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Fertilizers come in a dizzying array of formulations. Walk through the garden center at the local warehouse joint, and you'll be confronted with dozens of different products, each touting itself as the cat's meow for your lawn. You can cut through the hype and get the right stuff though, if you know what you're looking for.
Fertilizers can be divided into 5 categories: Growth, starter, balanced, complete and special need. These are categorized based on the amounts of Nitrogen, Phosphorous and Potassium in the bag, or the N-P-K ratio.
A growth fertilizer will have a high N content and relatively low P and K content. Ammonium nitrate is the highest Nitrogen fertilizer you can buy, and it is potent stuff. It is usually rated as 33-0-0 or 34-0-0. The bag contains 33% or 34% Nitrogen and the other 66% or 67% is inert material. Other formulations of growth fertilizers will contain 5, 6 or even 7 times more Nitrogen than anything else. Use growth fertilizers very sparingly, applying them lightly during the peak growing season of your grass.
A starter fertilizer is used to help a new lawn become established. They contain very small amounts of Nitrogen relative to the other two nutrients, and you will often see them in a 5-20-20 formulation. New lawns need extra Phosphorous and Potassium to develop strong roots and resist disease, but they also need a tad of Nitrogen for growth. Use these fertilizers as recommended on your seed package, or as recommended in a soil analysis conducted prior to planting.
Balanced fertilizers are just what they sound like--the amount of nutrients contained in the bag are balanced. You will see these as 6-6-6, 8-8-8, 10-10-10, etc. Unless a soil analysis has shown that your soil is deficient in all three nutrients, your lawn will rarely need a balanced fertilizer. These are better suited towards other plants in your landscape, such as trees, shrubs, annuals, perennials and vegetables.
Complete fertilizers have 3 or 4 times as much Nitrogen as Phosphorous and 2 times as much Nitrogen as Potassium. In most cases, this is the stuff your lawn will use best. They are called "complete" because they provide nutrients in a mix that completely satisfies most grass' requirements. If you only make one or two fertilizer applications a year, this is the stuff you want.
Special need fertilizers are formulated for the requirements of specific grass types, such as Centipede, or to correct a soil deficiency problem. 15-0-15 is the only fertilizer you should use on Centipede. 0-0-60 is used to correct severe Potassium deficiencies, and 0-40-0 is used to correct phosphate poor soil. Unless you have Centipede, you should have your soil analyzed by the extension service in your county before buying and using a special need fertilizer.
You've been told to apply 1 lb of Nitrogen per 1,000 square feet. How do you determine how much fertilizer you need in order to get 1 lb of N per 1,000 sq.ft?
Divide the first number in the fertilizer analysis into 100. For example, you have a 1,000 square foot stand of turf that requires 1 lb. of Nitrogen in a complete formulation. Your fertilizer is 16-4-8, so you just do the math:
100 / 16 = 6.25
You need 6.25 lbs of fertilizer.
Weed and Feed products need certain conditions in order to be effective. If you are sure of these conditions, this is a very effective tool. If you are not sure, or if your timing is wrong, the product will not work as it was designed. Make sure that:
Contact with weed leaves is good. Don't mow just before applying--instead, mow it a few days beforehand. This stimulates weed growth.
The problem weeds are broadleaf weeds. Grassy weeds, like crabgrass and dallisgrass, require different products.
The problem weeds are young and actively growing. Mature weed plants are just gonna laugh at you.
Rainfall or irrigation won't wash the herbicide off of the leaf. Don't water after applying broadleaf weed control products, and don't apply them if there is a chance of rain in the forecast.
The temperature is right. Average daily temperatures should be above 70 but below 85. The best time to apply a weed and feed product is in early spring, after the danger of frost but before the weeds have matured.
