A healthy lawn requires specific nutrients that it gets from the soil. Sometimes, though, your lawn needs an extra boost from a quality fertilizer to replace lost nutrients, stimulate leaf and root growth, and recover from wear and tear.
The Role of Soil
Soil produces nutrients when its microbes break down biodegradable material such as grass clippings, mulched leaves, cast off stems and roots, thatch, and dead insects and microorganisms into substances the grass can use. However, eventually this natural process can’t consistently produce enough food for your lawn without the help of a fertilizer. A lawn that isn’t fertilized will deteriorate over several years to one that’s thin, full of weeds, and prone to disease.
Important Lawn Nutrients
Grass gets the carbon, hydrogen, and oxygen it needs to grow from water, and carbon dioxide in the air. The other nutrients are found in the soil, where they’re absorbed by the root system — they’re divided into macronutrients and micronutrients.
There are three main macronutrients that are the most commonly used ingredients in lawn fertilizers:
- Nitrogen (N) for protein synthesis, leaf development, rapid growth, and chlorophyll formation.
- Phosphorus (P) is important in early root growth, accelerates maturity, encourages flowering, and helps seed formation.
- Potassium (K) plays a role in root growth and stem development and increases disease and drought resistance.
The NPK content, in that order, is always printed on the front of fertilizer bags as a series of three numbers (the letters N, P, and K are not always there). Each number gives the percentage by weight of that nutrient compared to the total weight of the bag.
For example, the numbers 24-8-16 on the front means the bag contains 24 percent nitrogen, 8 percent phosphorus, and 16 percent potassium. The NPK ratio is 3:1:2.
Other macronutrients include calcium (Ca) carbon (C), hydrogen (H),
magnesium (Mg), oxygen (O), and sulphur (S). If the fertilizer you buy contains these, they’ll be listed elsewhere on a label in percentages.
Micronutrients (trace elements) include boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn). These are also essential for plant growth but are only needed in minute amounts. They’ll also be listed as percentages on a label if your fertilizer contains them.
Before buying a fertilizer, get a soil test to determine the best NPK ratio for your lawn. If the test results show that all three nutrients are present in approximately equal amounts, purchase an all-purpose fertilizer with a 1:1:1 ratio. Popular NPK options for this ratio are 5-5-5 and 10-10-10, but keep in mind that the nutrients are twice as concentrated for the 10-10-10 fertilizer. You only need to apply half as much as with the 5-5-5 to provide the same level of nutrients.
On the other hand, if the test results show that your soil contains too much or too little of one or more of the three key nutrients, you can buy a fertilizer with a specialized ratio. For example, fertilizers are available with an NPK value of 16-4-8, which is a 4:1:2 ratio. Or get one with an NPK value of 10-0-0 that has no phosphorus or potassium if that’s what your soil needs.
According to the Texas A&M AgriLife Extension Service, if you need to fertilize before you can get your soil tested, apply a fertilizer with 4 to 6 parts nitrogen, 1part phosphorus, and 2 to 4 parts potassium.
Types of Fertilizer
There are two main fertilizer types: organic and synthetic.
Organic fertilizers are made from plant or animal waste, or powdered minerals, such as compost, manure, cottonseed meal, bone meal, or rock phosphate. They usually contain plant nutrients in low concentrations and tend to have more micronutrients. Many of these nutrients have to be converted into inorganic forms by soil bacteria and fungi before they can be used, so organic fertilizers take longer to improve your lawn.
As well, organic fertilizers add beneficial microorganisms to the soil to help improve its structure and ability to hold water and nutrients. And because of the way they work, it’s difficult to over-fertilize and kill (burn) your grass.
Organic fertilizers are available in liquid and dry forms (e.g. pellets, powders). Liquid examples include fish, kelp, and extracted compost teas. The liquids produce short-term, rapid results when grass needs a quick boost for green up, but they don’t provide the same benefits to the soil structure or promote the growth of microbial life as do the dry forms. Some dry form examples include manure, compost, greensand (an iron potassium silicate), and all the plant meals, such as corn gluten meal.
Synthetic fertilizers are made in factories to exact specifications with specific nutrients — usually nitrogen, phosphorus, potassium, sulfur and sometimes micronutrients, either separately or in combination. They’re available in liquid and granular forms.
The form of nitrogen in synthetic fertilizers determines whether they’re quick-release or slow-release.
- Nitrogen that’s water-soluble (WSN).
- Immediately available to plants when dissolved by irrigation or rainfall.
- Typically includes materials like ammonium nitrate, ammonium sulfate, and urea.
- Stimulates quick shoot growth and greening.
- If over-applied can “burn” or kill grass.
- Needs to be applied more often.
- Nitrogen that’s water-insoluble (WIN).
- Releases gradually over a longer period of time.
- Includes materials such as isobutylidine diurea (IBDU), sulphur-coated urea (SCU), methylene urea, polymer-coated urea (PCU), and urea formaldehyde (UF).
- Provides more uniform grass growth.
- Lasts longer and requires fewer applications.
- Less likely to “burn” grass.
- More expensive per pound.
Information on the fertilization label should tell you whether the nitrogen is quick or slow-release. The percentage of the bag that’s slow-release should be listed — choose a fertilizer with a high percentage. If this information isn’t listed, then the fertilizer is quick-release.
A bridge fertilizer is a blend of synthetic nitrogen with mostly organic matter, giving it a variety of quick and slow-release nitrogen materials. This allows you to boost growth, while at the same time provide your soil with the benefits of organic fertilizers.
When to Apply Fertilizers
The best time to apply the first nitrogen-rich fertilizer is when the grass is actively growing and able to make use of the fertilizer. For warm-season grasses this would be late spring after the grass has greened up and been mowed two or three times, and in the fall at least six weeks before the first expected frost.
Use your soil test results and a fertilizer calculator to help you match your soil test results with an appropriate fertilizer.
If using a slow-release fertilizer in the spring, read the label carefully to see how long it lasts. You need to leave enough time between applications so you don’t damage your lawn.
In the fall use a quick-release fertilizer. Applying nitrogen in the fall increases lawn density, improves color, helps prevent winter weeds, and aids in spring recovery.
If your lawn is newly established, or needs some extra help, you can also apply a fertilizer during the summer. Make sure there’s been sufficient time since the spring application, and that there’s enough time before the one in the fall. Don’t fertilize during a drought.
Be sure to apply fertilizer in accordance with the manufacturer’s instructions. Not only could too much fertilizer damage your lawn, but the excess can run off into storm drains and find its way into the groundwater and cause pollution of rivers and streams.
Sound irrigation practices are indispensable to a lush and healthy lawn. Call the licensed irrigators at Smart Earth Sprinklers at (512) 694-1147 or contact us online to keep your sprinkler system operating at its best.