Question: I have fruit trees and need to fertilize them. What kind and how much fertilizer should I apply?

Answer: Of the three macro nutrients-nitrogen, phosphorous, and potassium, required by law to be stated on fertilizer packaging, only nitrogen is needed for established fruit trees growing in Cochise County. As the season progresses minor nutrients such as iron and zinc may need to be applied. The amount needed for proper growth is determined by measuring the inches of trunk diameter six inches from the ground. This figure is multiplied by 0.1 pounds of actual nitrogen for apples and pears. For peach, cherry, other stone fruits, and grapes multiply trunk diameter by 0.05 for actual nitrogen requirement. For example: An apple tree has a 4-inch trunk diameter, so it needs 0.4 pounds of actual nitrogen. Ammonium sulfate (21-0-0) contains 21% actual nitrogen or 21 pounds of nitrogen in 100 pounds of fertilizer. Dividing 0.4 by 21% equals 1.9, or just under 2.0 pounds of 21-0-0 fertilizer for the tree in question. I recommend a split application. Apply half the amount now and then the other half six weeks later because our sandy soils do not hold water and nutrients very well, and they leach through the soil profile out of the root zone. Distribute the fertilizer around the tree drip-line and water in. The same calculations would be made for "organic" fertilizers. Remember that manures usually have only one or two percent nitrogen. For example: using steer manure, a four-inch diameter tree requires 0.4 pounds of nitrogen. Divide 0.4 by 1% equals 40 pounds of steer manure per tree.

For further information refer to: Backyard Fruit Production in Southeastern Arizona, Cooperative Extension Publication #9015.

Question: I want get lid of weed seed and other pests in my garden soil. I have heard of soil sterilization using plastic. How can I do this and is it effective?

Answer: This technique, soil solarization, utilizes heat, moisture, and time to reduce certain weeds, fungal diseases, nematodes, and other detrimental soil organisms. A clear polyethylene plastic sheet, several mils thick, is placed over moist, well tilled soil. Dig a shallow trench around the treatment area and place the plastic sheet edges down with soil from the trench. During the summer months with high temperatures and solar radiation, heat is generated and retained under the plastic. Over time the heat penetrates deeper into the soil profile and temperatures exceed the thermal death point for many organisms. Ideally, plastic should remain in place for six to eight weeks. Water condensing on the plastic sheet is normal. Soil solarization is not soil sterilization, but rather pasteurization. Some tough weed seeds like field bindweed, also called morning glory, will normally not be controlled unless this treatment remains in place for three months. This treatment should be in place during the last of May, June or July because these are the hottest months of the year.