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Tree Talk: Spring is primetime for fertilizing trees. Here’s how to do it right.

Fredric Miller

February 18, 2022

2 Min Read
sun shining through green forest
Xurzon/Getty Images

What do you do in the spring? Apply fertilizer — even to your trees. Here’s what to remember.

1. Start with a soil test. Check the balance of soil nutrients and soil pH. Soil pH should be 6.0 to 6.5 for most plants. If it’s not, some nutrients may not be available for uptake, which will lead to poor plant health. If you have been regularly fertilizing your lawn with a complete fertilizer, you may have more than enough phosphorus and potassium in the soil. P and K are not used as quickly as nitrogen, and can build up in the soil to unacceptable levels. You may need to skip a season or two and apply an N-based fertilizer (no P or K) to allow levels to return to normal.

2. Time it right. Spring is a good time to fertilize because nutrients will be readily available right when your plants are breaking dormancy and starting to grow. Plants need large amounts of nutrients, particularly N, in the spring to provide energy for bud break, leafing out and shoot growth. Do not apply fertilizer when soil is dry! Fertilizers are salts and will pull moisture out of the roots and damage them. If you don’t have adequate soil moisture, irrigate prior to application.

3. Pair fertilizer rate with growth phase. The amount of fertilizer you apply depends on the age or growth phase of the plant. And remember — don’t fertilize trees if you’re already fertilizing turf under the tree’s dripline. General guidelines:

  • Recently planted ball and burlap tree. Back off on fertilizer and help establish roots with water and mulch for the first few years. It takes one year of growth for every inch of tree caliper — so a 2-inch tree will take two years of good growing conditions to regenerate roots.

  • Well-established plants. Annually apply N at 2 to 4 pounds per 1,000 square feet.

  • Mature trees. Apply 1 pound of N per 1,000 square feet every two to four years.

4. Don’t overapply. Nitrogen stimulates shoot growth over root growth. If the tree’s root system is not fully developed (newly transplanted) or not functioning optimally (mature or overmature trees), applying too much N will contribute to plant stress because the root system cannot support the canopy, which then can lead to all kinds of problems.

Miller is a horticulture professor at Joliet Junior College in Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at [email protected]. The opinions of this writer are not necessarily those of Farm Progress/Informa.

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