As the simple name implies, ‘groundcover’ covers the ground. Groundcover plants stay lower than shrubbery, and function something like mulch. They insulate shallow roots of other plants, inhibit weeds, and some groundcovers inhibit erosion. Besides all their utilitarian functions, they provide appealing foliage, and some bloom nicely.
Lawn is probably the most common groundcover, and is also the most useful; but that is an entirely different and involved topic! Other groundcover plants are spreading perennials, plants with sprawling stems, or vines grown without support. Most are evergreen, since defoliated plants do not cover much of anything too well.
Gazanias and iceplants are popular perennial groundcovers. Their old stems tend to die out and decompose as efficiently as new stems pile up over them, which is why they do not get too deep. Gazanias can eventually get bald spots that need to be patched with new plants, or ‘plugged.’
(The debris from pruning the edges of easily rooted perennial groundcovers can be processed into cuttings known as ‘plugs’, which can go directly into bald spots. Plugs can be taken from dense spots if no edging is necessary. They should be watered regularly, or plugged in autumn to take advantage of rain while roots develop.)
Groundcover forms of ceanothus (wild lilac), juniper and contoneaster are really shrubs that extend their stems more horizontally than vertically. Honeysuckle and both Algerian and English ivies are vines that spread over the ground until they find something to climb. Their stems root into the ground wherever they need to.
Since most groundcover plants are naturally understory plants that grow below larger plants, many tolerate considerable shade. Periwinkle and the ivies are remarkably happy in partial shade. However, vines, particularly the ivies, will climb walls and trees for more sunlight if they get the chance.
Many of the perennial groundcovers and some of the vines are neater if mown or cut low annually. Periwinkle does not need to be mown, but can get rather unkempt before new growth overwhelms the old through winter. Mowing eliminates the old stems, and makes the new growth fluffier. Dwarf periwinkle stays too low to mow.
Tony Tomeo 
I’ve come to really appreciate some of the flowering groundcovers I’ve learned to recognize. One of my favorites is a tiny native wild geranium with flowers only about 1/3″ wide. It’s cute as can be.
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Ground cover can be underappreciated because it is so utilitarian. Some of the iceplants (besides the ‘freeway’ iceplant) can be spectacular in bloom. It is not native, but it used to be very common on hillsides below hillside homes of Southern California. It showed up as magenta, red or pink squares on the hillsides below a row of houses.
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Ground cover is great as long as it can be kept in control. I’ve made a few mistakes.
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English ivy that was imported as a ground cover happens to be the worst of the aggressively invasive exotic species here. It is not so bad elsewhere in California, but is horrid in the redwoods.
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Here in south central Pennsylvania we stopped commercial lawn treatments 3 years ago on our half acre. We pull weeds in the deep garden beds, apply mulch and water as needed. We tote good rich soil in each spring, plant more perennials, sow Eden’s wildflower seeds, so our flower beds continue to expand. We keep an eye out for grubs but so far, so good. We mow the lawn only every ten days or so. Large patches of white clover now. It re-tops with white flowers few days after mowing. And we like how that looks – as if yards of our childhoods. What do you think? Is this a sensible plan here in suburbia? ps birds & worms galore! We made habitats and hatched mason and leaf cutter (bee) pupae to join other types of bees we already had.
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In your region, it is probably practical. It would not work in a drier climate. Even with irrigation, clover gets rather crispy through summer. Clover is more of a cover crop than a ground cover, although it can work the same way. There are no rules for such applications. If it works, then it is a matter of preference. If you happen to like it, ans suburban neighbors do not mind, than it is fine.
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I’m getting more interested in low-growing sedums and sedges as ground covers.
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Sedums live there?! I would expect them to succumb to frost.
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There are hardy Sedum: spectabile, S. kamchaticum, S. ternatum, etc.
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Sedum spectabile is a ground cover, or does it just cover a blot of ground when it mounds out?
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Actually I don’t think of S. spectabile as a ground cover, too tall.
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It is a new one for me. It is nice how it fills in where weeds would otherwise dominate, but then dies back for winter, which is odd for sedums here.
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