Redbuds are trees of the genus Cercis. Popular species include the eastern redbud (Cercis canadensis, hardy in U.S. Department of Agriculture plant hardiness zones 4 to 9), the western redbud (Cercis occidentalis, USDA zones 7 to 9), the Texas redbud (Cercis canadensis var. texensis, USDA zones 5 to 9) and the Chinese redbud (Cercis chinensis, USDA zones 6 to 9). Growing 15 to 30 feet tall depending on species, redbuds have pink or white flowers early in the spring. Though prone to a number of insect, disease and environmental stresses, proper care will extend the life of redbuds.
Keeping the Soil Moist
Redbuds prefer moist, well-drained soils. They do not grow well in permanently wet soils. Watering redbuds especially through periods of extended drought will help them stay healthy. Water near the drip line of the tree and not at the trunk; the drip line is the area under the outer circumference of the tree canopy where water drips down to the ground. Running a soaker hose or sprinkler over this area for about two hours will ensure that the water penetrates deeper into the root zone. Check to see if the soil is moist by digging a small, 2-inch deep hole with a garden trowel and feeling with your finger. If the soil feels moist, you do not need to water the tree.
Mulch is needed to help keep the area around the tree moist and to reduce weeds. After removing weeds, add about 3 inches of mulch around the tree extending to the drip line. Keep the mulch about 4 inches away from the tree trunk to prevent rot.
Have your soil tested before fertilizing redbuds to determine which nutrient formulations may be beneficial. Many local county extension offices provide test services. Redbuds tolerate a wide variety of soil conditions from slightly acidic to slightly alkaline soils, so fertilization may not be necessary.
Nitrogen (N) fertilizers applied once per year in the early spring may help tree growth. A safe level of nitrogen to apply without over-fertilizing is 0.1 pound per 100 square feet. For a basic 10-10-10 fertilizer formulation, this equates to 1 pound of fertilizer for every 100 square feet. Dry or granular fertilizers can be applied by hand or with the use of a mechanical spreader to the soil under the canopy; water thoroughly after application.
Redbuds are natural understory trees and you do not necessarily have to prune them, but pruning can help improve their health and appearance. Prune out dead branches, weak V-shaped crotches and crossing limbs in the spring after flowering. Remove lower limbs to raise the tree from the ground and improve light penetration. Remove suckers --stems coming up from the ground -- to give the tree a single-stem appearance and improve structure.
Since redbuds are smaller trees, lopping shears can be used to prune out medium-sized branches. For higher branches, a pole saw works best. To prevent disease spread, disinfect pruning tools between cuts by wiping with a cloth soaked in isopropyl alcohol.
Redbuds are susceptible to cankers caused by a variety of fungi. Cankers appear as sunken areas of bark surrounded by raised callus tissue. Prune out branches with cankers when they are detected to prevent disease spread, disinfecting tools between cuts. Prune during dry weather and make cuts 6 to 8 inches below the edge of the canker.
Verticillium wilt is a fungal disease of redbuds that infects trees through the root system. Symptoms include leaf wilting, yellowing and branch dieback. To prevent the disease from spreading, prune off infected limbs and do not let infected leaves remain on the ground. Rake up and remove infected leaves and branches and discard them, but don't place them in your compost pile.
There are no effective fungicides for treating cankers or Verticillium wilt on redbuds.
Many insects can attack redbuds, but damage is not usually severe. Two of the most concerning insects pests on redbuds are scales and leaf-feeding caterpillars.
Scale insects are sap-feeding insects that insert their tiny, strawlike mouthparts into the bark of trees. Once mature, scales settle in at a feeding spot and form a protective waxy coating which makes them difficult to control. The best time to control scale insects is shortly after they hatch while they are in the nymph or "crawler" stage. Spray the tree with a ready-to-use horticultural oil spray as soon as the scale crawlers become active in late winter or early spring. Releasing natural predators such as lacewings or ladybugs will help control scale and whiteflies, another pest of redbuds.
Caterpillars can be controlled by pruning off branches with eggs or tent caterpillar nests. Caterpillars can also be picked off by hand and crushed or dropped in a jar of soapy water. When purchasing insecticide sprays, read the label carefully and make sure that the specific caterpillar is listed as one of the insects it can control. Products that use a bacterium, such as Bt, are considered less toxic to the environment than the traditional contact poisons. Bt var Kutaski is the active ingredient for caterpillar control. It is often sold as a liquid concentrate and requires mixing; the label will specify the number of teaspoons to mix into a gallon of water for spraying.
Whenever mixing and applying any type of insect control product, wear gloves and a long-sleeved shirt to avoid direct contact with the solution.