WEED AND FEED NOT FOOLPROOF by Larry Williams, UF/IFAS Extension Agent

The weed and feed concept is popular. Fertilizing a lawn and controlling weeds at the same time sounds like a winning combination. But be cautious, it’s not foolproof.

When the herbicide (weed killer) in a weed and feed product is a preemergent, the product must be applied prior to weed emergence. Applying a preemergence herbicide, after weed emergence (when weed seedlings are visible), will have litter or no effect. In general, a preemergence herbicide should be applied February 15 to March 1 in North Florida (when day temperatures reach 65º to 70ºF for four or five consecutive days). This will be about the time that azaleas and dogwoods first begin to bloom.

Many common weed and feed products contain fairly high amounts of nitrogen fertilizer. Nitrogen stimulates top growth in lawns. Applying a high nitrogen fertilizer too early increases the likelihood of frost/freeze injury to the tender new growth induced by the early nitrogen application.

If the weed and feed is applied mid February to early March (as a premergence), it’s too early for the fertilizer. If it’s applied mid March through April (as a fertilizer), it’s too late for the premergence.

Many common weed and feed products contain too little potassium. Potassium is second only to nitrogen in utilization by turfgrass. Adequate potassium has been linked to reduced disease problems, drought and cold tolerance and enhanced root growth. A good fertilizer for Florida lawns contains a 2:1 or 1:1 ratio of nitrogen (N) to potassium (K). Examples of a 2:1 ration are 16-4-8 and 16-0-8. Examples of a 1:1 ratio are 15-2-15 and 10-0-10. There are others.

Additional concerns with the weed and feed approach:

  • Does not lend itself to spot treatment of small weed infested areas in a lawn.
  • Does lend itself to blanket application of the herbicide, even where weeds aren’t a problem-because the herbicide is mixed with the fertilizer.
  • Herbicide can easily end up on paved surfaces and ultimately in water ways.
  • Many weed and feed products contain too much nitrogen and too little potassium;
  • Herbicide in many weed and feed products can injure nearby trees and shrubs.
  • Overuse of some preemergence herbicides can result in stunted lawn roots.
  • Preemergence herbicides can interfere with lawngrass seed germination.
  • Some preemergence herbicides can severely injure newly sprigged lawns.

Give these considerations some thought and you may decide to do your weed control and fertilization separately.

It is the user’s responsibility to read and follow all label directions and precautions when applying any pesticide, including herbicides in weed and feed products.

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