Ag Notes: November, December ideal time to fertilize landscape plants

September 30, 2003|JERRY LITTLE

Late fall and early winter are the best times to fertilize landscapes with mixed plantings of grass and woody plants. But how much fertilizer should you apply?

First, take eight to 10 soil samples from several areas of the yard. Mix the samples together and take them to the Boyle County Cooperative Extension Service office to be submitted for analyses to determine soil pH (soil acidity or alkalinity) and whether you need to apply other necessary nutrients including phosphorus and potassium. You will receive research-based recommendations on the fertility needs of your landscape. There is a nominal fee for a soil test.

It's especially important to have a soil test done before you set out trees and establish lawns so you can add needed amendments prior to planting. For an existing landscape, take samples from only the upper three to four inches of soil. Remove any thatch or plant debris from the mixed sample before submitting it.


Nitrogen is the most common element applied with landscape fertilization. However, soil tests don't give recommendations for nitrogen because it is rapidly lost through leaching or is removed during plant growth.

Deciding how much nitrogen to apply depends on the level of growth and maintenance you want. For average, healthy growth, apply two pounds of actual nitrogen per 1,000 square feet. Apply four pounds of actual nitrogen per 1,000 square feet for more lush growth, which also will require a higher level of maintenance.

It's important to note that application recommendations are pounds of actual nitrogen, while a fertilizer bags lists the amount of nitrogen (first of the three-number analysis) as a percentage. A common lawn and garden fertilizer (10-10-10) contains 10 percent nitrogen so you would need to apply 10 pounds of fertilizer to get one pound of actual nitrogen.

You would need to apply 31/3 pounds of ammonium nitrate, which is 33 percent nitrogen, to get one pound of nitrogen. Urea contains more nitrogen, 46 percent, so you would get roughly one-half pound of nitrogen for every pound of urea applied.

There are several reasons late fall through early winter is the optimum time to apply nitrogen to yards with a mixture of grass and woody plants.

Applying nitrogen to grass in the spring and summer usually promotes excessive growth that's more susceptible to drought, disease and heat. Fertilizer applications to woody plants before they go dormant might interfere with their ability to become cold hardy. Most woody ornamentals lose leaves, indicating dormancy, by Nov. 1.

This is why November and December applications usually are best.

You can split fertilizer applications into two or three parts applied four to six weeks apart. For example, if you want to apply four pounds of actual nitrogen, make two applications each of two pounds of nitrogen, say in early November and again in early December. You also could make three one-pound nitrogen applications in early November, late November and finally in mid-to-late December.

For more information, contact the Boyle County Cooperative Extension Service.

Jerry Little is Boyle County extension agent for agriculture/natural resources.

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