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| Refresher Course on Fertilizing Trees |
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| Fertilizing typical and drought-tolerant trees in the landscape requires a knack for applying in the right season, using the proper approach and using the best product for the tree. Fertilizer is often misunderstood and misused. Fertilizer is not really direct food for trees, but instead, a boost to your trees providing the ingredients needed for photosynthesis and growth. Fertilizer should not only be used when minerals are lacking or absent in the soil but also to maintain a good chemical balance within the soil all year long. |
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| Drought-tolerant trees can be fertilized much in the same way as standard trees. These trees should be fertilized on a regular schedule, depending on the geography and status of the tree. Trees in areas that receive a lot of rain usually have a lot of natural nutrients in the soil and only require about one to two fertilizer applications a year. |
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| However, in more arid areas, like the Southwest, you should fertilize up to three times a year to produce more nutrients in the soil and to keep the plant healthy in each season. |
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| The best times for fertilizing are in early spring, mid-year and in the fall. The early spring is a good time because tree roots are coming out of the dormant period and require a boost to be healthy as they are starting to grow. Mid-year is also important because trees are experiencing more heat, absorbing water faster because of the heat and therefore going through nutrients quicker. To put in fertilizer during this time gives the tree a boost and replenishes those nutrients lost. 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 during the summer months. If water is unavailable, do not fertilize at all because plants will be unable to absorb the nutrients. |
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| A typical mistake most commonly made during fertilizing is overfertilizing, which can produce rank, weak growth that breaks easily and is susceptible to injury from cold, drought and pests. Using the wrong nutrient balance for the tree is also a mistake commonly made. |
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| Fertilizers are divided between the nutrients nitrogen, potassium and phosphorus. Nitrogen is for greening the tree, adding more foliage and nurturing the leaves. Potassium is applied to prevent diseases and helps with producing more, healthier flowering. Phosphorus boosts the root system and also helps with flowering. A Triple 15 fertilizer has 15 parts nitrogen, 15 parts potassium and 15 parts phosphorus. This combination of nutrients is perfect for trees, as you don’t want to use too much of one of these nutrients. |
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| When planning a new tree, put 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. For new trees, try using new fertilizer 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 this will waste fertilizer. Systemic liquid, spray-on fertilizer seeps into the tree leaves, limbs and bark and is absorbed into the root system. Just remember – the best practice is to use a balanced amount of nutrients. |
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| When fertilizing trees, keep these two points in mind: Fertilizer is beneficial when it is needed; but use it in the right amount, at the right time and in the right place, and don't hesitate to use an organic fertilizer. |
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| Source: Don Dobbs, Biggs Tree Co. |
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