Tree Fertilizing Facts #GardenSense

The best time to plant a tree was 20 years ago. The second best time is today. — Chinese Proverb.
But what about fertilizing your trees?

Tree Fertilizing Facts

Taking care of trees can be a mystery to many gardeners; especially when it comes to fertilizing. Most plants get their first dose of fertilizer in the spring when new growth appears. But does this rule apply to trees?

Not according to experts with the American National Standards Institute (ANSI).

Here are a few little known facts taken from a recent east coast conference:

Trees hoard nitrogen. When a tree receives nitrogen off-season, it will store this nutrient in its limbs and stems until needed. So the amount of nitrogen a tree needs at a given time is hard to determine. The best course of action is to know when to fertilize if needed so the tree receives nitrogen at the proper time.

Sound difficult? Its not really if you keep a few facts in mind.

Nitrogen leaches easily from the soil and is not considered measurable in a soil test. Since a soil test for trees can be deceiving, a fertilizer in 3:1:1 ratio, 3 parts nitrogen, 1 part potassium, 1 part phosphorus is best for trees when no soil test is done.

Trees need nitrogen when in full leaf production (May through July). Applying fertilizer in this time period will help get nutrients to the trees when they need it. So a slow release fertilizer applied at the soil surface works best.

Fertilizing increases pest problems. It was once thought that fertilizing anytime made healthy plants and healthy plants better fought off pests. Now researcher know it is all in the timing. High nitrogen content reduces tree defenses against insects. All the tree’s energy goes towards leaf production. This creates a great feeding environment for insect pests while lowering a tree’s natural defensive chemical production.

Spring fertilizing will create a food source for emerging larvae or caterpillars. One study showed that eastern tent caterpillars grew 530 percent faster on highly fertilized trees. Gypsy moths were also proven to grow faster and lay more eggs.

The best method for success with the least problems is to institute a pest management system. Getting pests under control or minimized before fertilizing will decrease the risk.

It is also important to remember that fertilizer is not “plant food”. Fertilizer is considered a salt-based nutrient. The yellowish-white crust on top of your houseplants is fertilizer salt. Excess fertilizer impedes the plant from taking up water and nutrients. New plantings will benefit from slow released fertilizer.

Your County Extension Office can help you determine how much fertilizer to use based on the time of year, type of tree, tree health and tree age.

So in conclusion, fertilizing a tree can be a trade off. Trees will grow faster and have more foliage, but be more susceptible to insect damage, drought and disease. Incorrect timing of fertilizing increases this risk and you may be spending more money and time on insect control.