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How to Use Compost

Illustration of compost being added to a potted plant container 

FINISHED COMPOST

Finished compost should look like dark, crumbly topsoil and not like the original materials. Compost should have a pleasant, earthy smell to it. Using “unfinished” or immature material that contains food scraps can attract pests and can cause harm to young plants, so make sure your compost has fully decomposed before adding it to your garden beds.

HOW TO TELL IF YOUR COMPOST IS FINISHED

The simplest way to tell if your compost is mature and ready to use is by doing the “bag test.” Put a handful of moist compost into a zip-lock bag and press out the air before sealing. Leave it for three days, then open the bag. If you detect an ammonia or sour odor, the microorganisms are still at work and you need to let your compost finish curing. Test another sample of compost again in a week.

USING FINISHED COMPOST

There are various ways to use your finished compost. You can sprinkle compost on top or mix it into your flower and vegetable beds, gently rake compost into tree beds, blend it with potting soil to revitalize indoor plants, or spread it on top of the soil on your lawn as a soil amendment.

COMPOST IN THE HOME GARDEN

Adding compost to your garden helps improve the structure and overall health of your soil. Compost will help the soil retain moisture and will increase your overall earthworm and microbial population, which serve as biological controls against unwanted pests. In addition, compost will provide a slow release of macronutrients, which means that your plantings will get a steady supply of nutrients as needed.

Usage

What To Do

Amending Soil Work 1 - 2 inches of compost into the top 3 - 5 inches of soil.
Growing Vegetables

 

Give your vegetable garden plenty of compost in the fall. Spread several inches of compost on top of the existing bed, then till it into the soil in springtime.
 
Put a handful of compost in each hole when you are planting.
 
Once plants begin to grow quickly, you can add a half-inch layer of compost around the base of the plants. Provide "heavy-feeder" plants such as tomatoes, corn and squash with 1/2 inch of compost monthly - this will result in great produce!
Growing Flowers In spring, loosen the top few inches of annual and perennial beds and mix in a 1-inch layer of compost. Or in the fall, apply a 1-inch layer of compost as a mulch to protect plant roots from freezing and preserve moisture.
Replenishing Soil in Potted Plants and Window Boxes Even the best potting soil gets depleted of its nutrients as plants grow. To replenish nutrients, add an inch of compost to potted plants and window boxes twice a year. 
 
Or make your own potting soil using two parts screened compost to one part sand or perlite.

 

USING COMPOST FOR GARDENING PROJECTS

Usage

What To Do

Rejuvenating Lawn or Turf When establishing new turf, incorporate up to 3 inches of compost into the existing soil base. If possible, till to a depth of 5 to 8 inches before seeding. Otherwise, seed directly over the compost.
 
On existing turf, you can treat bald spots by incorporating an inch of compost into the soil and then reseeding. This will help with compaction and suppress soil-borne diseases.
 
You can also topdress existing turf with as much as 1/2 inch finely screened compost. This is easiest with a spreader, but you can use a shovel for small areas where you want to add compost. Rake the compost evenly through the grass area to enable the compost to readily sift down into the soil. The compost will sift down into the soil, improving its structure and providing nutrients. Over time, this will mean less compaction, fewer bald spots, and a reduced need for synthetic fertilizers.
Tree and Shrub Planting and Maintenance (Including NYC Street Trees) Picture demonstrating the concept of a dripline When planting a new tree, it is best to work 1/2 - 1 inch of compost into thee top 2 inches of soil from the trunk of the tree out to the dripline. - the outermost parameter of the tree's canopy.
 
Compost used in this way serves as a substitute for the layer of organic matter that naturally exists on the forest floor: it provides organic nutrients, reduces moisture loss, and keeps the soil cool.
 
Don't add compost to a freshly dug hole when planting a tree, as applying compost in this way will discourage tree roots from growing beyond the hole. 
 
Apply compost as mulch to trees and shrubs to prevent weeds and to make plants more drought resistant. Spread up to 2 inches of compost under the tree or shrub out to the drip line (the outermost leaves on a tree) or the edge of the bed. This will help reduce moisture loss and stabilize soil temperature. 
 
You can also incorporate compost into the soil once or twice a year to provide organic nutrients. Before adding compost to compacted soils, gently cultivate the soil with a hand tool; this will prevent damage to shallow feeder roots while making nutrients more readily accessible to the trees or shrubs.
 
Do not place compost or mulch directly against the bark of the tree or shrub or on exposed woody roots as this could cause rot and invite pests and disease.
Maintaining Perennial & Annual Beds Sketch of plants growing in a bed Spread 1 - 2 inches of compost on top of perennial and annual beds in the early spring or fall to prevent weeds from establishing and to make plants more drought-resistant.

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Related Guides

About the NYC Compost Project funded by NYC Sanitation

The Department of Sanitation (DSNY) encourages residents to compost yard trimmings and food scraps in their own backyards and community gardens. This kind of composting is not only the least expensive way to manage organic waste, it also recycles nutrients close to where they can best be used to nourish our city’s soils.

The NYC Compost Project, created by DSNY in 1993, works to rebuild NYC’s soils by providing New Yorkers with the knowledge, skills, and opportunities they need to make and use compost locally. NYC Compost Project programs are implemented by DSNY-funded teams at seven host organizations, including Brooklyn Botanic Garden, Big Reuse, Earth Matter NY, Lower East Side Ecology Center, Queens Botanical Garden, Snug Harbor Cultural Center & Botanical Garden, and The New York Botanical Garden.

If you are interested in composting at home or in your community, the NYC Compost Project provides technical guidance on constructing composting systems and sells low-cost composting equipment. Each site also manages a compost help line to answer questions and to troubleshoot problems over the phone or by email.

NYC Compost Project -- Useful Links

compost project logo