Fertilizing Your North Florida Lawn

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Lawn Fertilization Calendar -                    When to Apply Fertilizer

Lawns can benefit greatly from fertilization, but can also be damaged or killed by applying too much fertilizer or applying fertilizer at the wrong time of year.

The following is a basic fertilizer schedule for lawns in North Florida maintained without the benefit of a soil test.  However, it is always recommended to conduct a soil test before fertilizing in order to properly apply the rate of phosphorus (P) and potassium (K) required.  For the initial Spring application, particularly in North Florida, the recommended time to fertilize is after the last frost rather than on a specific calendar date.

  • April - Complete Fertilizer (N, P, K)
  • June - Iron Only* (Iron Sulfate or Chelated Iron)
  • Sept - Complete Fertilizer (N, P, K)

Some lawns, such as Centipedegrass, may only need one fertilizer application in the Spring.  Others may not require an iron application during Summer.  Soil Testing will provide specific recommendations tailored to your lawn.  For more information on lawn fertilization and to view a more detailed fertilizer calendar for specific lawn types in areas across Florida, visit General Recommendations for Fertilization of Turfgrasses on Florida Soils.

*Apply Iron (Fe) to provide dark green color without stimulating excessive growth.  For foliar application use ferrous sulfate
(2 oz / 3-5 gal water / 1000 sq ft).  If the Fe is applied to an acidic soil, use one pound of iron sulfate per 1000 square feet.  If the soil is calcareous, use the container label recommended rate of an iron chelate.

Selecting a Lawn Fertilizer

 
What do the numbers on the bag mean?

The three numbers printed in very large numerals on the bag represent the amounts of nitrogen (N), phosphorus (P as P2O5), and potassium (K as K2O) in the bag.

These numbers represent the percentage of each nutrient or the number of pounds of each nutrient in a 100 pound bag.  For example, a 16-4-8 fertilizer contains 16% nitrogen (N), 4% phosphorus (P), and 8% potassium (K).  This also means that in a 100 pound bag of 16-4-8 fertilizer, 16 pounds is actual nitrogen (N), 4 pounds is actual phosphorus (P), and 8 pounds is actual potassium (K).

 What fertilizer analysis is best for my lawn?

To determine the fertilizer analysis (N-P-K) that is best for your lawn, a soil test should be conducted.  Soil testing is available through your local county Extension office. 

Where a soil test does not exist, we recommend using a 15-0-15, 10-0-10, 16-2-8, or similar fertilizer. 

 A general rule of thumb when selecting a lawn fertilizer is to choose a fertilizer containing a 1:1 to 2:1 ratio of nitrogen (N) to potassium (K).  This means that the fertilizer contains equal amounts of N (1st number) and K (last number) OR no more than twice as much N as K. 

Another general rule of thumb when selecting a lawn fertilizer is to choose a fertilizer with zero P (2nd number), unless you have a soil test report that recommends adding this nutrient.  This is because phosphorus tends to be prevalent in Florida soils and is often responsible for water pollution when over-applied.

What is the difference between slow-release and quick-release nitrogen fertilizer sources?

Most home-lawn fertilizers contain “slow-release” nitrogen, which means that the nitrogen is available to the lawn over an extended time, rather than all at once. Many fertilizers that contain “slow-release” nitrogen provide fertilization for 60 days or longer, depending on environmental conditions and the percentage of slow-release nitrogen.

 A slow-release fertilizer contains at least 30% - 50% water insoluble (slow-release) nitrogen. 

 A quick-release fertilizer contains less than 30% water insoluble (slow-release) nitrogen.

 When following best management practices (BMPs), using a slow-release fertilizer allows the user to apply a greater amount of fertilizer to the lawn at any one time which reduces the amount of maintenance required.  Learn more about fertilizer application rates (how much fertilizer to apply) below. 

Fertilizer Application Rates –            How Much Fertilizer To Apply


How much fertilizer to apply at any one time depends on four things:

1 – The amount of total nitrogen in the bag

2 – The percentage of slow-release nitrogen in the bag

3 – The square footage of your lawn

4 Whether the turf is growing in shade (turf in shade will need less fertilizer)

Regardless of the level of maintenance you desire, always adhere to these guidelines using the charts below followed by proper water management.  The potential for leaching or runoff of nutrients in fertilizer is directly related to the amount of water, either from irrigation or rainfall, applied after fertilization.

Some irrigation is generally required to wash the fertilizer off the leaf blades, but too much water can wash the fertilizer past the root zone.  Once the fertilizer is past the root zone, the fertilizer won't be absorbed by the plant's roots.  Apply about a 1/4 inch of water to properly irrigate fertilizer.  The use of fertilizers is not recommended if heavy rainfall is forecast within the next 24 hours.

