of bounds, you may have to dig out the portions that have gone too far. Installing a permanent barrier of wood, brick, stone, or concrete will save you a great deal of hand edging. To keep persistent ground covers from creeping under the barrier, check the plant’s root depth and be sure the barrier extends deeper than that distance below ground.
Pruning. Some shrubby ground covers that are normally low growing may occasionally send out upright stems that spoil the evenness of the planting; cotoneaster is one example. When you see such stems, cut them back to their point of origin or to a horizontally growing lateral within the foliage mass.
Woody ground covers–especially junipers and cotoneasters–are sometimes planted too close to paths, making frequent pruning necessary. Because constant cutting back usually ruins the shape of the plants, it’s often better simply to replace them with more suitable plants.
Mowing. Ground covers that root as they spread, as well as those that spread by underground stems to form dense patches, may eventually become so thick and matted that only mowing will restore their good looks. Plants like ivy (Hedera) accumulate thatch beneath the foliage; others, such as winter creeper (Euonymus) and Aaron’s beard (Hypericum), may become rangy and untidy. Mow these ground covers just before the start of the growing season, using a heavy-duty power mower set at 3 to 4 inches. Then fertilize to encourage rapid new growth.