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Trees planted in lawns will benefit from the same fertilizers you apply to your lawn, so if you fertilized your lawn last spring or early fall, you may not need to fertilize trees planted in lawns.
These types of fertilizers are especially important if you're planting trees that don't quite fit your current soil composition or climate. They can also help soils that are severely nutrient-poor, promoting water retention and healthy root growth. [Sources: 0, 6]
The tree may already be getting enough nutrients from the soil, but it may benefit from additional fertilizers to help it grow at its best.
A tree of any age can already get acceptable nutrients from the soil - the quality of your soil depends on your region, among other things - but in general, all trees benefit from additional fertilizer. [Sources: 6, 18]
Several factors can affect a tree's need for fertilizer, including soil type, rainfall, and the overall health of the plants surrounding the tree. The appearance of the plants you are growing and the soil are the two main factors that determine whether your tree needs fertilizer. Fertilizers vary by tree type, soil properties, and climate. [Sources: 0, 4, 15]
The best fertilizer is one that delivers the nutrients your tree needs directly to its roots when it needs them. The purpose of fertilization is to place nutrients where they will be best absorbed by the roots of the tree. [Sources: 1, 3]
This allows the fertilizer to reach the nutrient-absorbing main roots of the tree, which are usually several inches high in the soil. With the deep introduction of fertilizers, nutrients sink into the soil to a depth where the roots of trees and shrubs grow.
This fertilization process involves injecting nutrients (and other substances if necessary) directly into the soil, rather than spraying it from above. A common root dressing method for home gardeners is to buy tree fertilizing tips and press them into the soil. [Sources: 1, 4, 6, 7]
Since most of the tree's roots are at the top of the soil, spread the fertilizer evenly with a rotary or drip spreader over the root zone area to fertilize the tree.
Place the fertilizer in holes 6 to 12 inches deep about 2 feet apart in concentric circles around the trunk of the tree and extend them about 6 feet beyond the scattered branches of the tree. Apply fertilizer along the drip line of the tree, in areas with most of the roots.
Another way to apply fertilizer is to "sprinkle" the soil with fertilizer as you walk around the tree drip. [Sources: 2, 11, 12]
A high-pressure feed rod penetrates the shallow roots and injects the fertilizer solution several inches below the ground, where there is less competition and nutrients are more readily available to the tree. A tree's root system can extend a great distance over time, continuing to absorb nutrients as the surrounding area is fertilized.
Trees' root systems extend long distances, absorbing nutrients while fertilizing the surrounding area. During this time, tree roots absorb nutrients from the soil and use them for important health-promoting functions, such as root development and disease resistance, rather than just producing new shoots. [Sources: 2, 3, 5, 7]
When you plant new or young trees, they actually absorb nitrogen from fertilizers, which helps them grow quickly and develop a dense canopy well into fall. Young trees that haven't been planted recently, especially those with trunks less than six inches in diameter, can benefit from regular fertilization.
Newly planted trees may need additional fertilizer to increase their winter energy reserves. [Sources: 4, 5, 18]
Never fertilize in late summer or early fall, as available nutrients stimulate new growth when trees and shrubs are ready to go dormant. Trees and shrubs that should not be fertilized include newly planted specimens and trees with severe root damage from recent trenching or construction.
Even trees with damaged roots during excavation or construction should not be fertilized. [Sources: 8, 10, 15]
Trees and shrubs in the landscape may require little or no additional fertilizer if plants are positioned correctly, fallen leaves are ground in place, and fertilized with nutrient-rich mulch or surrounding grass.
However, it may be necessary to fertilize trees and shrubs growing in flower beds, especially in sandy soils with little or no organic matter. Trees and shrubs should be fertilized in early spring, with a small amount in early summer if conditions are favorable for plant growth (i.e., acceptable temperature and soil moisture).
Fertilize plants, shrubs, trees, and lawns to encourage root growth, which will help plants survive winter and recover faster in spring. [Sources: 9, 11, 12]
Spring feedings help ensure your trees have enough nutrients to maximize leaf and flower growth. During the growing season, fertilizer can help the tree overcome mineral deficiencies and fight infections.
If you see these signs, fertilizing can be part of a holistic approach to restoring the health of your plants. When you fertilize your trees, you are replenishing essential minerals and nutrients missing from the soil. [Sources: 1, 3, 17]
Fertilizers applied to the lawn around the tree usually provide most of the minerals needed to keep the tree healthy. In many cases, fertilizing lawns can provide enough nutrients to meet the needs of the trees in the area. Unfortunately, our soils don't always contain enough nutrients to meet these needs.
Soil conditions in residential and commercial areas are often insufficient to support healthy tree growth. Since trees need nutrients to survive and grow, soils lacking one or more of the nutrients that trees need to reach their full potential will be more susceptible to disease, insect problems, and have a shorter lifespan than similar trees that grow well Fertilization. [Sources: 4, 5, 11]
As a result, trees usually respond better to fertilizers with a 2-1-1 or 3-1-1 (Nitrogen-Phosphorus-Potassium) ratio. The tree needs more nitrogen (N) fertilizer during the growing season. [Sources: 11, 16]
Look for slow-release (also known as controlled) tree fertilizers with a low salt index. Your new tree may need a little extra fertilizer until it stops growing more leaves and roots. This can encourage leaf expansion at the expense of root growth, making new trees vulnerable to drought stress.
Fertilization may be required to compensate for nutrients "extracted" from the root zone by removing leaves. [Sources: 1, 11, 17]
Trees that grow in closed pots or building mounds usually require frequent fertilization. Trees are often neglected in the spring when it comes time to fertilize the yard. Around foundation plantings, a lower rate of nitrogen fertilizer is used to reduce overgrowth and the resulting need for pruning and pruning. [Sources: 10, 14, 18]
Sources
[0]: https://www.rwhendricksenco.com/homeowners-guide-how-and-when-to-fertilize-trees/
[1]: https://www.independenttree.com/tree-shrub-fertilization/
[2]: https://extension.oregonstate.edu/news/spring-good-time-fertilize-young-trees-shrubs
[3]: https://www.treehelp.com/how-to-fertilize-a-tree/
[4]: https://alpinetreenj.com/do-trees-need-to-be-fertilized/
[5]: https://evergreenlandscapes.ca/blog/the-guide-to-fertilizing-trees/
[6]: https://pss.uvm.edu/ppp/articles/treefeed.html
[7]: https://texastreesurgeons.com/blog/2019/03/29/do-my-trees-really-need-fertilizer/
[8]: https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/fertilizing/
[9]: https://www.directnativeplants.com/the-best-time-to-fertilize-your-plants-shrubs-trees-and-grasses/
[10]: https://extension.umd.edu/resource/fertilizing-trees-and-shrubs
[11]: https://extension.missouri.edu/publications/g6865
[12]: https://hgic.clemson.edu/factsheet/fertilizing-trees-shrubs/
[13]: https://www.growingagreenerworld.com/fall-fertilization-for-established-trees-and-shrubs/
[14]: https://canopy.org/blog/do-trees-need-fertilizer/
[15]: https://treesunlimitednj.com/when-and-how-to-fertilize-trees/
[16]: https://www.thoughtco.com/basics-on-tree-fertilization-1343346
[17]: https://blog.davey.com/2016/05/what-when-and-why-the-best-way-to-fertilize-trees/
[18]: https://treedoctorkc.com/do-you-need-to-fertilize-your-trees/
