RODALE NEWS, EMMAUS, PA—If you're looking for the best organic lawn fertilizer, look no further than the grass clippings and fall leaves dotting your backyard. Not only are they free, using them instead of commercial fertilizers that contain synthetic nitrogen and phosphorus could also save marine life in your community's ponds and rivers. A new study offers the first evidence that banning homeowners from using phosphorus-based lawn fertilizers helps bring depleted waterways back to life. The research was published in the most recent issue of Lake and Reservoir Management.
THE DETAILS: Various state and local governments across the country have banned lawn fertilizers containing phosphorus, due to the wildlife-depleting algae blooms those fertilizers feed in nearby waterways. However, the authors note, until now there hasn’t been hard evidence that those bans have any affect, and that may be why more states haven't adopted them.
These authors collected water samples from three areas of the Huron River near Ann Arbor, MI, which prohibited the use of phosphorus-based fertilizers in 2007, at weekly intervals from May to September 2008. They measured phosphorus levels from one location upstream from Ann Arbor, where the ban wouldn't have any affect, and then in two spots downstream, and compared those levels with similar readings that had been taken from 2003 to 2005. The average reduction in total phosphorus levels after the ban went into effect was 31 percent.
WHAT IT MEANS: Swap out your synthetic fertilizers for compost and other kinds of organic lawn fertilizer, and you can enjoy a healthy lawn as well as healthy rivers and streams. In fact, your turf probably doesn't need fertilizers juiced up with phosphorus, anyway. "I've read studies that show 90 percent of American lawns already have enough phosphorus," says Paul Tukey, founder of the Safe Lawns Foundation and author of The Organic Lawn Care Manual (Storey Publishing, 2007). The nutrient exists naturally in most soil, at levels high enough to provide your grass with the amounts it needs, he says.
You'll also cut down on the need for fertilizers if you just keep your lawn healthy, and fall is the perfect time to get started, Tukey says. "If you set your lawn up right in the fall, you don't have to fertilize in the spring."
Keep your lawn healthy next spring by taking care of these lawn maintenance chores now:
• Got milk? Calcium is an often overlooked but very vital nutrient in healthy lawns, says Tukey, because it builds soil quality. You can apply it in the form of gypsum or limestone; if you go with the latter, make sure you get the right kind. "A lot of people put down dolomitic lime, which has too much magnesium," he says, and that can compact soil and that can lead to an overgrowth of weeds. He says to look for "high calcium" limestone that contains less than 20 percent magnesium; the back of the bag will list the nutrients and their percentages.
• Add N and K, but go light on the P. Fertilizers generally contain three nutrients listed on labels as "N-P-K," nitrogen, phosphorus, and potassium. But not all fertilizers for lawns have all three ingredients, so you can find one without phosphorus but heavy on potassium, which builds cell walls and strengthens soil, and nitrogen. Backyard compost is an excellent organic lawn fertilizer that's a good source of both nitrogen and potassium. Corn gluten, soybean meal, and feather meal are good sources of nitrogen. "Compost is best to lay down in fall," Tukey says, "when there's still a little more growth to happen." He suggests raking no more than half an inch into your lawn around the end of September or early October.
• Recycle your clippings. Grass clippings and mulched-up leaves are excellent organic lawn fertilizers, says Tukey, and they continue to feed your lawn even after it goes dormant. Don't just leave the whole leaves on the ground, though, as that could get you a lawn-unfriendly disease called winter-kill. "Get that lawn cleaned up as best you can," says Tukey.
• Mow low come November. One way to keep the leaves feeding your lawn without all the back-breaking raking is to chop them up with your mower and leave them there. You can—and should—continue to mow until mid- to late November (or just before the regular frosts start in your area), Tukey says. The last time you mow for the year, he advises mowing your grass lower than you would in the summer, around 2 to 2.5 inches. "If you leave that tall grass in place and then get a heavy snowfall, that grass will bend over on itself and you could get snow mold," he says. Taller grasses also provide a nice toasty home for field mice and other pests.