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Fall Fertilization for your Lawn

broadcast spreader throwing lawn fertilizer

Autumn is the prime time to fertilize your lawn, and yields substantial benefits over spring application. Fertilizing in spring causes rapid top growth but results in shallow root systems. In fall, adding fertilizer contributes to a healthier, deep root system. Fall-fertilized grass greens up earlier in spring and helps grass store energy allowing for more growth and disease resistance. Plus, healthy turf will crowd out many weeds and minimize the need for pesticide application. Plush, fertile lawns also reduce water runoff during heavy rains and storms. Begin fertilizing in October, after the daily average temperature drops to 50º. This can be determined by adding the daily high temperature and the daily low temperature, then dividing by 2. (Example: if your daily high temperature is 63º and your low is 36º, your average temp is 49.5º).

Choose your fertilizer

Begin with an inexpensive soil test and use the analysis will help you determine exactly what combination of nutrients you'll need. Fertilizers come with dozens of different formulations, and the understanding the label is important. Every package specifies the nutrients found in the blend. There, you'll find three numbers, each indicating the percentage of nutrients in the mix. Nitrogen is the first number, then phosphorous, then potassium. Superior Professional Lawn Fertilizer has a label reading 29-0-4, meaning it has a mixture of 29% nitrogen, 0% phosphorus and 4% potassium). A more general-use fertilizer like this Superior mix has a 10-10-10 number, indicating it has equal amounts of each nutrient. . If your soil test indicates a low soil pH, the application of lime can neutralize the soil, although most grasses in this area have adapted well to moderately acidic conditions. Check your local and state laws. In Wisconsin and Minnesota, you are prohibited from applying phosphorus to your lawn unless you are establishing a new lawn or have verified the need for it through a soil test. When excess fertilizer runs off your lawn, it can end up in local lakes and streams. Too much fertilizer in waterways can cause excessive weed and algae growth, poison fish and lower the oxygen levels in the water.

If you had been leaving grass clippings on your lawn to decompose all summer, good for you! Chances are the decomposing grass fed your soil, and your soil test will show that you will need much less nitrogen, as much as 40% less. In the fall, adding nitrogen will encourage root growth. Nitrogen also helps grass recover from injury and stress. Too little nitrogen leads to weed infestation and increased risk of disease. Nitrogen can be water soluble or water insoluble. The water soluble nitrogen acts quickly when applied, while insoluble nitrogen releases the nutrient over a period of time. Slower release is especially important for use on sandy soil, which leaches nutrients more quickly than heavy soils. Most fertilizers contain a mix of both soluble and insoluble nitrogen. Phosphorus is most useful for seed germination in new lawns, but usually is not required for established turf. Adequate levels of potassium help your grass tolerate stress and disease.


Using a broadcast spreader or a drop spreader will help you properly apply fertilizer according to the amounts specified on the package. If you have a calibrated spreader, be sure to use the formulas on the fertilizer package, and those provided with the spreader to assure that you have complete coverage. To apply fertilizer evenly with a broadcast spreader, use half the rate specified and apply in two passes, at right angles. To prevent fertilizer from getting into lakes and rivers, do not use a broadcast spreader near open water. Over-fertilization can result in problems with too much thatch. Sweep off excess fertilizer from paved surfaces. Mowing the grass a few days before applying fertilizer will let you to better see spreader tracks and determine your coverage area. To avoid waste and losing fertilizer to the wind, apply on calm days. Ideally, a slow steady watering (or rain) immediately after application will help move the fertilizer into the soil and prevent it from burning the turf. Continue to water for at least 30 minutes.

If your soil has a high percentage of clay or is very compacted, a fast-release fertilizer is preferred over slow-release. The fast-release formula means it won't remain undissolved on the surface and washed off into the groundwater. If you have sandy soil, you should look for a slow-release fertilizer, preventing it from leaching through the soil too quickly.

If weeds are a problem, you may want to take care of them a few weeks before beginning your fertilizing program. Ortho Weed B Gon for Lawns starts working immediately and kills over 250 broadleaf weeds. If crabgrass control is needed, Ortho has several formulas for controlling it. Remember that the best defense against weeds is a healthy lawn.

Shrubs and Trees in your Lawn

If your trees and shrubs are healthy, most likely they will not require yearly fall fertilization. If growth is poor, first make sure the problems are not a result of insect damage, disease or inhospitable weather (such as drought or heavy frost). Fertilize only when the trees are dormant, in late fall. If you fertilize too soon, the nutrients will stimulate early growth that will damage the trees and shrubs in winter. Use the proper fertilizer mix as specified by your soil test.

Add nutrients naturally with leaves and lawn trimmings

Allowing fallen leaves to accumulate on your lawn is not a good idea. They can harbor diseases by keeping the soil wet and blocking out the sunlight. However, small amounts of leaves, finely shredded by the mower decompose quickly, creating organic nutrients that feed the lawn. Grass clippings are always helpful when left on the lawn.

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