The time to plant a ground cover varies across the country. In warm areas, ground covers can be planted almost anytime, if water is available to see young plants through their establishment period. Generally, either spring or fall planting is best. These are the times of least environmental stress, when the shock of transplanting is most easily endured, temperatures are moderate, and rainfall is most abundant.
In cold-winter areas, spring is usually more successful. Fall plantings are more likely to be heaved from the ground by the alternate freezing and thawing of the soil. Young plants may literally be pushed out of the ground. With their roots exposed, they quickly die. If you must plant in fall in a northern climate, do so as early as possible to allow the young plants time to become established.
Where freezing soil is not a problem, fall planting allows the plants to use winter rains and cool temperatures to become adjusted to their new site. When spring comes, the plants are already established and begin to cover the ground more quickly.
In areas with dry summers, avoid planting after late spring unless you are prepared to spend a lot of time watering.
Before any planting begins, it is essential that all established perennial weeds, such as quackgrass, bermudagrass, and bindweed, be eliminated in areas where ground covers are to be planted. Weeds that are not killed will come back. They will compete with the new plants for nutrients and may even crowd them out. Removal is much more difficult after ground cover plants are in place. Use a systemic weed and grass killer, to remove any existing vegetation before planting. Carefully follow all label directions.
Amending the Soil
Ground covers are plants that naturally grow very close together, creating heavy competition for nutrients and water. Starting with good soil helps the plants to thrive in crowded conditions. Soil for ground covers should be prepared as carefully as for a lawn. Extra effort in readying the soil often makes the difference between success and failure.
For proper growth, plants need air in the soil, sufficient moisture, and a supply of mineral nutrients. Clay soils hold nutrients adequately but drain too slowly and leave little room for air. Sandy soils are well aerated but lose moisture and nutrients too quickly.
The best way to improve either sandy or heavy clay soil is through the addition of organic matter. Adding organic matter, such as compost or manure, loosens clay soils, allowing air into the soil and making it easier to work. When added to light sandy soil, organic matter holds moisture and nutrients in the root zone.
The quantity of organic matter must be large enough to physically alter the structure of the soil. This means that about one third of the final mix should be organic matter. In planting terms, this would be a layer of compost or manure at least 2 inches thick spread over the planting area, worked into the soil to a depth of 6 inches.
When ground covers are being planted closer together than about a foot, as they are from flats and cell-packs, prepare and till the entire bed. With larger plants, as those from gallon cans or ball-and-burlap, it’s usually simpler to dig individual holes and amend each plant separately.
In addition to amending the soil to ensure adequate drainage, add a controlled-release fertilizer when planting. Stir some Osmocote into the soil in each planting hole, following label instructions, or drop a Miracle-Gro Tree Spike into the hole with larger plants. These slow-release fertilizers will release a steady flow of nutrients throughout the entire growing season.