Lemon Tree with "Issues"

Q. I have a lemon tree with some possible “issues”. It has been in the ground 10 years, about 8 feet tall, but recently the leaves are turning yellow to brown and the branches are losing leaves in some spots. There is about 3-4" of rock under tree and thick weedblock under the rock.

In our Mojave Desert soils sometimes using rorck mulch on the soil surface can create problems.

A. If you read my column regularly, you may know what I’m about to say. In our desert soils, placing rock on the soil surface beneath fruit trees is a no-no. You might get away with it in other deserts where there has been some form of agriculture, but not here. Frankly, I’m surprised it has taken 10 years for the leaves to begin yellowing and browning. That may be a new record!

            Soils are made up of two major components; the mineral component which is sand, silt and clay and organic component. Our desert soils are extremely low in the organics; the “good stuff” that make soils come alive. We refer to this component as the organic component or “organics” or “organic matter” of the soil.

            Organics in the soil should rot or break down over a few years and disappear if not replaced regularly; every year in vegetable and herb beds or at least every 2 to 3 years around trees, fruit trees and shrubs. Trees and shrubs that originate in deserts, i.e., desert adapted, can tolerate soils with little organics in them. But that’s not true of plants that don’t come from deserts. This includes citrus.

            Your lemon tree is “behind the curve” regarding organics in the soil. The soil is probably extremely depleted. Adding compost or other sources of organics to the soil surface may not make much difference for a couple of years.

            I would remove the rock, punch holes in the soil, pour compost in these holes so that compost can impact the roots quickly. Or lightly mix compost into the upper surface of the soil. Compost tea may help. Add a cup of compost to a 5-gallon bucket of water, stir it, let it seep for a couple of hours and pour it over the top of the rocks. But ultimately you must get organics into the soil near the tree roots.

            Check the irrigation and make sure the tree is getting enough water. An 8-foot citrus tree should get about 20 – 30 gallons of water each time it’s irrigated. The water should be applied to at least half the area under the tree. Next February, add iron chelate to the soil to correct andy possible leaf yellowing due to iron chlorosis.