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Garden Guru: Prepare trees and shrubs for the big sleep

By John Porter

CHARLESTON, W.Va. -- As the gardening year rolls to a stop, it is time to think about preparing trees and shrubs for their winter sleep so they'll awaken refreshed and ready to get to business once the blush of spring calls them to attention.

It may sound silly to say that now is the time to concentrate on caring for trees and shrubs, when they are getting ready to go into their winter dormancy. But what we don't often realize or see is that the trees are never fully asleep in the winter. Plus, some basic care now will help avoid winter damage that can kill branches and deaden entire areas on some shrubs.

Fertilize in the fall

While trees and shrubs may lose their leaves or stop growing aboveground for winter, the roots are still growing beneath the soil and pulling up water and nutrients when the soil isn't frozen. They take the focus away from the top of the plant, and instead take a little time to rebuild and replenish. It's almost like a tree meditation retreat. To facilitate this growth, the fall is the time to fertilize trees so that they have a sufficient amount of nutrients available as building blocks.

Root growth is particularly encouraged by the presence of phosphorous, the second number in the "big three" N-P-K ingredients you'll find on the bag of fertilizer. Potassium (the K at the end of that list) also plays a part in overall plant growth. Nitrogen, which is listed first, can be applied in the fall, but it directs growth of the leafy, green parts of plants and at least some should be applied in the spring.

To quote my friend and colleague Chuck Talbott, the extension agent in Putnam County, when you talk about the N, P and K on the fertilizer bag, remember the phrase "up, down and all around."

What and how to fertilize

Of course, the best answer to how much fertilizer to apply would be answered with a soil test, which I have discussed in previous columns. But, barring that, you can still make applications of fertilizers based on basic recommendations. A balanced granulated fertilizer, such as 10-10-10, is a good place to start. If you prefer to use another fertilizer, such as an organic, you'll need to adjust the rate of application to get the desired amount of actual nutrient applied.

Every time I visit a garden center, I see the tree fertilizer spikes sitting on the shelf and cringe. These spikes, which supposedly make it easier to fertilize trees, do more harm than good. Each individual section of root feeds one very specific part of the tree crown. If you direct a majority of fertilizer to one point, which is what the spike does, you feed specific spots of the crown while others starve. The result is what I refer to as tree "bed head." Just don't do it.

When you apply the fertilizer, traditional wisdom has stated that you apply fertilizer out to the drip line, which is where the span of branches end. However, more updated thought says that you should apply fertilizer up to twice the diameter beyond this. Roots can reach out a great distance, so you'll want to make sure you feed them all.

There are a few ways to calculate the rate of application of your fertilizer. The first is to measure the diameter of the tree, and apply 1 to 2 pounds of a 10-10-10 fertilizer (or equivalent) for every inch of tree diameter. Trees less than 6 inches in diameter should get 2 pounds. The second method is to calculate the area where you are applying fertilizer and apply 10 pounds of 10-10-10 for every 1,000 square feet (that's a lot of 1's and 0's -- I thought I was writing computer code for a minute). For those with smaller trees and shrubs, that works out to 1 pound (2 cups) per 100 square feet or 4 tablespoons per 10 square feet.

Still need to water

Because the roots of trees and shrubs are still actively growing and pulling water and nutrients from the soil, it goes without saying that they still need water during fall and winter. If there is an extended dry period, especially in the fall, it is a good idea to deeply water trees and shrubs so they can take up as much water as they can before the process slows. Even in winter, during warmer sunny days, trees can still take up water. In fact, they need to.

Winter damage on trees and shrubs is caused by drying out, not by freezing. Cold, dry winter winds dry out leaves and needles on evergreens and even twigs and branches on deciduous trees. When there is sun and warmth in the winter, trees and shrubs with leaves and needles will lose water to transpiration, so they need water to keep from drying, and dying, out.

John Porter is the WVU Extension Service agent for agriculture and natural resources in Kanawha County. He may be reached at john.porter@mail.wvu.edu or at 304-720-9573. Twitter: @WVgardenguru.


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