When to Use Fertilizers & Pre-emergents

Knowing when to use fertilizers and pre-emergents can help prepare your lawn for its growing season. By improperly applying fertilizer, you can encourage the growth of weeds or dehydrate your yard. Fertilizer application also depends on whether you are growing warm or cool weather grass. Find out what type of grass is in your yard before fertilizing.

Pre-emergents should be applied twice a year to kill off two types of weeds: summer-growing weeds and winter-growing weeds. Generally, you can apply pre-emegents in March and September. You must apply pre-emergents before the growth of weeds, because it will not kill existing weeds. They are designed to prevent the seeds of weeds from germinating; therefore, you should use weed killer on weeds that are already growing on your lawn. Application dates for applying pre-emergents can be different than your fertilizing dates, because you should apply fertilizer after your grass has "greened up" or come out of dormancy. If you apply a fertilizer that is high in nitrogen before it has a chance to grow, you inadvertently provide nutrients for weeds.

Find out how much thatch you have in your lawn. Thatch is a layer of both living and dead organic matter sandwiched between the soil and grass. Excessive amounts of thatch will prevent fertilizer from properly being absorbed into the soil. Take a screwdriver (thatch is difficult to penetrate) and press in through the thatch to the soil. Measure how far down the thatch goes to your soil. If your thatch layer is over half an inch thick, you should remove it from your lawn. To dethatch, rent a mechanical dethatching rake or use a hand rake to pull up the organic material. Dethatching rakes or power rakes are pushed over your lawn. As the blades roll across the grass, they pull up the thatch. You can rent one from most gardening centers. Once you have dethatched your lawn, keep it watered for several days before fertilizing.

Your fertilizing schedule depends on your type of grass and when it comes out of dormancy. When you see signs of life emerge after winter, water your warm-weather grass for a couple of days. Apply a fertilizer high in nitrogen. Decide if you want to use a quick-release or slow-release fertilizer. A quick-release fertilizer will quickly provide nutrients to your grass, but it has to be applied every few weeks. Slow-release fertilizer releases nutrients over 6 to 8 weeks, but the ground must be warm in order to see optimal results. Fertilizer your warm-season grass again in the late summer to have a green expanse until fall. Cool-weather grass should be fertilized in the late fall to keep it green in the winter. Apply the fertilizer once temperatures have dropped to 60 to 70 degrees F.