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Knowing what to do can mean the difference between a lovely yard and a splotchy mess come next spring.
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Understanding the numbers on fertilizer bags is critical for proper fertilization.
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Unnecessary fall nitrogen applications may lead to winter injury in warm-season grasses, such as Zoysia grass, which reveals itself in the spring as dead patches or areas slow to green up.
Photo courtesy of Bert McCarty, Clemson University
Drinking coffee before bedtime tends to keep me up all night. Fertilizer applied in the fall has a similar effect on warm-season lawns. If you keep warm-season grasses awake and growing for too long into the winter, they will be—like me the morning after too little sleep—half-awake and grumpy next spring.
Unfortunately, gardeners can get confused by the abundance of fertilizer products sold as lawn “winterizers” during late summer and fall. The issue is muddled, because we grow two totally different lawn types in South Carolina: cool season and warm season. Some lawns, mostly in the upper piedmont, are tall fescue, a cool-season grass that stays green all winter.
But most S.C. lawns—the majority east of I-85, in fact—are warm-season types that go dormant and turn brown for the winter. These are most commonly Bermuda, zoysia, centipede and Saint Augustine grasses. Because cool- and warm-season grasses grow in opposite seasons, they should be managed in completely opposite ways. Most common lawn winterization products are designed for cool-season lawns. That means using a winterizer on centipede grass is like giving it a shot of caffeine right before bed. Not good.
So, how should you prep a warm-season lawn for winter? Doing nothing may be the best strategy. If you fertilized your lawn during the growing season based on the results of a soil test and used the recommended fertilization schedule for your grass type (see Clemson Extension’s lawn maintenance calendars at clemson.edu/hgic), it probably doesn’t need fall fertilization.
Whatever you do, don’t apply nitrogen-containing fertilizer after Aug. 15 in the Upstate and Sept. 1 on the coast. Nitrogen encourages growth, and, if it’s applied too late in the year, the grass won’t have time to go dormant before damaging cold arrives. The following spring, you’ll see patches, or perhaps a whole lawn, that failed to green up because of cold injury.
Nitrogen can also encourage cool-season weeds to prosper, leading to a weedy winter lawn. Plus, unused nitrogen can find its way into groundwater and streams, causing pollution. Unfortunately, nitrogen is a common ingredient in winterizer fertilizers, because they are mostly designed for cool-season grasses that need nitrogen in the fall.
Potassium is another common ingredient of winterizers. There is sound reasoning behind applying this nutrient in the fall. Potassium does enhance the cold tolerance of turfgrasses, but only if your lawn needs it. Clemson Extension’s soil tests and maintenance schedules account for this need and recommend potassium applications throughout the growing season. If a late-summer soil test indicates a potassium need, apply it without adding nitrogen by using a fertilizer like muriate of potash (0-0-60), potassium sulfate (0-0-50) or an organic source, such as greensand. Don’t use more than your lawn needs; that won’t produce any greater cold tolerance. In fact, excessive rates of potassium fertilizer can cause foliar burn to your lawn and may compete with its uptake of other needed nutrients.
Following a good fertility schedule throughout your lawn’s growing season will ensure that it has what it needs before fall to survive the winter undamaged. Save the nitrogen until after your grass wakes up in the spring.
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What’s in the bag?
Understanding the numbers on fertilizer bags is critical for proper fertilization.
Commonly expressed as N-P-K, these three numbers (e.g., 10-10-10, 16-4-8, 0-0-60) tell us how much of each major plant nutrient—nitrogen (N), phosphorous (P), and potassium or potash (K)—are in each bag of fertilizer as a percentage by weight. This holds true for both conventional and organic fertilizers. A 50-pound bag of 10-10-10 contains 10 percent, or 5 pounds, of each nutrient.
Rarely do plants need equal amounts of these minerals, so soil test results usually recommend imbalanced fertilizers, such as calcium nitrate (15.5-0-0) and muriate of potash (0-0-60). By reading the numbers, you can figure out the best mix of fertilizers to apply.
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Winter weed woes
Bothered by those pesky patches of green weeds in your dormant winter lawn? If so, consider applying a fall weed preventer.
Weed preventers (also known as preemergent herbicides) can be applied when nighttime lows reach 55 to 60 degrees for four consecutive days. They help prevent winter weeds, such as henbit and annual bluegrass, from emerging. Typically the right time is Sept. 1 to 15 in the piedmont and Sept. 15 to Oct. 1 for the midlands and coast.
The effects of weed preventers may wear off after 6 to 12 weeks, depending on temperature and rainfall, so a second application nine weeks after the first will extend control through each season. As with any product, read and follow all label instructions before applying.
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Feeding fescue
Tall fescue is a common lawn grass in the Upstate, which is pretty much as far south as this cool-season grass grows. Fertilizing fescue calls for a different approach than warm-season lawns.
Unlike its warm-season counterparts, fescue stays green year-round, and its growing season is fall through early spring. Although it may remain green, it essentially stops growing during the summer. As a result, fescue lawns should be fertilized with one pound of nitrogen per 1,000 square feet of lawn in September, November and February, and never after March 15.
S. CORY TANNER is an area horticulture agent and Master Gardener coordinator for Clemson Extension based in Greenville County. Contact him here.
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Get More
- How to prevent lawn weeds: Tips and products for keeping the weeds at bay.
- Winning the turf war: Best practices for mowing, fertilizing and watering your lawn.
- Pest control: How to battle the three most destructive pests in S.C. lawns.
- Grasses for South Carolina: Cool- and warm-season grasses that thrive in our state.
- Let it grow: A Carolina Yard lets homeowners enjoy their outdoor spaces with fewer maintenance chores.