Common Problems With Rosemary Plants

Bugs

• Rosemary resists most insects. Its woody stems and plant oils are natural barriers to many insect incursions. The shrubs may be seasonally infested with aphids, whiteflies, spittlebugs and other small insects. These insects usually cause little damage. Blast them off with a stream of water. If aphids or whitefly infestations are heavy, insecticidal soap may be used. Spittlebugs, detected by their foamlike discharge, live on weeds or plants near the rosemary. They are harmless but unsightly. The most effective spittlebug control is removing the nearby host plants.

Disease

• Rosemary grows as a dense shrub, hedge or spreading ground cover. Under humid conditions, fungal diseases such as powdery mildew affect the foliage. Minimize infection by planting rosemary in full sun, thinning foliage to allow air circulation and watering in morning so that foliage dries quickly. You can apply fungicides such as horticultural oils. Other fungal problems such as root rot and crown rot occur when soil drains poorly or is wet for long periods. If the rosemary is in a container, ensure the container drains well. When rosemary is in the ground, improve drainage by working organic compost into the soil. Rosemary roots need to dry between waterings.

Exposure

• Rosemary needs sunshine. Without enough sun, leaves turn yellow and fall from the branches. Remove any overhanging plants that shade rosemary. Transplant the rosemary if necessary so that the plant receives at least six hours sunlight daily. Rosemary does not tolerate extreme cold. Frost can damage and dehydrate the plant, resulting in brown, brittle leaves. Trailing rosemary used as ground cover tolerates cold more easily than upright bushes. Wrap upright rosemary in plastic or other weather barrier fabric during freezing temperatures.

Considerations

• When rosemary branches are damaged, they are more vulnerable to insect and disease problems. Trim off and discard these branches. Periodically check the interior of the plant. If inside leaves are dead and branches are weak or dead, prune out enough branches to let light and air into the plant. Avoid pruning when rosemary is in bloom as it may be covered with pollen-gathering bees. Rosemary should be planted away from doorways . This minimizes exposure to bees. Mice often nest under dense shrubs like rosemary. Be aware that snakes may be seeking rodents near rosemary plants.