October marks the end of most fertilizer restrictions in the Tampa Bay area. Most “summer bans” restrict the application of nitrogen and phosphorous from June 1st through September 30 during the rainy season. During the summer ban other nutrients such as potassium, magnesium, manganese, and iron can be applied. These other nutrients help turfgrass with resilience against disease and other stress, but they are not a substitute for nitrogen.

Nitrogen is needed for photosynthesis which uses sunlight to convert carbon dioxide and water into sugars. This process produces chlorophyll, which creates the green color in plants, and the biproduct oxygen. This is why your turfgrass may look a little pale after a nitrogen free summer.

Fall applications of fertilizer in central Florida should be completed by mid-November and no additional fertilizer applied until March of next year. During late fall and winter shorter daylight hours, reduced light intensity, lower temperatures, and less rainfall cause photosynthesis to dramatically slow. When photosynthesis slows the plant’s need for fertilizer and water are minimal.

But your turfgrass has been starving all summer making October and early November the ideal months to provide a good balanced meal before your turfgrass growth naturally slows.

Our warm season turfgrasses grow best at temperatures between 80-95° which typically occur between March and October. Growth slows and the need for fertilizer and water are minimal from October to March due to cooler nights and less sunlight. During this time nutrients are transferred from the shoots to the roots as stored energy for photosynthesis when spring brings warmer temperatures and longer days triggering growth. Since there is less sunlight for photosynthesis there is less need for water. Be sure to adjust your irrigation controller to provide irrigation only once every 10-14 days if there has been no rain. Also, make sure your irrigation rain shutoff device is working.

The following are lawn care recommendations for fall.

  • Utilize slow-release balanced fertilizer products with a 2:1 ratio of nitrogen (N) to potassium (K) and don’t use products with phosphorous unless a soil test indicates a deficiency. Example fertilizer analysis include: 16-0-8 or 24-0-11.
  • Potassium influences root growth, and water and stress tolerance. If your soil test shows a low potassium use a 1:1 ratio of N to K. Examples include: 15-0-15 and 18-0-18.
  • Use at least a 50% slow-release N fertilizer. This means that 50% of the N is released slowly over time (3-6 months depending on formulation) and 50% is quick release providing that quick green up.
  • Make the last annual fertilizer application by mid-November.
  • Make the first spring application in late March once the turf has begun to green up on its own.
  • Check your fertilizer label for irrigation requirement. Most granule fertilizers required a little irrigation after the application.
  • Apply no more than 1 pound of nitrogen at any one time and no more than 4 pounds of N over the growing season. Most turfgrass species do very well with much less N. To figure 1 pound of N divide 100 by the N analysis (the 1st number). This will give you the total pounds of that fertilizer to deliver 1 pound of nitrogen for each 1000 square feet of landscape. Example: For a 16-0-8 fertilizer, 100 divided by 16 = 6.25 pounds of 16-0-8 fertilizer per 1000 square feet to deliver 1 pound of nitrogen. If you have 2000 sq. ft. of lawn you need 12.5 pounds of 16-0-8 fertilizer. 3000 sq. ft. = 18.75 pounds.
  • Due to environmental conditions and/or improper care lawns may be susceptible to fall fungal disease such as large patch. Many diseases are promoted or made worse by too much water and high nitrogen fertilizers. For information on managing turfgrass disease click here.
  • If you have a history of winter weeds such as annual bluegrass, chickweed, henbit, lawn burweed or wild geranium you may need to apply a preemergent herbicide. A preemergent herbicide provides a chemical barrier in the soil that inhibits or kills weed seedlings when they come in contact. For more information on winter weed control refer to this weed control timeline.

Finally, know your local ordinance because in addition to the summer N and P ban, other year-round restrictions apply. There are restrictions regarding weather conditions, fertilizer free zones, and management of landscape debris. These restriction apply to all residents. In Hillsborough county there are penalties up to $500 and imprisonment up to 60 days for violations. Access the Hillsborough County Fertilizer Ordinance and Regulation webpage.

Visit the ProHort webpage.

Contact Susan at (813)744-5519 Ext. 54103 or szcrmchz@ufl.edu

by Susan Haddock

Source: UF/IFAS Pest Alert

Note: All images and contents are the property of UF/IFAS.

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