If you are applying a Quick Release Fertilizer (containing less than 30% slow-release nitrogen), use the following chart which explains the approximate weight of fertilizer to use for a given lawn area in pounds (first number) and also in cups (second number) to deliver ½ lb N per 1000 sq ft (the recommended rate for a single application of soluble or quick release fertilizer).

                     % Nitrogen in Fertilizer Bag

Area (sq ft)

6%

10%

12%

15%

16%

23%

27%

10

1.3 oz

3 TB

0.8 oz

1 ½ TB

0.7 oz

1 ½ TB

0.5 oz

3 ½ tsp

0.5 oz

1 TB

0.4 oz

2 ½ tsp

0.3 oz

2 ¼ tsp

50

6.6 oz

14 TB

4 oz

½ c.

3.3 oz

7 TB

2.7 oz

6 TB

2.5 oz

5 ¼ TB

1.7 oz

4 ½ TB

1.5 oz

¼ c.

100

13.3 oz

1 ¾ c.

8 oz

1 c.

6.7 oz

14 TB

5.3 oz

¾ c.

5 oz

10 ½ TB

3.5 oz

9 TB

3 oz

½ c.

1000

8.4 lbs

17 ½ c.

5 lbs

9 ½ c.

4.2 lbs

8 ¾ c.

3.3 lbs

7 ¼ c.

3.1 lbs

6 ½ c.

2.2 lbs

5 ½ c.

1.9 lbs

4 ¾ c.

1500

13 lbs

26 ¼ c.

7.5 lbs

14 ¼ c.

6.5 lbs

13 c.

4.9 lbs

11 c.

4.8 lbs

9 ¾ c.

3.3 lbs

8 ¼ c.

2.9 lbs

7 ¼ c.

3000

25.2 lbs

52 ¼ c.

15 lbs

28 ½ c.

12.6 lbs

26 c.

9.8 lbs

21 ¾ c.

9.4 lbs

19 ½ c.

6.6 lbs

16 ½ c.

5.8 lbs

14 ½ c.

5000

42 lbs

87 ¼ c.

25 lbs

47 ½ c.

21 lbs

43 ½ c.

16.4 lbs

36 ½ c.

15.8 lbs

32 ½ c.

11 lbs

27 ½ c.

9.8 lbs

24 ½ c.

 

If you are applying a Slow Release Fertilizer (containing 30-50% slow-release nitrogen), use the following chart which explains the approximate weight of fertilizer to use for a given lawn area in pounds (first number) and also in cups (second number) to deliver 1 lb N per 1000 sq ft (the recommended rate for a single application of insoluble or slow release fertilizer).

                    % Nitrogen in Fertilizer Bag

Area (sq ft)

6%

10%

12%

15%

16%

23%

27%

10

2.6 oz

6 TB

1.6 oz

3 TB

1.4 oz

3 TB

1 oz

2 TB

1 oz

2 TB

0.8 oz

1.5 TB

0.6 oz

1.5 TB

50

13.2 oz

1 ¾ c.

8 oz

1 c.

6.6 oz

14 TB

5.4 oz

12 TB

5 oz

10 ½ TB

3.4 oz

9 TB

3 oz

½ c.

100

1 ½ lbs

3 ½ c.

1 lb

2 c.

13.4 oz

1 ¾ c.

10.6 oz

1 ½ c.

10 oz

1 ¼ c.

7 oz

1 1/8 c.

6 oz

1 c.

1000

16.8 lbs

35 c.

10 lbs

19 c.

8.4 lbs

17 ½  c.

6.6 lbs

14 ½ c.

6.2 lbs

13 c.

4.4 lbs

11 c.

3.8 lbs

9 ½ c.

1500

26 lbs

52 ½ c.

15 lbs

28 ½ c.

13 lbs

26 c.

9.8 lbs

22 c.

9.6 lbs

19 ½ c.

6.6 lbs

16 ½ c.

5.8 lbs

14 ½ c.

3000

50.4 lbs

104 ½ c.

30 lbs

57 c.

25.2 lbs

52 c.

19.6 lbs

43 ½ c.

18.8 lbs

39 c.

13.2 lbs

33 c.

11.6 lbs

29 c.

5000

84 lbs

174 ½ c.

50 lbs

95 c.

42 lbs

87 c.

32.8 lbs

73 c.

31.6 lbs

65 c.

22 lbs

55 c.

19.6 lbs

49 c.

 

For more helpful information on lawn care, refer to Your Florida Lawn, a collection of fact sheets on residential lawns.