Think outside the littleleaf boxwood

By Heather Kirk-Ballard

LSU AgCenter Horticulturist

Littleleaf boxwood (Buxus microphylla) is a thick evergreen shrub native to Japan and heavily used in landscapes all over Louisiana as a low hedge planting, in mass plantings and as a foundation planting around a house. Boxwood has been used extensively in formal gardens for centuries to create lines and shapes and as a frame that leads the garden visitor from one area to another.

Boxwoods have been noted in recorded history since 4000 B.C. when the Egyptians first used them as hedges in formal gardens. They then came to North America from Europe and Asia in the mid-1600s during the Colonial times to duplicate the hedges of formal gardens. The American Boxwood Society calls it “man’s oldest garden ornamental,” and the National Boxwood Collection at the United States National Arboretum in Washington, D.C., houses the most complete living collection of boxwoods with more than 350 unique boxwoods from 180 categories. They’re a big deal and have been for some time.

These plants have been used extensively because they are dense, thickly branched evergreen shrubs that can be trimmed to create interesting shapes for hedging and for topiaries. They sport leathery, glossy opposite leaves of medium green. Dwarf forms are commonly used, but when left alone some can grow up to 10 to 12 feet tall.

They grow best in moist, cool soils with full to partial sun exposure. Boxwoods are shallow rooted, so it’s important to mulch around the roots. Because the shrubs have a slow growth rate, they require some nurturing for establishment. Protect them from heavy winds, cold and heavy sun when first established. Be sure to water them well in the first few weeks. Be aware that they can have foliar damage in extreme cold.

Many cultivars are available, including Compacta, which is very small and compact; Green Gem, with dark green foliage; Green Mountain, which has a moderate growth rate, conical form and small leaves; Winter Beauty, a mounded form with dark green leaves that bronze in winter; Koreana, which is compact, cold hardy and more spreading with dull green leaves; Sunnyside, which has larger leaves with good cold hardiness and is fast growing with some bronzing in the winter; Wintergreen, which has small, bright green leaves. And these are just a few.

Boxwoods have their issues. They are loved by spider mites, leaf miners and psyllids. They are also susceptible to plant diseases such as macrophoma blight, phytopthera root rot, and volutella blight. And then there is the dreaded boxwood blight disease. First seen in the United States in 2011, this fungal disease is caused by Calonectria pseudonaviculata. The plant will display brown lesions on the leaves, and brown or black cankers will appear on the stems. This will lead to defoliation and possible death if not addressed. Once infected, there is no cure. Fungicides may reduce the chances of infection. Other practices include proper spacing, watering at the base of the plant to keep leaves dry, removing diseased leaves, sterilizing pruning equipment, and rotating fungicides to avoid resistance. Sounds exhausting, right?

Another major concern with boxwoods was first described by LSU AgCenter plant pathologist Raj Singh in 2015. The disease is called boxwood dieback, which is caused by the fungal pathogen Colletotrichum theobromicola. The disease causes foliage and branches to die back, leading to the trademark tan foliage that stays attached to the branches. An additional symptom is black discoloration of the stem underneath the bark that you can see when the bark is scratched back.

Just like boxwood blight, the disease is spread by spores from the plant to the soil and onto other surrounding plants. It is also spread by infected pruning equipment, rain and irrigation water droplets. Because it is such a new disease, fungicide treatments are limited.

We recommend a preventative approach by using plants that are not susceptible to the disease but can still help you achieve the same look and design in your landscape.

Some great boxwood look-alikes are readily available to you. Dwarf yaupon holly (Ilex vomitoria) and inkberry holly (Ilex glabra) are both native plants and therefore adapted to our climate. And they’re susceptible to disease and insect pests.

You can also try other evergreens with coarser-textured leaves that can be shaped as hedges. These include distylium (Distylium x), dwarf arborvitae (Thuja sp.), podocarpus (Podocarpus macrophyllus Maki), wax myrtle (Morella cerifera Don’s Dwarf or Tom’s Dwarf), Carissa holly (Ilex comuta Carissa) and pittosporum (Pittosporum tobira Wheeler’s Dwarf) to name a few.

As always, think outside the box — or in this case, outside the boxwood. I don’t want to discourage you from using this classic shrub that has been used for centuries. But I am suggesting interesting alternatives for a time when these disease issues are a real concern. As plant pathologists continue to research the disease and come up with cures, plenty of alternative evergreen shrubs can be hedged and trimmed for formal settings. If you can imagine it, you can find the plant to fulfill your vision.

Littleleaf boxwood is susceptible to many things in early establishment including many fungal diseases that can lead to death-photo credit Heatther Kirk Ballard.jpg thumbnail

Littleleaf boxwood is susceptible to many things in early establishment, including many fungal diseases that can lead to death. Photo by Heather Kirk-Ballard/LSU AgCenter

Boxwood dieback symptoms include random dieback of twigs displaying tan foliage-photo credit Heather Kirk Ballard.jpg thumbnail

Boxwood dieback symptoms include random dieback of twigs displaying tan foliage. Photo by Heather Kirk-Ballard/LSU AgCenter

Yaupon holly can be trained as hedges in a formal gardens as a sutible replacement for litlleleaf boxwood-picture credit to Tammany Bumgarten.jpg thumbnail

Yaupon holly can be trained as a hedge in a formal garden as a suitable replacement for littleleaf boxwood. Photo by Tammany Baumgarten

Dwarf yaupon holly is a native alternative to littleleaf boxwood-photo credit to Tammany Bumgarten.jpg thumbnail

Dwarf yaupon holly is a native plant that can be used as an alternative to littleleaf boxwood. Photo by Tammany Baumgarten

10/11/2019 3:51:57 PM
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