Space most ground cover 12 to 18 inches apart so the plants knit together by the end of the third growing season. The right ground cover spacing depends on how wide each plant spreads when mature, so check the label first. The goal is simple. You want the mats to just touch by year three, with no bare soil left to show through.
I knelt on the front bank one cold April in zone 5. I set out creeping phlox plugs in offset rows so the gaps between them would close even on all sides. The first summer looked sparse and I worried I had spread them too thin. By the second summer the rows started to blur together. By the third July you could not see one plug end and the next begin, and the whole bank ran purple in bloom.
When people ask how far apart ground cover should go, they really want to know the catch. Closer spacing fills in faster but costs you more plants up front. A bank that needs 40 plugs at 18 inches might need 70 at 12 inches, so the price climbs quick. Wider spacing saves money but leaves bare dirt longer, and bare dirt grows weeds. You also water and weed that open ground for an extra season before the plants take over. Full establishment can take up to two years either way, so plan for some patience no matter which spacing you pick.
Here is the technique that gives the quickest and most even cover. Plant in a staggered, offset pattern instead of a straight grid. Set the second row half a space over from the first, so each plant sits in the gap of the row behind it. The runners then reach into open ground from every side at once. A grid leaves square holes that take an extra season to close. I learned the offset trick after my first bed went in as a plain grid and stayed patchy through its second summer. The next bed I staggered, and it closed a full year sooner with the same number of plants.
Slopes and erosion-prone spots are the one place I push spacing tighter. On the front bank I used 12 inches instead of 15 because I wanted roots holding the soil before the next heavy rain. Flat beds with good mulch can go to the wide end of the range and still look full in time. Sun matters too. A plant in full sun spreads faster than the same plant in shade, so shaded beds earn slightly closer spacing. The same goes for fast spreaders like creeping jenny or vinca, which can take wider gaps than a slow grower like creeping thyme.
One small trick keeps every gap even. Cut a stick the length of your spacing and lay it down between plants as you go. A folding ruler works the same way. This beats eyeballing and stops the slow drift that leaves some gaps wide and others tight. Even spacing is what makes a bed close into one smooth mat instead of a lumpy patchwork.
Good ground cover plant spacing starts with one number off the tag. Find the mature spread, then space the plants so the edges of those mature mats will just meet by the third season. Mulch every gap with two inches of shredded bark right after you plant. The mulch blocks weeds in the open soil and holds moisture while the runners stretch out. Pull the few weeds that do sneak through by hand, since one missed weed can claim a whole gap before your plants do. Water deep once a week through that first season, and your spacing will look right on schedule.
Read the full article: Flowering Ground Cover: 12 Best Plants
