Knowing when to fertilize your lawn can be challenging and not always as easy as following the instructions on a bag of fertilizer. The natural growth cycle of the lawn dictates specific times to fertilize. If fertilizer is applied at the wrong time, it can weaken or damage the plant, resulting in the opposite of the desired effect. Here's a season-by-season rundown of when to fertilize your lawn.
Contrary to popular belief, the lawn does not need to be fertilized at the first sign of nice weather in the spring. If a solid lawn care regimen is in place, there will be enough carbohydrate reserves in the grass (from the slow-release fertilizer you applied in previous fall) to last through most of the spring. The carbohydrate reserves in the roots begin to decline in late spring, and this is when you should first apply fertilizer for the growing season ahead.
A lawn will use its late-spring feeding to restore its carbohydrate reserves so it can get through the ups and downs of summer. Drought, heat, frequent mowing and other stresses can bring a lawn to its knees. By late summer it's ready for another application of fertilizer. Not a lot; just enough to get it through fall. The late-summer application is considered a bridge feeding to get the lawn through the fall.
By late fall it's time to start thinking about the next season.
A substantial, late-season fertilizer application will help maintain some green color in the winter and create a quick green-up in the spring. The late fall application is important so that the lawn has help in the spring but not so much that it interferes with its natural growth cycle. The goal of this feeding is to nourish the lawn for its winter hibernation, not to make it nice and green over the cold months.
Although not fertilizer, lime is often applied seasonally to adjust pH levels in the soil. A soil test will is the best way to know whether your lawn needs lime (and how much it needs). Although there is not a specific time that is best for applying lime, it is most commonly done in fall, before the ground freezes. Fall is also the best time to aerate a lawn, and applying lime after aerating helps the treatment get into the soil.
Get Local Advice
Growth cycles of turf vary from climate to climate, as does the behavior of various grass types. If you're just following the recommendations on your package of fertilizer, you're getting very generic advice. A better source for tips on lawn care — and indeed all plant care — is a local extension service. Most universities have an extension that offers free advice online or through a phone-in hotline. The advantage of an extension is that its experts understand how to care for plants in your climate, something a national producer of fertilizer cannot do.