Spring tree fertilization is common as most trees have their greatest need for nutrients in the spring. In Portland this spring application usually happens in March or April as, rainy, cold weather wanes and sunny weather begins to show its face.
Trees in the city need fertilization because many of the natural processes that take place to add nutrients to the soil are disrupted. 
Leaves and other debris are cleaned up before they can be reincorporated into the soil. Soil is often compacted so many nutrients are washed away as urban runoff. Also, the presence of pollutants can strip nutrients from the soil or disrupt their absorption.
If your tree is having health issues, fertilization is likely an important part of getting that tree back into tip top shape, but you need to be sure that the problem that caused the tree to be unhealthy has been resolved. A Certified Arborist can help you identify and diagnose health issues. Trees are similar to humans in that when we are sick good nutrition can go a long way to getting us back on our feet, but in some cases additional medicine or other interventions are required to achieve and maintain our health.
In our practice, we utilize 2 basic types of fertilizers:
- Chemical: This is your basic man-made chemical fertilizer. There are several reputable brands which have developed formulations made specifically for either Deciduous or Evergreen trees, and for application in either the spring or the fall. Two of the most popular brands are Jobes and Phc for trees. Jobes is a good quality one that has an organic option and is available at most Home Depot stores. Phc is a little harder to find but has excellent proven results and is what many professional arborists use.
- Natural Mix: For us this is a compost tea mixed with Mycorrhizal Fungi. This fertilizer combination is a more organic option that mimics nature. The Mycorrhizal Fungi helps with the absorption of the nutrients and, we have seen great results with their use of urban trees. This application is somewhat custom and cannot be bought off of the shelf.
Fertilization options for trees also come is several application options. Fertilizer in most cases can’t be just spread on the ground surrounding the tree. It needs to be inserted under the soil 6”-12” down into the root zone of the tree. Those application options are:
- Tree Spikes: These are the most common option for a DIY fertilizer application. Tree spikes are soil form fertilizer which is formed in a spike shape which can be driven into the ground by hand (of at least in theory they can).
- Deep Root Fertilization: This is a liquid fertilizer pumped into the soil using a long wand attached to a commercial pump. This method is favored by professional arborists.
- Injections: Fertilizer applications can be injected directly into the tree, but this is usually only done in extreme cases or when the tree is also receiving another type of injection.
When is come to fertilizing your tree there are many options for both the do-it-yourselfers and the folks in need of a little more professionals intervention. If you do fertilize your tree yourself be sure to read and follow the manufactures instructions. This is only a primer on the vast topic of trees and fertilization so achieving success in your project will likely require some additional research.Feeling a little overwhelmed don’t worry our certified arborist would be happy to help.
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