Understanding the science behind fertilizers is the first step to successful lawn fertilizing. Without some basic knowledge, you can severely damage or even kill your lawn by fertilizing incorrectly or using the wrong product. This article explains the basic elements found in fertilizers, the differences between organic and chemical fertilizers, and how to fertilize correctly.
There are three main ingredients in fertilizer - nitrogen, phosphorus, and potassium. Most fertilizers show the percentage of each ingredient as a series of three numbers on the front of the bag called the fertilizer grade. The first number indicates the nitrogen percentage, the second is the phosphorus percentage, and the third is the potassium percentage. These numbers show the percentage of the total product, so in a 10-10-10 mix, seventy percent of the product is other ingredients and fillers. Remember that when it comes to fertilizers, higher numbers do not necessarily mean a better product.
Nitrogen turns plants green and contributes to quick growth spurts. Nitrogen makes the most noticeable immediate change in plants. However, applying too much nitrogen or applying at the wrong time can weaken plants by causing overactive growth and taking nutrition away from the roots.
Phosphorus contributes to healthy roots, flowers, and seeds. Used in higher quantities for fruit and vegetable growth, phosphorus is not as necessary for grass and is only needed in larger percentages for new lawns. Additionally, certain areas of the United States have begun to enforce limitations on the amount of phosphorus that can be applied to established residential lawns due to its overuse and harmful effects it can have on lakes and streams.
Potassium provides nutrition to every part of the plant, and is especially important for new lawns and fall applications to help your lawn survive the winter. Potassium also helps nitrogen to be absorbed more efficiently. Low levels of potassium can lead to susceptibility to lawn diseases and environmental stresses.
In order to truly know which product is right for your lawn, you should perform a soil test through your local extension (part of the Cooperative Extension System, an education network through the U.S. Department of Agriculture) or purchase an at-home kit to perform a test yourself (Soil test kit, 266-5760). However, there are some general guidelines you can follow without knowing the chemistry of your soil. New lawns need a high amount of phosphorus and potassium to firmly establish their roots. Midsummer lawns need plenty of nitrogen and some potassium to help with the nitrogen absorption and overall health. Fall fertilizer should have high potassium to survive the winter, along with nitrogen to help early spring growth.
Some fertilizers include herbicide to facilitate weed control while you fertilize your grass. While this can be a convenient way to get out-of-hand weeds under control, keep in mind that all-over herbicide applications are not always necessary. Most weed problems can be controlled just as effectively with spot treatment applications that introduce fewer chemicals into the environment. Another issue with fertilizer-herbicides is the timing of application. For many weed types, herbicide would need to be applied when fertilizer isn't necessary. For these reasons, never use an all-over herbicide as a preventative measure if you do not have a weed problem.
Organic vs. chemical fertilizers
All fertilizers can be placed in one of two categories - organic or chemical. Each type has advantages and disadvantages and selection should be made based on your lawn's condition and personal preference.
Organic fertilizers usually remain in their original form as found in nature and usually come from plants and animals. They break down slowly and therefore greatly reduce the risk of fertilizer burn or using incorrect amounts of any nutrient. This also makes them environmentally friendlier. Organic fertilizers improve the soil structure permanently and increasing its ability to retain water and nutrients, whereas chemical fertilizers are a temporary solution and do not improve the soil conditions over time. However, since organic fertilizers are made of natural materials, it is difficult to know the exact chemical makeup of the product you are applying. Organic fertilizers can also be significantly more expensive than chemical fertilizers, so the additional cost must be considered.
Chemical fertilizers are fast-acting and their contents are perfectly calculated. They are less expensive than organic fertilizers. However, they have a greater negative impact on the environment. Chemical fertilizers are produced mainly from non-renewable resources, and, when overused, can affect water supplies. Over time, they affect the pH of the soil and can lead to increased pest infestation. If you use chemical fertilizers, make sure you are using the correct grade for your soil conditions and abide by any local or state laws on fertilizer use.
How to fertilize
While there are many theories on when to fertilize, a general rule is to only fertilize when your lawn is growing. Apply a fertilizer in spring (after the fourth mow) to give your lawn a boost as it begins the long growth season. Be very careful when applying a fertilizer in mid to late summer and make sure it is formulated for this season. Grass often goes dormant in dry summer heat and applying fertilizer can do more harm than good. In fall, when cooler temperatures and wetter weather return, grass will spring back to life and should be fertilized to give it the nutrients it needs to make it through winter. Many lawn care brands have a series of products to help you apply the correct product at the correct time (Menards® Premium 260-1590, 1593, 1595, 1621, 1623, 1629). Make sure you also use common sense when using these products and don't apply them if weather conditions are not ideal.
After selecting a fertilizer with the appropriate ratio of nitrogen, phosphorus, and potassium, check the fertilizer packaging for the calibration recommendation for your spreader. Always apply fertilizer to your lawn when the temperature is below 85 degrees. You can use a broadcast spreader or a drop spreader, and a handheld, walk-behind, or tow model (Yardworks Spreaders, 264-1222-2080). Each has its own advantages, but for someone new to fertilizing, a walk-behind broadcast spreader will usually make consistent fertilizing easiest to achieve. Make careful passes up and down your lawn, walking at an even pace. Do not overlap your passes as this can cause strips of fertilizer burn that will damage or kill your grass. Clean your spreader with water to prevent corrosion.
What to do when you've over-fertilized
As soon as you discover you have over-fertilized, begin watering the affected area. Continue watering until the soil will not take any more water. Water the area again every day for the next week. This will flush out as much of the fertilizer as possible. Do not attempt to correct the damage with additional applications of other products. If the grass is not saved, wait to re-seed until the following growing season, as the affected area might still spring back.