There is no better way to fill-in large garden areas quickly than with the right mix of spreading plants. When gardeners have a lot of terrain to cover and are looking for a low maintenance, inexpensive way to do it, they head to the groundcover department at their local nursery. There are plenty of groundcovers that will form a dense mat of vegetation in either sun or shade in just a growing season or two—the only problem is that many of those plants are also found on lists of the most invasive species throughout the country. Rather than plant something that is known to spread where it is unwanted (and become next to impossible to eradicate), choose from one of the more well-behaved—but still fast-growing—species below.
Yarrow is one of the few groundcovers that tolerate foot traffic almost as well as a lawn. The 6-inch tall ferny foliage spreads quickly, whether you plant it by seed or groundcover plugs, and the 12 to 18-inch tall flowers—which come in colors ranging from white to yellow to crimson red—are a feast for the eyes, as well as for butterflies, throughout the summer. This sun-lover thrives in USDA zones 3 to 10.
Ajuga thrives in moist, partly shaded places, creeping along quickly with its spatula-shaped leaves and petite flower stalks to form a lush 4-inch deep carpet in no time. Purple-tinged varieties, such as 'Burgundy Glow', are among the most popular, creating a striking contrast with the surrounding greenery. USDA zones 4 to 10.
Alyssum is a sun-loving annual groundcover, though it can almost be viewed as a perennial because it seeds itself reliably in most regions of the country, coming up year after year to carpet the ground with its white honey-scented flowers. Use it as quick filler between larger perennials and enjoy watching it naturalize throughout the garden—but don't worry, it is very easy to pull if it pops up where you don't want it. Works in all zones.
Lamb's ear is grown for its soft, velvety foliage—just like, you guessed it, a lamb's ear—but it also happens to be a tough, fast-spreading plant capable of colonizing poor, dry soil in a hurry. It's a great choice for planting in a sunny rock garden where the 6-inch mat of foliage will soften the boulders as it fills in all around them. USDA zones 4 to 9.
Rock Rose is one of the best groundcovers for arid regions—it sprawls into a 1 to 2-foot tall groundcover, covering large swaths of sunbaked earth, even with minimal irrigation. The crinkly leaves are full of essential oils that cause them to shimmer in the sunlight and the colorful flowers (shades of pink, purple and white, depending on the variety) bloom almost endlessly during the warm months of the year. Some Rock Roses grow into shrubs, so look for varieties like 'Sunset' that stay two feet tall or less for use as a groundcover. USDA zones 7 to 10.