Fertilizing your Trees and Shrubs
In the spring, trees and shrubs break their winter dormancy and begin growing taller and producing new branches. In the nursery business we call this a “flush” of growth. To do this they rely on nutrients stored in their roots from last year’s growing season. Most homeowners experience a single flush of growth in their landscape plants during a single growing season. In truth, many species of trees could grow much more if they had proper fertilization. Many species of trees, especially oaks, will flush growth multiple times during the growing season. Each flush can add one to two feet or more to the overall height of the tree. Some species of oaks can grow at least 5 feet in a year due to these multiple flushes. Red, Bur, Pin, Chinkapin and Shumard Oaks are some of the fastest-growing of all the tree species we sell. Black oaks and white oaks are admittedly slower-growing oaks, but they can still be relied upon to add a couple of feet per year. In the nursery we expect the fast growing oaks to flush new growth monthly. This can only happen if they are given proper fertilization. This care sheet is designed to help you push your trees to get the best possible growth.
Fertilizer applied in a timely manner will help trees accumulate nutrients needed for summer flushes, and these nutrients will also be stored in the roots for the first flush of growth in the next growing season. A water soluble liquid fertilizer (LF) like Miracle-Gro or Peter’s with micronutrients or a controlled release fertilizer (CRF) like Osmocote or Nutricote with micronutrients can be used with good results. Each of these products is available at your local garden center. We use LF fertilizers throughout the growing season in the nursery. We have used CRF’s with fine results although we did supplement with LF later in the growing season. This combination of both liquid feed and controlled release fertilizer has yielded good results. The benefit of a controlled release fertilizer is that, as the name implies, the fertilizer is released over an extended period of time. These tend to release most of their fertilizer early after application leaving relatively little for later in the season. Thus some growers supplement with LF late in the season.
Starting this year, your fertilizing regimen has two purposes: to push growth during the current growing season and to get nutrition into the roots where it will be stored for growth next spring. In central Ohio, begin applying fertilizer about the first week of May. If the winter has been harsh, you may hold off application until the middle of May or when buds actually break out into young branches. See Table 1. Time your fertilization to when the first few inches of new growth develop in the spring. This early fertilization probably has only limited direct benefit to the first flush of growth because most of the growth seen during this spring flush is driven by the previous year’s nutrition stored in the roots. However, fertilizing now will charge the soil with nutrition that is available when the tree requires it.
Fertilization Schedule for Home Landscape Trees.
Based on a Central Ohio growing season that starts in early May and ends in late August.
Fertilization should stop in late August or the first week of September. This allows approximately 6 weeks for the new growth to harden off before the first winter freeze.
Follow the label instructions on whatever form of fertilizer you use. CRF can be top-dressed (spread directly on the ground around the base of the plant a few inches from the trunk) or buried slightly in the soil around the base of the plant. If the tree is small, keep the fertilizer closer to the trunk but not in contact with the trunk. If the tree is larger, apply it further from the trunk, but always keeping it within the dripline of the tree. Do not apply CRF in a single pile as this might cause burning of the plant. Distribute it evenly around the tree away from contact with the trunk.
The schedule in Table 1 has resulted in great growth for the trees in our home landscape. Our soil is very well drained so we literally apply fertilizer at will. If your soil is not particularly well drained, you may want to decrease the LF interval to once every 3 weeks or more. In wetter, heavier soils another alternative is to apply a CRF which offers the nutrition your trees and shrubs require without the water they do not need.
Below is a simple method to make an inexpensive watering/fertilizing tool for applying LF. It is a good alternative to the expensive watering bags sold at garden centers.
- 5 gallon bucket (as many as you think you will need)
- 1/16 or 3/32 drill bit and drill
- water soluble fertilizer (LF)
Turn the bucket over (bottom side up) and drill a single hole in the side of the bucket ½” above the floor of the bucket.
Fill the bucket with water and mix in the amount of fertilizer as indicated on the label. At this point, some fertilizer water will be leaking out, but not much.
Now place this leaking bucket about 6” from the trunk of your tree with the stream pointed towards the trunk and let it slowly soak the ground around the tree.