(Editor's Note: This article was originally published on March 11, 2008.Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
The advantages of mulch are well documented - they are effective weed suppressors, insulate the soil, help retain moisture, give the garden a nice, finished look, and, if organic mulches are used, they break down to improve the soil.
However, the liabilities of organic mulch are often overlooked. It is expensive in large quantities, and extremely so if one hires a landscaper to apply it. Even a healthy, three-inch layer can only be expected to last two years at most. After one season it will need to be ‘fluffed up'. It floats away in heavy rains, and if it remains wet, can attract slugs. It is often mistakenly placed against the plant base, increasing the chance of rot or insect damage because of the persistently moist condition. There is never a shortage of 'mulch volcanoes' around!
Hosta 'June' with Golden Creeping Jenny
Opting instead for a ‘living mulch', I have tried to find the right candidates for various conditions. Substituting plants means giving up some of the insulating and moisture-retaining qualities of the mulch. However, the right choice will still suppress weeds, shade the soil, save money and effort, and will provide the bonus of more plant material whose foliage and/or blooms will complement the rest of your bed design.
Before choosing possible candidates, a number of factors must be considered. How much sun does the area receive? Is it moist or dry? Ideally, you should not need to irrigate your ground cover once it is established. Another consideration is the likelihood of foot traffic. Some great plants would be ruined with the least bit. Finally, how long are you willing to wait for the plant to spread to cover the area? Some will be too slow to be effective, while others are too aggressive and would take over the garden.
Hellebore foliage forming 'canopy'
The term ‘ground cover' has come to mean many things. It has been used to describe almost any plant that stays relatively low. For example, one plant I grow and like very much is ‘Gro-Low' sumac (Rhus aromatica ‘Gro-Low'). It is often described as a ground cover. However, it has such an open form and spreads so slowly that I would never consider it as one. My quest mandates that ground covers either have a tight structure so as to choke out any weeds, or weave together to completely deny them any appreciable sunlight. I prefer them no taller than around 18 inches, and they must be virtually carefree.
Because I am interested in establishing these plants in large beds, I have not tried any mosses, thymes or similar plants that people use for ‘fillers' between pavers, etc.Stachys 'Helene von Stein' surrounds Stokesia
For shady areas that will not see foot traffic, it is tough to beat hostas and hellebores. They will take a few years to reach mature size, but planted with the correct spacing, they will provide a virtual canopy that will completely shade out any weeds. Hostas will need some extra moisture until they are established. Fragrant varieties will give that added bonus if you don't mind the tall flower stalks. Unfortunately, they are a deer favorite. Hellebores will reward you with beautiful long-lasting blooms in late winter and early spring, and the large palmate leaves provide a lush look all season. Deer don't bother with them. The hybrids I use reach about 18 inches high. They are semi-evergreen in my area so the foliage gets cut back in late winter. Other possibilities include Lamium and Galium odoratum. Ajuga is a candidate that will take foot traffic, though some have found it too invasive. Many people use Pachysandra, but it never appealed to me.
In partial sun areas with no foot traffic, I have used Geranium macrorrhizum. The cultivar I have used is ‘Ingwersen's Variety', which sports pretty pink flowers in spring. These hardy geraniums form a dense mat of aromatic foliage that slowly spreads to create an 18 inch high thicket. Over time fat rhizomes, which store moisture for use in drier times, develop at ground level. The evergreen foliage turns red in fall.Geranium 'Rozanne'
In sunny areas, Geranium ‘Rozanne' is showing great promise. It scrambles at first, but eventually forms a thick enough mat to keep weeds at bay. Its beautiful blue flowers bloom virtually non-stop in my garden from June through frost. I have not noticed any deer damage to date. It can eventually reach about 20 inches high. Another one is Stachys byzantina ‘Helene von Stein', or large lamb's ear. It has large, fuzzy, deer-resistant leaves and grows about six to eight inches tall. It forms a dense mat. The foliage does get ratty by late winter and must be cleaned up to make way for the new leaves.
There are three candidates that have proven themselves effective from full shade to full sun. The first is the commonly used Vinca minor or myrtle (or periwinkle). It is evergreen and has tiny light blue flowers in spring. It reaches about four to six inches tall and is easily rooted to make covering a large area easier. Just pop out a clump with roots and plant it. Some weeds will grow through it since it has a semi-open habit, but overall is effective at weed control. It will take occasional foot traffic and recover. The advantage of any evergreen ground cover is that it is ‘working' in early spring when weeds are already sprouting.
Golden Creeping Jenny
Another is Lysimachia nummularia ‘Aurea', or golden creeping jenny. This plant forms an extremely dense mat a few inches or less high that will stand up well to moderate foot traffic. The golden form is less aggressive than the green. It turns bright gold in sun, while remaining more chartreuse in shade. It prefers average to moist conditions and will grow well in very wet areas. I have some at my pond edge that grows right into the water. The gold color plays off darker foliage plants very well. It too is easily rooted.
Ranunculus repens 'Buttered Popcorn'
Last is Ranunculus repens ‘Buttered Popcorn', or creeping buttercup. This plant has variegated foliage that also brightens up with more sun exposure. There are negative reviews of it in PlantFiles, with members complaining it was too aggressive and was choking their perennials. I have not seen this at all so far and I have had it about four or five years now. If anything, it has not spread quickly enough for me! The straight species is reported to be much more aggressive. It stays well under a foot tall and has tiny yellow flowers in spring. The variegated leaves are deeply cut and are very attractive. Like creeping jenny, it will spread more rapidly in moist, shady conditions and roots easily. I lost quite a bit of it one winter but it has been re-establishing itself since.Geranium 'Rozanne' flower
One should always check if a particular plant is invasive in his or her area before attempting it as a ground cover. Invasiveness (spreading by runners in this context) varies by region and is greatly affected by growing conditions. It is certainly a balancing act to come up with a plant that spreads fast enough to make an effective, weed-blocking ground cover, yet does not take over the garden and bully the other plants. English ivy is certainly an example of the latter. So is Houttuynia cordata ‘Chameleon', especially in moist soil. I have some in a dry area that stays more behaved. Most mints also spread like wildfire. All are difficult to eradicate.
My quest continues, but I am narrowing the field and hope to eliminate mulch from my garden in the next couple of years. I look forward to enjoying the living tapestry that will weave its way around my garden.
All photographs taken by the author.