To Do List: Fall or Early Spring
The easiest way to start the move towards organic lawn care is to make sure your lawn is really healthy. All of the regular seasonal lawn maintenance chores are therefore excellent ways to go. Those chores are summarized here.
Remove Thatch Thatch is that layer of stems, roots and dead organic matter you can see when you part grass stems. A thick layer of thatch suggests overuse of synthetic pesticides or fertilizers, since these tend to kill off the micro-organisms that help organic matter to decompose.
Thatch only becomes a real problem when the layer is thicker than a half inch, at which point it can become a breeding ground for insects and for various fungi, and a barrier in the way of water absorption. If you scroll through a page on fighting lawn problems, again and again you will see advice to remove excess thatch.
Clippings often get blamed for thatch, and people rake clippings because they don't want to contribute to thatch build-up, but this is a false problem with a non-solution. Clippings only contribute to thatch if they are excessively long or if the thatch layer is so deep that it keeps clippings from decomposing.
Even a thin layer of thatch should be broken up or removed every couple of years, to prevent it from building up past that point. For everyday thatch of less than half an inch in depth, use a garden rake or a tool designed for removing the matted material. Top-dressing (adding a thin layer of something on top, rather than digging it in) with soil or compost can also be helpful, as both these materials contain microorganisms that will help the thatch to decay. For regular seasonal maintenance, these are all that should be necessary, and on many lawns they may only be necessary once a year or even less. Just check the thatch level each spring and fall.
For more serious thatch buildup, you may need to rent a vertical mower, a specialized machine that works vertically to break up and remove buildup.
Unfortunately, a vertical mower can be so hard on the rest of your lawn that you'll often need to reseed after using one. Anything that hard on the lawn should only be used in spring or fall, when grass recovers more quickly than it can in the heat and stress of summer. Spring and fall are also the best times for overseeding, of course.
An alternative approach is to remove as much thatch as you can manually, then aerate like crazy and top-dress generously with compost. Aerating breaks up some of the thatch, while compost adds micro-organisms that help decompose what's left. If you do this in spring and fall, you may well be able to bring even a thick layer of thatch under control without resorting to a vertical mower.
Aerate Aerating removes plugs of soil, which helps reduce soil compaction, one of the most frequent problems of older North American lawns. It also opens the soil to fertilizer, amendments, and seeds, so it is an excellent preparation for other seasonal care.
You can buy a home lawn aerator tool, rent a bigger, mechanized version, or hire out the job. It's important to cover the lawn several times in more than one direction, so that it gets thoroughly and evenly aerated.
Amend Soil Soil amendments actually improve the soil's ability to supply nutrients, water, and air to plant roots. The movement or availability of these three essentials can be inhibited by compaction, high clay or sand content, and high or low pH. All of these are soil conditions independent of nutritional content, but they have a direct bearing on whether nutrients can be taken up by a plant.
Many amendments do supply nutrients, but their primary purpose is to improve soil texture and structure.
Spring and fall are the ideal times to apply soil amendments, but lighter doses can be put on even in mid-summer. Before you start adding lime or sulfur, however, test your soil pH (or have it done) so you're sure to be adding the right thing.
Here's a quick and dirty overview of amendments. The knock-down drag-out version is under our Guide to a Healthy Lawn.
Compost: If you're not sure what your problem is, add compost. For that matter, even if you are sure, add compost. Compost is the miracle amendment, for it improves all soils. It helps balance pH, making acidic soils more alkaline and alkaline ones more acidic. It improves soil retention in sandy soils and drainage in clay soils. Used regularly, it helps reduce compaction. It contains micro-organisms which help organic matter decay, keeping thatch under control and ensuring that clippings will in fact disappear, and not lie around in an unsightly fashion.
For Sandy Soils: Organic additions work best to improve drainage and relieve compaction in sandy soils, because organic matter derived from plants and animals holds many times its own weight in water. Compost adds much more than organic matter, being rich in nutrients and micro-organisms, but for sheer unadulterated water retention, peat and sphagnum moss or coconut fiber cannot be beat. Mature, composted manures -- not fresh manure! -- are also excellent.
