Slow Release Fertilizer for Trees

Slow-release fertilizer can help a tree grow and thrive.

Just as water and proper pruning are important to helping trees grow and thrive, fertilizer can help provide minerals and nutrients that may be otherwise lacking in the soil. Slow-release fertilizers are a good choice for newly planted trees or in areas where quick-release fertilizer might quickly leach away from trees, thus depriving them of their effectiveness.

Types

There are two kinds of fertilizers available at most garden centers and home improvement retailers: quick-release and slow-release. Many horticulturists recommend slow-release fertilizers because they release the needed nutrients and minerals over an extended period of time. When choosing the product, look for numbers on the outside of the container to determine what kind of fertilizer you will use. Complete fertilizer mixes include: 10-10-10, 16-4-8, 12-6-6 and 12-4-8.

Function

A main component in fertilizer is nitrogen. In slow- or controlled-release fertilizer, some of the the nitrogen may be coated with a substance such as sulfur. Over time, water dissolves the coating and slowly releases the nutrients to help foster plant growth. It may be particularly helpful to use slow-release fertilizer on trees that are planted on slopes because the nutrients won't all wash away after watering or rainfall.

Considerations

In order to properly fertilize a tree, it should be spread over the root zone area, which generally surrounds the tree. To determine how far from the trunk of the tree to apply the fertilizer, measure the distance from the trunk to where the outermost branches hang. This is considered the dripline. Divide that number in half and add it to the number of the dripline. In other words, if the distance between the trunk and dripline is 5 feet, your fertilizer radius should be 7 1/2 feet around the trunk.

Time Frame

Trees that are planted in the fall should not necessarily be immediately fertilized. They need to first get over the shock of being planted and then settle in for the dormant period of winter. Once spring hits, the trees can receive a light sprinkling of fertilizer around the base of the tree. Spring-planted trees should be fertilized before growth starts. In most cases, new young trees need only a small amount of fertilizer--as little as 1 to 3 tbsp. Trees should not be fertilized during dry periods because the chemicals cause growth, which requires water.

Preferences

Although fertilizer spikes are convenient and easy to manage, they don't provide as much nutrition to all parts of the root system. Granules are preferred because all of the feeder roots have a chance to help bring needed minerals and nutrients into the tree.

References

• Clemson University Extension - Fertilizing Trees & Shrubs
• North Carolina State University - A Gardener's Guide to Fertilizing Trees and Shrubs