Is Compost Enough For My Lawn?

Some organic lawn care proponents and even some organic lawn service companies feel that all your lawn needs is compost and compost tea. Are they right?

I don't think anyone that is into organic gardening or organic lawn care dismiss the benefits of compost but is only using compost enough to get the best lawn you can? Well I'm not an expert on compost who has performed decades of research on compost but Abigail A. Maynard, PhD. of the Connecticut Agriculture Experiment Station is.

In 2000 Dr Maynard published a bulletin titled "Compost: The Process and Research" which is something everyone should read that wants to compost at home. It will tell you practically everything you need to know about making compost, leaf mold and using composted manure and municipal solid waste (stuff like Milorganite.)

The research was on vegetable gardens and crops which is not the same as topdressing your lawn with compost, however it is still important to read and I'll address some of the applications to turf along with links to other research specifically related to applying compost to lawns. The summary of Dr. Maynard's bulletin is below.

Using compost in the garden has many benefits. For most vegetables and cut flowers, recent research at The Connecticut Agricultural Experiment Station has shown that fertilizer can often be eliminated when the soil is amended annually with 1 inch of leaf compost. However, optimum yields are obtained when leaf compost and some inorganic fertilizer are used, usually half the normal rate, and after 2 or 3 years of consecutive compost amendments. Optimum yields can also be achieved using compost and organic fertilizers but they are generally less effective, especially on sandy soils. For vegetables that demand higher amounts of nitrogen, a cover crop incorporated into the soil in addition to the leaf compost amendment may be necessary for optimum yields. Compost is most effective when applied in the spring before planting. For optimum results, leaf compost may be applied every year, especially in sandy soils, and can also be safely applied at higher rates if compost is available.

When using a manure based compost with a higher nitrogen content, application may be limited to 1-inch in three consecutive years to avoid nitrate leaching. Yields will not decrease if no compost is applied every fourth year. Application rates of greater than 1-inch with a manure based compost is not necessary and may cause excess nitrate to leach to the underlying ground water, especially in sandy soils.

As compost increases the water holding capacity of the soil, compost-amended soils take longer to warm in the spring. If the spring is cool and wet, early crops, such as peas and radishes, can have reduced yields on compost-amended soils because germination is delayed and the seeds eventually rot. Plant density can be improved by either treating the seeds with a fungicide or seeding at a heavier rate to compensate for seeds that rot.

Undecomposed leaves can also be used as a soil amendment. While there is usually no significant improvement in yields as compared to compost applications, there are virtually no detriments to soil or plants if undecomposed leaves are applied the previous fall. An application of 100% oak leaves or 100% maple leaves shows no adverse effects to soil or plants. A beneficial effect occurs as organic matter of the soil increases slowly if yearly applications occur.

Two inches of compost applied as a mulch are effective for weed control. While not completely eliminated, weeds will be reduced to numbers that can easily be controlled by hand. Control, however, is limited to 1 year.

So in Dr. Maynard's research, she found that adding compost can be used to replace fertilizer but you'll get better results if you still apply fertilizer, even organic fertilizer in addition to compost. Also, you have to keep in mind that they were applying 1" of compost and tilling it into the soil. That's very different than the 1/4" to 1/3" of compost that is used to topdress lawns.

There is a reference in this feasibility study that mentions compost can be used to reduce fertilizer input in turf down to 30% but I can't find the reference. It seems to be from an interview and not directly from a study. Other research I have read indicates that golf courses topdressed monthly with compost can reduce lawn diseases.

Much of the compost in many areas is generated as the result of landfill restrictions on yard waste, mainly fall leaves. Municipalities are either required, or in some cases prefer to collect leaves and recycle them into compost rather than pay to send them to a landfill. Leaf compost is not very effective as a fertilizer. Composted manure provides extra nutrient value but may not be readily available.

One benefit of compost is the introduction or greater colonization of mycorrhizae which are a fungus that attach to the roots of plants, including grass, which helps them absorb available nutrients. You still need to have the nutrients in the soil and using just compost may not be enough.

My opinion after doing reviewing some of the available research is that compost is a great amendment to your lawn but unless you topdress multiple times a year and mulch your grass clippings back into the lawn you will still need to supplement with fertilizers, preferably organic. Even if your grass looks good with just compost and compost teas, it will likely look even better with the addition of supplemental organic fertilizer.

There are some drawbacks to compost topdressing as well. First, it can be expensive. You'll need 1 cubic yard of compost to topdress 1,000 sq ft of lawn to a depth of 1/3". Most people will need to have the compost delivered which can run around $50 per cubic yard. Many bulk compost dealers also have minimums for delivery. You can rent a pick up for the day but that will also run you about $50. You can make your own compost inexpensively but most people don't have the space or material to make the amount of compost they'll need.

Spreading compost is also not as easy as spreading fertilizer. Most DIY'ers dump their compost in piles then use a rake to spread it around. Commercial lawn care services use expensive topdressers to quickly and consistently apply compost. Something like the Spyker model 288 Spreader could be used if the compost is fine enough. This might require you to screen it yourself if you can't find good screened compost. The compost should also not be too wet. You'll probably need to refill the hopper about a dozen times to cover 1,000 sq ft. It's a good commercial grade spreader that you can use for spreading other materials. It is commercial grade and will last a long time but it is very expensive compared to the spreaders most homeowners use.

Top dressing with compost can also be messy and can be tracked into your home easily until it starts to work in and gets consumed by your microherd. It can also leave the lawn looking dirty until it's watered in or brushed clean. Composted manure that hasn't fully decomposed can smell.

The studies also seem to indicate that you can't just go from a synthetic lawn care program to just using compost. It may take a few years for your soil to adjust. Even if you didn't do anything to your lawn in the past, the effects of using only compost may take years to see fully.

Topdressing with compost once or twice a year will help your lawn in many ways. but in many cases it doesn't seem like it will be enough or practical.