It can be easy to forget that our trees need regular fertilizing – even well established trees. Why is that? The soil in the arid desert can be nutrient defficient and the lack of essential nutrients can lead to a shorter life span, limited growth, or poor leaf production. But just throwing down any fertilizer isn’t helpful. Here are the factors to consider when fertilizing your trees:
It’s no secret that desert soil is not naturally very fertile – especially for non native plants. In general, Arizona low deserts are very alkaline, typically high in calcium. The best way to counteract this is by adding more acidic compounds to balance the PH of the soil. This includes sphagnum peat, elemental sulfur, aluminum sulfate, iron sulfate, acidifying nitrogen, and organic mulches.
In addition to soil composition, the variety of tree that is being fertilized is important to consider as well. While many non native trees thrive in the desert, they may need different or additional feeding than their native counterparts. Conversely, native trees may need a simple fertilizer – meaning just one element such as nitrogen. Verses non native trees benefit from complete, or multiple elements like iron, phosphorus, and nitrogen as well.
Timing & Temperature
While regular is essential to the long term health of your tree, when it’s fertilized is just as important. Space out feedings to prevent over feeding your trees. A good rule of thumb for many citrus trees is to fertilize on 3 holidays: Valentine’s Day, Memorial Day, and Labor Day. These are the peak times for fruit production for the trees and when nutrients are needed most. Most other trees can be fertilized anytime between fall and spring, with an emphasis on spring before the heat of the summer.
High temperatures are stressful for trees and applying fertilizer can actually have a negative impact. If the temperature is over 105 degrees consistently, do not fertilize. The acidic make up of the fertilizer coupled with the hot temperatures can spell disaster. During the hot summer months, care for your trees with deep and more frequent watering rather than feeding with fertilizer.
Once you know what type of fertilizer to use, how you apply it is just as important. The application depends on:
- type of tree
- size of tree
- location; i.e. surrounded by rocks, grass, etc.
Typically, fertilizer should be placed just inside of the drip line (the outter most leaves of the tree) towards the trunk. Fertilizer must be able to penetrate down to the feeder roots which are 6-12 inches down from the surface. Ensure that the fertilizer meets it’s mark by drilling holes into the ground at those distances. If using liquid fertilizer, use the same hole method or water deeply and check watering depth. Sprayable iron is also an option to apply directly to the leaves of the tree.
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