Time to Feed Trees and Shrubs
by Jim Cameron - October 2006
Jim Cameron is a certified arborist for Ryan Lawn & Tree. He can be reached at (913) 381-1505.Nature provides windows or “best times” for our garden activities. Fall, when most trees drop their leaves, reminds us it is time for homeowners and arborists to feed trees and shrubs.
Why do we supplement the feeding of our trees when it isn’t done in the woods? There are several reasons. We really don’t have natural environments in the city. We mix trees and lawns together. You don’t see manicured grass in the woods. Maybe more importantly, nature really doesn’t care if a tree dies or not. Nature is not really in balance. Usually something will quickly fill a void, be it poison ivy, a thorny briar, or a tree; nature really doesn’t care. Homeowners do care. This is why we work to provide a favorable growing climate for your trees and shrubs.
Let’s look closer at the feeding of trees and shrubs. The most lacking plant nutrient in the soil is nitrogen. It is naturally occurring, but most of it is in the air. For plants to use nitrogen, it must be in a soluble form in the soil.
In our landscape, there is a constant struggle for nitrogen between our lawns and the trees and shrubs. Turfgrass’ root system is much denser and retrieves most of the available nitrogen.
Often people mention they regularly fertilize their lawns and assume that the trees and shrubs benefit from this as well. However, the turfgrasses’ massive root system leaves little nitrogen for other plants.
Fertilizing your trees and shrubs can help. A slow-release, nitrogen-based fertilizer is the best. You can get fertilizer in different forms such as liquid, granular or organic.
How do you apply tree and shrub fertilizer? For a homeowner, the compressed fertilizer stakes work well on smaller trees. An iron post shoved into moist ground and then removed provides a depression where you can pour granular fertilizer. A spouted pitcher will help you direct round fertilizer prills into the hole without spilling any into the lawn. This is important because concentrated fertilizer can quickly burn a hole in your grass.
Commercially, the most common method is to inject a liquid fertilizer into the soil. This is the easiest method to provide enough plant food to make a difference for a large tree.
When applying, it is important to place the fertilizer below the grass roots. To do this, we recommend you apply the fertilizer 3-6” below the soil surface. Getting the fertilizer below the soil surface will help it absorb into the lower portion of the soil where tree roots have a better chance at getting their share.
Where do you actually put the plant food? If you start at the edge of the drip line and work in toward the trunk, you will place the food where the tree has actively growing roots. Again, I will reference what we do commercially, because we get good results. We space the fertilizer injection sites every 24-30” apart. We usually work from the drip line to within a few feet of the trunk. On small trees, we inject within a foot of the trunk.
When is the best time of year? Fall fertilizing mimics nature and gives excellent results. We normally recommend you feed new or younger trees and shrubs. Also, consider feeding any environmentally stressed tree or trees you want to grow at an increased rate. A key factor in fertilizing woody plants is to use a slow release fertilizer.