For:
By: Daniel E. Mullins
Extension Horticulture Agent
The Pros and Cons of Fall Fertilization
Should you fertilize the lawn and shrub beds during the fall? Some say yes and some say no. I say, it depends.
The permanent plants in the landscape are as the name implies, in place for many years and should be maintained differently than seasonal plantings such as annual flowers and vegetables. Once the lawn and shrubs have been well established, the goal should be to apply just enough fertilizer to encourage moderate growth and good color.
I see more damage done from the excessive use of fertilizer than I do from the lack of it. Practice moderation when fertilizing. If too much is used the result can be excessive growth, the increased need for mowing and pruning, increased water use, more pests problems and a greater possibility of winter injury.
An application of fertilizer in the fall can be either helpful or harmful, depending upon the product that is used, the rate and the timing.
The fertilizer product that is used is extremely important. If any major element is lacking in our sandy coastal soils during the fall it is usually potassium. This is the element that is said to contribute to the overall health of plants and when present in optimum amounts, contributes to cold tolerance.
A review of September soil test results from local lawns and landscapes shows that in most cases potassium is low in the fall. This is partly due to the fact that many fertilizers currently being used are relatively low in potassium. Another reason is that most of the sources of this element are in a soluble form and have leached out of the root zone by this time of year.
A product for fall fertilization should therefore be one that is relatively high in potassium, or potash and low in nitrogen and phosphorus. Avoid the use of high nitrogen containing fertilizers at this time of year. The last thing that the gardener wants is to stimulate growth with nitrogen during mid to late fall. This literally sets the lawn and shrubs up for cold injury. Read the fertilizer bag carefully before purchasing. The elements are listed in this order: nitrogen, phosphorus and potassium. If it is high in the first two, it is not recommended for fall fertilization in the deep south.
The time that fall fertilization is done is equally important. In order to gain maximum benefits from an application of potassium, it must be available in time for assimilation by the lawn and shrubs before winter. In our area, make the application no later than September. Potassium applied to grass later when it is nearing, or in a dormant state would have little or no effect.
Be careful when applying potassium. Most forms dissolve quickly and can burn grass and shrubs if applied in excessive amounts. Be certain to water thoroughly after the application to activate the product and rinse it from foliage.
Note 1: Soil testing during late summer would more accurately answer the fall fertilization question.
Note 2: