Last Call for Lawn Fertilizer!

Mid-November is here, and that means we have one last chance to feed our lawns before the soil freezes or gets covered in snow. Late fall fertilizer applications, when done correctly, promote plant health by providing important nutrients when your grass is looking for them before going dormant. A late fall fertilizer application ensures that your grass has the energy it needs to heal from the stress it encountered and come back strong in the spring.

The three main nutrients in most lawn fertilizers are nitrogen, phosphorus, and potassium. Generally, lawns in eastern Washington need nitrogen, whereas lawns in western Washington need phosphorus and potassium. Ideal fertilizer mixes for western Washington are 21-7-14, 15-5-10, and 12-4-8. These numbers give the percentage by weight of nitrogen, phosphorus, and potassium, respectively, in the fertilizer mix. Sulfur, another nutrient commonly found in mixed fertilizers, can give a lawn richer color and control certain weeds and diseases.

Before buying any fertilizer and applying it, you need to understand what nutrients your lawn lacks. The best way to learn this is by performing a soil test. Most lawn and garden stores provide do-it-yourself rapid soil tests to give you a good idea what fertilizer mix is best for you. Once you know the nutrients needed, determine whether slow-release or quick-release is best for your individual lawn. Inorganic forms of quick-release fertilizer should perform well in late-fall. A couple caveats to that are if your lawn is very sandy and/or sloped or if your lawn is close to a vulnerable water body. In these cases a slow-release fertilizer or applying quick-release in lower quantities may be the best option. 

If you're planning on using a granular fertilizer, a drop type fertilizer spreader works best, and a broadcast type fertilizer spreader is ideal for pelleted forms. In Washington, 4 lbs of nitrogen per 1,000 square feet of lawn applied once a year is usually sufficient. Spread that out over four separate applications. So, use 1 lbs per 1,000 square feet of lawn this fall. Less sulfur is required, with two applications throughout the year adding up to 2 to 3 lbs per 1,000 square feet total.

The timing of your fertilizer application is important because it can impact how well it is taken up by the grass in your lawn as well as how much is lost to the environment. Apply too early and the grass might get hungry for nutrients again or fall rains could wash it away. Applying fertilizer before the ground freezes and after the majority of fall rains ensures it gets used by the grass as efficiently as possible. Try to apply your fertilizer when there is no rain in the immediate forecast as well. This gives the nutrients time to breakdown, absorb, and stay put, limiting any environmental issues. The latest fall fertilizer should be applied in Washington is December 7.

To learn more about fertilizing your lawn, check out our Lawn Care Playbook! It's full of information and references from WSU and others that you can apply to help your lawn reach its maximum potential.

References: WSU. 2015. Home Lawns.

WSU Soil Temperature Overview