I have a large Walnut tree in my yard, how should I take care of it? Fred from Paso Robles.
Jutta Thoerner UCCE Master Gardener
The California climate is ideal for growing walnut trees. In 1867, Joseph Sexton planted the 1st known walnut orchard in California. Today’s acreage exceeds 222, 400,000. Demand has outperformed production since the health benefit of the walnut has been discovered. Originally, walnut trees have been dry farmed in CA; its long tap root is an ideal tool for summer survival. The walnut tree does not like “wet feet”. Over- irrigation often causes oak root fungus and a wet trunk promotes gall diseases. If you have a good loamy soil, no additional water is needed if you keep the root zone under its canopy weed free.
Here are some tips to Identify your tree: A black walnut is identified by its deep furrowed bark. Leaves have 15-23 leaflets. The English walnut tree has a smooth bark and has leaves with 5-7 leaflets. Combinations of a black walnut trunk and rootstock with an English grafted on top are common in Paso Robles. If you have a Black walnut tree, you need to consider that it hinders the growth of other plants by root competition and by secreting a growth inhibiting substance.
Regarding insect pests, the walnut husk fly is a small fly that deposits its eggs inside the nut by piercing the green husk. The emerging larvae feed on the nut and will ruin the nut meat. A good option for monitoring and catching the fly are yellow sticky traps, which, by the addition of an added pheromone, attract the female fly. Putting these traps out by June and monitoring them weekly will help avoid serious infestations. Other less common insect pests are scales, spider mites, aphids and codling moth. Ask your local Master Gardener office to help you identify these insects. And unless you like to share your harvest with rodents, consider trapping ground squirrels and tree squirrels. Apparently they also know about the health benefits of the Walnut; a tree squirrel can squirrel away 104 lbs. of nuts a year!