For Clay Soils: Surprisingly, everything said about sandy soils goes for heavy clay soils as well: organic additions will make the greatest difference. Sand and gypsum are frequently suggested as amendments for clay soils, but many experts question their effectiveness, and they need to be used carefully. (For more on these debates, see Soil Amendments on this site.) With products derived from plants and animals, you cannot go wrong.
To Raise pH (make acidic soils more alkaline): Add lime, which is available in a number of forms. For lime to be effective, two requirements must be met: it must be dampened; and it must be in direct contact with the soil. The necessary chemical reactions cannot take place without water, and because lime is not especially water-soluble, it will not be carried by water into the soil.
Pelletized lime is the easiest to handle and to apply, but not the cheapest, as it is a refinement of one of the simplest mined forms. Those forms are calcitic lime, which will also add calcium, and dolomitic lime, which will provide both calcium and magnesium. Both are sold as very fine powders, like all lime save the pelletized.
Other forms of lime -- marl, hydrated lime (slaked lime) and burned lime (quick lime) are not good options for lawns: the first contains various impurities, while the others are so highly concentrated that they can be dangerous to handle and will burn established lawns.
To lower pH (make alkaline soils more acidic) Add sulfur, which, like lime, comes in several forms. For ground rock sulfur, add 1.2 ounces per square yard to sandy soils, and 3.6 ounces per square yard for any other soil.
A number of organic (plant-derived) products will also lower pH, among them peat moss, organic cottonseed meal, and even animal manures, but none of these works as effectively as sulfur.
Fertilize Spring and fall are the ideal times for fertilizing, especially in the north. Summer fertilizing is less of an issue in the south, where warm-season grasses that continue growing all summer are the norm, but in the north, most lawns have cool season grasses that go dormant during hot weather. Over-stimulating them during this phase just leads to problems, so go lightly.
For quick results, use fish emulsion, a quick-release, organic, nitrogen-rich fertilizer that can be sprayed or sprinkled. DON'T APPLY FERTILIZER AT MID DAY, and DON'T USE MORE THAN IS RECOMMENDED, especially in hot, sunny weather; that "cure" will definitely be worse than the disease, as nitrogen + sun = burned grass. Quick-release fertilizers don't last long, so give your grass another dose a couple of weeks later.
For summer-long results, use a slow-release fertilizer such as organic cottonseed meal, corn gluten or blood meal in autumn and again the following spring (see Organic vs. Synthetic Fertilizers).
WARNING: Don't use corn meal within several months of reseeding your grass, as it also kills seeds.
Overseed This term refers to seeding over an existing lawn. It's a great way either to fill in bare spots or to gradually change your grass type.
If you've got a standard-issue lawn, chances are the grass itself is not one best-suited to the region where you live, which makes all lawn care a challenge, organic or not. Overseeding lets you add a better-suited grass to your lawn without requiring that you start over from scratch.
Mow your grass as short as your mower will let you. This will give the seeds better access to the soil below and more light once they sprout. It will also stress the old grass a bit, giving the new type a fighting chance to establish itself.
Remove thatch if you've got a thick layer. For seeds to take root in soil, they must touch it. A thick layer of thatch can be a major obstacle to successful overseeding, so if you've got one, you're going to need to get rid of it.
Aerate to improve soil structure and to give seeds a better chance of rooting in soil.
Often, a brisk raking will loosen thatch and soil sufficiently. This may be all you need to do after mowing.
A number of different sources recommend seeding much more thickly (up to one and a-half times as thickly) as recommended for whatever seed you're using. This is particularly good advice if you're trying to replace one type of grass with another. The undesired grass already has a serious head start, and over-seeding (seeding too much) can help to correct that discrepancy. Using a slice-seeder will ensure that seed is deposited into soil at the correct rate.
For best results, topdress by sprinkling compost, topsoil, peat moss or coconut fiber over the newly seeded lawn, then water until the soil surface is dampened everywhere. The soil amendments will give the seeds a boost, and will help retain water over and around the seeds.
If you don't topdress, rake the ground lightly to bring seeds into better contact with soil, then water.
Keep the soil surface damp while seeds are germinating and while seedlings are young and new. This probably means twice-daily watering on days without rain.