Winter is a good time to check the garden for large bare-soil areas that would benefit from ground-cover plantings. Areas with chronic weed problems or where existing ground cover is struggling are also candidates. So are areas where moss is taking over lawn. Note the soil, light and weeds that are present, and then look through garden publications for plants that match the growing conditions.
Aside from standard ground covers, some hardy low-growing shrubs may fill the bill: Siberian cypress (Microbiota decussata, a Great Plant Pick), dwarf Japanese spirea (Spiraea japonica 'Nana'), prostrate junipers, Rhododendron 'Ruby Hart,' Stephanandra incisa 'Crispa' or ground-cover roses.
In USDA Zones 4-6, wait to plant until soil warms up, but in Zones 7-9 (most of Portland is Zone 8), planting of woody ground covers can begin during winter when temperatures are in the 40s, as long as the soil is not too wet. For herbaceous plants, start in early spring, or plant throughout the growing season as long as you provide mulch and water.
NEW GROUND COVER
The number of plants you need for a ground cover depends on the size of plants (flats, 4-6 inch pots, 1-gallon or No. 1 containers), growth habit and growth rate. Here's how to plan for a new area.
1. Prepare the area by removing weeds and mulching thickly with 4 inches of coarse organic material. This can be done weeks to several months before planting.
2. Measure the area. Then calculate the number of plants to fill it at the desired spacing. One hundred plants such as Ajuga or strawberry set 8 inches apart should cover about 44 square feet. A spacing of 18 inches for woody plants such as 1-gallon cotoneaster covers 225 square feet.
3. Use a triangular grid to provide equal spacing in all directions. Make a template of cardboard or bamboo stakes for large areas. Plan to add filler plants in the second year.
4. Plant through existing mulch by scooping away enough to expose a bare patch for each spot. Water in if needed.
5. Water smaller plants more frequently than larger transplants. Fertilize lightly during the first year or two. Weed new plantings three to four times a month during the first growing season. The frequency will slow as plants fill in.
-- HGNW staff
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