Just as the addition of a colorful bow dresses up a gift, both mulch and perennial ground covers can add the finishing touch to garden beds. When used to cover bare soil, both mulch and living ground covers discourage weeds, control soil erosion, and stabilize soil temperature and moisture. The advantage of one over the other comes when considering that mulch must be reapplied regularly, and ground covers, once established, reproduce themselves and need only periodic attention to thin or control some that wander. Often, it’s the final vision the gardener has for the landscape that  will determine which to use.

Ground cover types range from slow growers to ones that are true invasives. Slow growers include several varieties of shade tolerant phlox such as the creeping phlox (Phlox stolinifera), and the woodland phlox (Phlox divaricata).  The moss phlox (Phlox subulata) enjoys sunny spots as does candytuft (Iberis sempervirens).

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Moss phlox-bugwood.org photo

Candytuft John Ruler University of Georgia Bugwood.org

Candytuft photo by John Ruler University of Georgia Bugwood.org

If you are an impatient gardener, moderately speedy popular plants include sweet woodruff (Galium odoratum), spotted dead nettle (Lamium maculatum), wild ginger (Asarum canadense), and Chinese astilbe (Astilbe chinensis var. pumila).  Each of these plants prefers shady areas for best growth, and they generally do well in moderately moist, fertile soil.

Other moderate creepers that do well in part-shade to sunny locations include bugleweed (Ajuga reptens), low growing sedum, such as Sedum rupestra, periwinkle/myrtle (Vinca minor), and creeping thyme (Thymus praecox). These plants prefer moderately moist soil except for the thyme, which prefers a somewhat dry soil.

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Ajuga

This group of plants also includes the familiar pachysandra (Pachysandra terminalis). It grows by rhizomes that form stems that spread underground, producing roots that send up new plants. In ideal growing conditions it can be aggressive but can be controlled by removing the roaming underground rooted stems by hand.  It grows in partial and full shade as well as partial sun, but full sun causes poor growth. It needs a moist, well-drained soil and does not tolerate drought.

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Pachysandra under trees and shrubs

A group of plants that should be avoided in home gardens includes those that are very aggressive growers. One in this group, goutweed/bishop’s weed (Aegopodium podagraria), is on the Connecticut Invasive Plant List. It is said to need a mechanical barrier surrounding it to prevent it from wandering beyond its intended space.

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Variegated goutweed

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Goutweed- green leaves

A plant of similar aggressive habit, gooseneck loosestrife (Lysimachia clethroides), required hours of work to remove a mature patch –  little volunteers are still popping up weeks later! While attractive when massed in open spaces, it is so aggressive that “Perennial Gardens” author Allan Armitage wrote that the right place for this plant “happens to be an island bed surrounded by concrete.”  Two plants also bearing the loosestrife name, garden yellow loosestrife (Lysmachia vulgaris), and purple loosestrife (Lythrum salicaria,), are included on the Connecticut Invasive Plant List and cannot be sold in the state.

Sometimes mulch is the preferred ground cover. If a perennial bed has plants with attractive foliage or flowers that deserve attention, or where it would be hard to provide needed moisture, mulch can be a good option.

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Natural cedar mulch

Mulch can be organic, from shredded tree products, straw, salt march hay, dried grass clippings, compost, or pine needles. To be effective at slowing weed growth, helping retain soil moisture and moderating soil temperature, organic mulch must be replaced regularly.  However, it is not necessary to remove older mulch before adding a new layer. Often older mulch develops a crust-like surface so it should be loosened with a rake or other pronged tool so water will penetrate the surface. Some prefer using a color-treated mulch, which is not harmful to plants since the color comes from vegetable dyes.

Some problems that can come from using organic mulch include making the layer thicker than 3 inches, which prevents water and oxygen from penetrating the soil, and putting the mulch too close to the base of shrubs and trees, which encourages snails, slugs, burrowing animals and wood boring insects to settle in.

Inorganic mulch includes crushed stone, gravel, black plastic or landscape fabric. Depending on the choice of material, inorganic mulches have various advantages and disadvantages. Some allow water and oxygen to penetrate the barrier and keep weeds from breaking through. Some last for many years but some break down when exposed to sunlight and don’t allow water and oxygen to penetrate. Some are inexpensive, and others are expensive.  Budget can be a deciding factor.

