When to Fertilize
A good fertilization schedule is without a doubt critical to the success of any lawn. There are many recommendations on specific lawn fertilization schedules. Whenever available I have added these schedules to the pages associated with the individual species in question. As a rule, general purpose commercial lawn fertilizers are acceptable for most lawn grasses. One of the rare exceptions to this rule is centipede grass, which is not tolerant of phosphorous (the middle element in fertilizer labels). This is the reason why a fertilizer such as 15-0-15 is recommended for centipede.
Fertilizers have labels which show what percentage of each element is available in that particular blend. This is expressed as N-P-K (N for Nitrogen, P for Phosphorous and K for Potash). So a Fertilizer with a label of 10-6-6 consists of 10% Nitrogen, 6% Phosphorous and 6% Potash. When buying fertilizer for your lawn you should take into consideration local requirements, ideally (although rarely done) I soil test through your local agricultural extension would be ideal.
There is a key factor in fertilizer recommendations which you will find through out this website. It is an expression of how much nitrogen is required on an annual basis per 1000 Sq Ft. It sounds more complicated then it really is. The easiest way to explain this is by example. Suppose you are looking at a fertilizer with a value of 10-10-10. The first element is Nitrogen. If you divide 100 by that number you will get the number of pounds of that fertilizer that you need to apply per 1000 Sq Feet per year to get a value of 1 pound of nitrogen. So if your lawn type requires 2 pounds of nitrogen per year, you would need to apply a total of 20 pounds of fertilizer (using the 10-10-10 example) for the entire year.
Example for a 10-0-10 Fertilizer
|Divide 100 by 10||10 pounds per 1000 Sq Ft to apply 1 pound of Nitrogen|
|Lawn Requirement||Number of Pounds of Fertilizer per 1000 Sq Ft to apply|
|2 Pounds per year||20|
|5 Pounds per year||50|
|10 Pounds Per Year||100|
Annual Application Rates By Grass Type
|Grass Type||Annual Nitrogen Requirement (Pounds per Year per 1000 Sq Ft)|
Another factor to consider when buying fertilizer is the release rate. A fertilizer with a slow release rate is preferable. Whether the grass is a warm or cool season grass is also important in establishing a good fertilization schedule for your lawn. Typically, the warm season grasses are safe to fertilize during summer months. The cool season grasses are as well but only in the northern zones. Fescue is particularly prone to stress when fertilizing during the summer months and especially so in the deep south.
Lawns such as Centipede may require additional iron. Iron will help Centipede as well many other varieties develop a darker green color. Some fertilizers already have iron in them, if the fertilizer you are using does not you may want to consider adding it separately if your grass type requires it (refer to the specific grass sections for more information on your grass type). Lack of iron can cause a condition in grasses called Iron Chlorosis, this iron deficiency will cause the grass to turn yellow.
Iron can be added via a few different methods. Some fertilizers have an iron amendment added to them. There are also amendments such as ironite and Bonide Liquid Iron (either chelated or as Ferrous Sulphate). For the Do-it-yourselfer you also have the option of buying Ferrous Sulphate in bulk, it is quite inexpensive, I have found sources on line where a nine pound pail costs $14.00. Since the recommended rate of application is 1 tablespoon per 3 gallons of water per 1000 Sq Ft that $14 pail will go a very long way. Chelated Iron is a bit more expensive then ferrous sulphate but will last longer. Bonide makes a liquid form of this called “bonide Iron Liquid Chelate” which is actually a complex of essential minerals/metals.