Most grasses, like all living things, do best when their nutritional requirements are met "completely." This has given rise to the formulation of so-called "complete" fertilizers. Such products will contain four times as much Nitrogen as Phosphorous and twice as much Nitrogen as Potassium. This 4-1-2 formulation is often sold in a 16-4-8 analysis, and includes trace minerals and nutrients, such as Iron and Zinc. Avoid the heavy, repeated use of high Nitrogen fertilizers, which contain 5, 6, even 7 times as much Nitrogen as anything else in the bag. Applying these will get the desired short term results--the grass will develop a lush green canopy. But overdoing it will have predictable long term results. The grass will not be able to develop the root system it needs to support that canopy, so the grass will be more susceptible to drought. The grass will also not be able to develop a capable immune system, so the lawn will be more susceptible to disease. Diseased, drought stressed turf is then a favored target of insect pests. Two applications of 16-4-8 per year--once in spring, once in early fall--will provide very good color and growth for your St. Augustine, Bermuda or Zoysia lawn (Centipede needs a special fertilizer). If additional color and growth is desired, light applications of high Nitrogen fertilizers can be made through the growing season.
These products are different than Weed and Feed products for other grass types. They usually contain Atrazine or Simazine, both of which are pre-emergent herbicides. They do not need to make contact with the weed plants, and they tend to last longer. Applying them anytime after the grass has fully greened up is Ok. Make sure you read and follow label directions carefully. If the fertilizer component of your product is NOT 15-0-15 or some other 1-0-1 formulation, DO NOT use it. Centipede can be killed by fertilizers designed for other grass types.
Centipede has a lighter green color that is very different than either Bermuda or St. Augustine, both of which show a darker green hue that many homeowners yearn for. Unhappy homeowners often try to "push" Centipede to put out greener growth through the use of high Nitrogen fertilizers. Don't do it. The grass will green up, but the lush new growth will be irresistable to lawn pests and only lead to thatch formation down the road. Instead of trying to push your grass with too much Nitrogen, try applying some Iron instead. The grass will green up very nicely, but you won't have the pest or drought stress problems. In my experience, 95% of the disease, insect and drought stress problems in Centipede lawns are caused by over-fertilization. Even using the wrong fertilizer can cause problems in Centipede. Whereas most grasses do well using complete fertilizers (like 16-4-8 or sometimes 12-4-8), Centipede needs only trace amounts of Phosphorous. Thus, fertilizer companies have developed a 15-0-15 analysis that contains 2% or 3% Iron. Look for it. Apply it once, maybe twice a year at 7 lbs per 1,000 square feet of turf.
These products are different than Weed and Feed products for other grass types. They usually contain Atrazine or Simazine, both of which are pre-emergent herbicides. They do not need to make contact with the weed plants, and they tend to last longer. Applying them anytime after the grass has fully greened up is Ok. Make sure you read and follow label directions carefully.
You don't need to use chemical fertilizers if you don't want to. There are numerous naturally occurring substances that will supply the nutrients your lawn needs. One of the most easily obtained is the bag of clippings from your lawn. Grass clippings are rich sources of Nitrogen, Phosphorous and Potassium, the nutrients your grass needs the most of. Because they are stored in plant tissue, decomposition of grass clippings slowly releases the nutrients to the turf. If you have a mulching mower, mow your lawn frequently and leave the clippings on the lawn.
Unless a soil analysis has recommended the application of another fertilizer, you should only use 15-0-15 on Centipede. Why? Because Centipede does not need Phosphorous (the middle number) in more than trace amounts. If your soil is slightly alkaline, the Phosphorous can lock Iron up in the soil, causing the grass to suffer Iron chlorosis and turn yellow. You should not use high Nitrogen fertilizers on Centipede, either. It thrives under low fertility conditions and will do just fine with a moderate amount of Nitrogen. If you try to push it with too much Nitrogen, it will develop a lush green canopy that cannot be supported by the rest of the plant. The lawn then becomes a target for pests and disease.
If your grass appears burned after you fertilized it, you may have used a quick release fertilizer. These should be avoided unless you know exactly what you're doing. Although they are more expensive, most people should stick with 'slow release' formulations. These are designed to release their nutrients slowly over a period of months (rather than hours), and if they're used according to the directions on the label, they won't turn your lawn brown.
If you have access to compost, or if you know the basics of composting, you can provide your lawn with a very slow acting, quite beneficial source of nutrients. A thin layer of composted plant matter will deliver small doses of vital nutrients over a long period of time. You will not get explosive growth, nor are you likely to maintain a dense lawn that completely crowds out weeds in a short period of time. However, over the long term your results will be just as effective as the high-tech approach.