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Flowers, Fruits, and Frass

The Brass Tacks of Boxwoods in Your Illinois Landscape

Boxwoods want intermediate sun or shade. In full shade, they may not be as vigorous and have a looser shape. In full sun, they may scorch in our hot summers or bronze in the wintertime.

Do not prune until after the chance of frost has past unless you are trying to control previous year's pest issues.

Boxwood have shallow roots, so instead of planting ground covers or annuals around them, mulch.

Boxwoods will not do well if planted in soggy soil, or exposed to dry winter winds.

Boxwoods host three pests, all of which can be controlled with spring time treatments:

  • Boxwood psyllid are tiny insects that feed on plant sap, causing the leaves to curl and become sticky, but are not a threat to plant health or vigor. Monitor for them in the spring as the overwintering eggs begin to hatch.
    • Most of the population can be controlled by either removing new growth or with an insecticidal soap spray. Good coverage is necessary and may be difficult as the nymphs hide out in the cupped foliage.
  • Boxwood mites appear as squiggly whitish lines on the evergreen leaves. These mites steal the chlorophyll from the plant making it unsightly and unhealthy. They are most active in spring and early summer.
    • Use an insecticidal soap, providing coverage on both sides of the leaves and plan on a second spray seven days later so you can get the next generation.
    • Cleaning up debris and spray water on plant to increase humidity and knock off mites.
    • Ordering beneficial predatory mites off the internet and release them when the population is lower. Sprinkle water on the foliage first and then evenly distribute the mites over the plants. These can be extremely effective in reducing the population, and are easy to acquire and use. Limit your pesticide use and label yourself the Innovative Gardener on the Block.
  • Boxwood leaf miners lay their eggs in the new growth of the boxwood. Eggs hatch in three weeks and begin to feed, mottling the leaves with whitish-yellow marks that may be un-noticeable at first, and slowly forming a blister on the leaves. By mid-summer, the entire leaf will have several yellow blister-like marks. Severe infestation causes leaf drop and branch dieback. Boxwood leaf miners then overwinter as larva within the blister. As temperatures warm, the larvae becomes active and soon form an orange pupae that may stick partially out of the blister in the leaf.
    • If adult midges (flies) are seen around your boxwoods, prune out new growth to get rid of eggs.
    • Spray foliage with Spinosad twice, about three weeks apart. The first spray will occur when the weigelas are blooming. Even though Spinosad has proven a low-risk to bees, spray later in the day to allow the foliage to dry before sunset, so morning feeding isn't disrupted.