Fertilizing Your Landscape Trees
Fertilizer is often misunderstood and misused. It is not really direct food for trees, but instead a boost providing the ingredients needed for photosynthesis and growth. A frequent misconception is that fertilizer should be applied only when minerals are lacking or absent in the soil. However, it also can maintain a good chemical balance within the soil all year long. Here are some tree fertilizer tips.
Fertilizer is beneficial when it is used in the right amount, at the right time and in the right place. The two most common mistakes made during fertilization are over-fertilizing and using the wrong chemical balance.
Trees should be fertilized on a regular schedule, depending on geography and status of the tree. Trees in areas that receive a lot of rain usually have plenty of natural nutrients in the soil and only require about one to two times a year of fertilizer application. In more arid areas, fertilizer should be used up to three times a year to produce more nutrients in the soil and keep the plant healthy.
The best times for fertilizing are in early spring, midyear and fall. The early spring is a good time because tree roots are coming out of a dormant period and require a boost to be healthy as they push out new growth. Midyear is important because trees experience more heat and therefore absorb water and go through nutrients faster. During the fall, tree roots have cooled a bit, but there isn’t as much rainfall as during winter months.
Avoid fertilizing trees and shrubs stressed by drought. If water is unavailable, do not fertilize at all, because plants will be unable to absorb the nutrients.
Excessive fertilizer results in rapid but weak growth that breaks easily and is susceptible to injury from cold, drought and pests. Also, the surplus fertilizer not absorbed by the plant roots may contaminate water. Use the amount specified on the bag.
The first number on a fertilizer bag label is the percentage of nitrogen. Nitrogen is for greening the tree, adding more foliage and nurturing the leaves. The second number is the percentage of phosphorous, a chemical that boosts the root system and amount of flowering. The third number on the package is the percentage of potassium, which helps prevent diseases and produces more abundant and healthier blooms. The best practice is to use a balanced amount of chemicals.
A triple 15 fertilizer has 15 parts nitrogen, 15 parts potassium and 15 parts phosphorus — a perfect combination for trees, as you don’t want to use too much of any one of these chemicals. Too much nitrogen and the tree may burn. Excessive potassium may cause calcium and magnesium deficiencies. Too much phosphorus could interfere with the availability of copper and zinc.
In addition to liquid and granular forms, fertilizer also is available as tablets. Liquid fertilizers are fast acting. Systemic liquid, spray-on fertilizers seep into the tree leaves, limbs and bark and are absorbed into the root system. Granular fertilizers are applied dry and must be watered in. When planting a new tree, place granular fertilizer in the ground just under the root ball. For trees already planted or established, spread fertilizer on top of the plant and water generously so the fertilizer seeps into the soil. Since most of a tree’s roots can be found in the top foot of soil, broadcast the fertilizer evenly with a rotary or drop-type spreader over the root zone area to fertilize the tree. For new trees, try using tabs that slowly release fertilizer and penetrate into the tree over a period of time. These tabs should be used in the ground planted near the root ball and never used on top of the soil, as that will waste fertilizer.
Donnie Dabbs, General Manager
Briggs Tree Company, Inc.
1111 Poinsettia Ave.
Vista, CA 92081