When it comes to choosing between use of a living ground cover or a type of mulch, the final decision depends on the reason for using the ground cover, how much energy the gardener has to maintain the ground cover and even what image the gardener wants to project for the garden beds. In the end, the choice should consider how the ground cover will benefit the plants that are growing in the garden.

Jean Laughman, UConn Home and Garden Education Center

The Home & Garden Education Center has received an abundance of inquiries related to Japanese pachysandra, (Pachysandra terminalis) during the last few weeks. Homeowners all over Connecticut are experiencing difficulty with this groundcover. It first becomes noticeable as other things around it start to green up in the spring and we see that the leaves are remaining a sickly shade of yellowish-green.

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Affected bed of pachysandra

As it catches our attention we notice that the plantings in general look a bit sad and sparse. A closer look at the leaves will reveal that there are areas of irregular brown blotches that have concentric line patterns within the affected area and pretty sharply defined darker brown edges. The center of the spots will can appear much lighter if the salmon-pink fungal spores are present.

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Pachysandra leaves showing signs of Volutella blight

The browning areas will continue to spread and darken and can encompass the entire leaf as it dies. The cankers that can develop on the stems and stolons can girdle the stem and cause the plant to wither and die by disrupting the transport of water and minerals through the plants vascular system.Unfortunately this can happen in as little as two weeks, especially if the weather is wet and humid. It has certainly been wet over the last week and although the total precipitation is around the average 1” needed for growing plants it has come in a slow but steady sprinkle allowing plants little time to dry out between the showers.

This is all the work of the fungus called Volutella pachysandricola, or Volutella Leaf and Stem Blight. This fungus is considered an opportunistic pathogen that attacks weak plants. It can infect leaves, stems, and stolons and is considered the most destructive disease of pachysandra. The pink spores that appear in the spring will darken to reddish-orange in the late summer and fall when a second type of spore is produced.

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Close-ups of the Volutella damage and spores

This winter may have provided the perfect storm needed by Volutella to thrive. Drying winds and winter sun can desiccate pachysandra if there is not an adequate cover of snow to provide protection. Also, many beds of pachysandra are near roads and sidewalks where salts may dry them out further. A cover of mulch could provide just enough needed winter protection for plantings in these areas but it should be removed in the early spring. Some symptoms of winter injury or sunscald such as tan or scorched leaves may initially appear to be Volutella but they will not exhibit the characteristic concentric lines of the disease.

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Those same pachysandra beds that are near sidewalks or roads or are used as edgings can receive damage from mowers, clippers and weed whackers (Or as they are called in Australia, ‘whipper snippers’. I just love that!). Cuts from lawn equipment can provide an opening in plant tissue and when the plant is wet the fungal spores are able to infect it easily and travel to the stems where they will cause the girdling mentioned earlier.

Good sanitation practices can be helpful when dealing with pachysandra blight. It is too late for a good fall cleanup now but you can still remove any plant debris that remains. During dry weather remove and bag (not compost) any diseased plants to reduce the inoculum. Thinning out beds will also help improve the air circulation that can speed up drying. Fungicides can be used as preventives for new growth or when wounds occur and systemic curatives can be used when symptoms first appear although they will not correct damaged tissues. Allegheny pachysandra (Pachysandra procumbens) can be less susceptible to the disease or you could consider another groundcover such as creeping myrtle or vinca.

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Vinca major, also known as variegated greater periwinkle

Another source of wounds to pachysandra that should not be overlooked in insect damage. Scale insects such as Euonymous scale, two-spotted spider mites, and root knot nematodes have been found on plant samples that have come in to the Center. Horticultural oils and insecticidal soaps applied now can help control scale, just be sure to thoroughly coat the pests with the product. A miticide can be used on the spider mites but there is currently no control chemical treatment for the nematodes.

Euonymous scale

Euonymous scale image by Joan Allen

If you are experiencing these symptoms in your pachysandra beds you can get additional information from the Connecticut Agricultural Experiment Station fact sheet entitled Volutella Blight of Pachysandra, on our website at Pachysandra Leaf and Stem Blight, or by contacting us at the UConn Home & Garden Education Center.

-Susan Pelton