Proper fertilization of tree and small fruits is essential for the production of quality fruits, but not all fruits are fertilized the same way. Before making any applications, the first priority of a smart gardener is to test the soil to determine the nutrient needs of the crops. Michigan State University Extension offers a soil test kit that can be purchased online at the MSU Extension Bookstore. After receiving the kit, follow the directions for collecting the sample and mailing for analysis.

When the results have been returned, go to MSUSoilTest.com and select the “Understand Your Soil Test Results” bar for further instructions and recommendations for timing of applications. Fruit trees should be fertilized in the early spring before growth starts if there are indications such as low annual growth; damage from weather extremes; light green leaves; or a soil test indicating a need for nutrients before planting. Mid- to late April is an ideal time.

Once the amount to be applied has been calculated, it should be placed in a wide band under the farthest branches from the trunk, or the drip line, of the tree. Most of the roots that pick up water and nutrients are in this area. Instead of broadcasting, some people prefer to drill holes around the drip line using an auger for the fertilizer placement. This method is acceptable, but more time consuming if there are many trees to fertilize. In the absence of a soil test, a general recommendation would be to apply 1 cup of 12-12-12 per inch of tree trunk diameter. The maximum application for a mature tree is 8 cups.

Strawberries should not be fertilized with the full recommended rate of nitrogen in early spring. Applications at that time will result in soft berries. The best time to fertilize strawberry plants is following harvest at a rate of 2 to 3 pounds of 12-12-12 per 100-foot row. If a soil test indicates a need for phosphorus or potassium, these nutrients may be applied in the spring without causing berry softening. Sometimes small amounts of nitrogen fertilizer may be beneficial for strawberries in the spring. If the plants are not growing vigorously, are light green, or the plants are growing on sandy soils and there has been higher than normal rainfall, an application of nitrogen at a rate of about 0.5 pounds per 100-foot row should be OK.

Blueberries, grapes, raspberries and blackberries are fertilized in the spring before growth starts as well.

The fertilizer requirements for blueberries are different from the other fruits. They grow better when ammonium sulfate is used for nitrogen and potassium sulfate as a source of potassium. They do not do as well when a nitrate form of nitrogen or potassium chloride is used. The label on the fertilizer bag will list the nutrients and what forms are used.

Fertilize newly planted blueberries 30 days after planting with ammonium sulfate at 1 oz/plant placed in a ring 1 to 2 feet from the plant. If phosphorous or potassium are required based on a soil test, they should be applied before planting and tilled into the soil. They may be added before or after planting. Increase the amount of nitrogen by 1 ounce every two years until the eighth year, then decease it to 3 oz/plant in future years.

Brambles such as raspberries and blackberries can also be fertilized in the absence of a soil test with 12-12-12 at a rate of 1 to 2 pounds per 100-foot row. This amount can be repeated in the spring before growth starts until the third year, then increase the amount to 5 to 6 pounds per 100-foot row. After many years using this option, phosphorous and potassium levels in the soil can build to the point that only annual nitrogen applications will be required. A soil test every three years will help to monitor the situation. If a well-established patch requires nitrogen only, apply and water in 1.3 to1.5 pounds per 100-foot row urea (46-0-0), or substitute dried blood meal 13-0-0 or corn gluten meal 10-0-0 using the same rate as 12-12-12 if an organic source is preferred.

Fertilize grapes with a balanced fertilizer at a rate of 1lb/plant placed in a ring 2 to 3 feet from the trunk. If no phosphorous or potassium are required, urea (46-0-0) may be used at 4 oz/plant. Apply fertilizer in mid- to late April. It is also beneficial if the application is timed just before rain. Established plants may require 1 to 2 pounds of urea annually spread in a 5-foot ring around the plants. Organic sources may be substituted for urea as long as you compensate for the lower amount of nitrogen in the organic sources.

A smart gardener knows that proper fertilization based on soil test results will result in healthier and more productive plants while protecting Michigan’s water resources from pollution. So take the time to grow it right!

Related MSU Extension article

• “Fertilizing your vegetable garden”