Composting basics

Step by step

1. Step 1

   Site your compost pile more than 6 ft (1.8 m) from your house or other wooden structures

   Build or use a bin at least 3 cu ft (0.08 cu m), about 3 ft wide, deep, and tall, and keep it under roughly 5 cu ft, or use a pile of at least one cubic yard (0.76 cu m). You can also build a freestanding pile 3 to 5 ft (0.9-1.5 m) high and at least 3 ft (0.9 m) across. A pile under 3 cu ft (0.08 cu m) often struggles to hold heat, especially in late fall and early winter.

2. Step 2

   Balance your materials at about 25 to 30 parts carbon-rich brown material to 1 part nitrogen-rich green material, or a 2:1 ratio of browns to greens by volume

   If you don't have enough green material, mix in a high-nitrogen lawn fertilizer without herbicide, at one-third to one-half cup per 25 sq ft (2.3 sq m) of surface area. You can also use a 2-in (5 cm) layer of livestock manure as your nitrogen source.

3. Step 3

   Chop or shred materials into pieces smaller than about 2 in (5 cm) across so they break down faster

   Grind up any branches or twigs thicker than 1 in (2.5 cm) in diameter before you add them. Shred leaves down to about 6 in (15 cm) or smaller. If you want to compost shrub trimmings, chop them to less than one-fourth in (0.6 cm) across.

4. Step 4

   Build the pile in layers of 4 to 5 in (10-13 cm) of browns, then 2 to 3 in (5-8 cm) of greens, repeating this up the pile

   You can instead start with 8 to 10 in (20-25 cm) of leaves, grass, or plant trimmings and stop layering once the pile reaches about 5 ft (1.5 m) tall. Another option is a 6-in (15 cm) layer of brown material, then 2 in (5 cm) of green material, then 2 in (5 cm) of soil, repeated up the pile. Or build alternating 3- to 4-in (8-10 cm) tiers up to a height of about 3 ft (0.9 m).

5. Step 5

   Moisten the materials to about 40% to 60% moisture, roughly the feel of a wrung-out sponge

   Keep the pile damp but not soggy throughout, like a wrung-out sponge or damp rag. A pile that is too wet may not have enough oxygen for its decomposers, and breaking down without oxygen can produce compounds that are toxic to some plants. If the pile dries out, add water and turn it so every bit of material gets coated, then cover it loosely with a tarp or landscape fabric.

6. Step 6

   Turn the pile about once a week, moving material from the outside toward the center

   A pile that is never turned can take three to four times longer to produce usable compost than one turned weekly. You can instead turn it often for the first 3 to 4 weeks, then just once or twice during the rest of composting. After 4 to 7 days the pile cools and should be turned again at that point. If it isn't heating up, make it bigger, add water while turning, or mix in nitrogen-rich material. If it's decomposing slowly because of too much brown material, add one pound (0.45 kg) of urea per cubic yard (0.76 cu m).

7. Step 7

   Check the pile's internal temperature at least 12 in (30 cm) below the surface, using a thermometer that reads up to 160°F (71°C) or higher

   Monitor it once or twice a week, and turn the pile when the temperature is dropping or holds at 80°F (27°C) for a few days. Keep it between 140°F and 160°F (60-71°C), or by another measure between 130°F and 160°F (54-71°C), for active composting. Temperatures need to pass 130°F (54°C) to kill most pathogens and 140°F (60°C) to destroy most weed seeds. If the pile climbs to 160°F (71°C) it can kill the decomposer organisms, and many of them go inactive or die above 149°F (65°C). If the pile smells like rancid butter, vinegar, or rotten eggs, turn it and mix in dry browns such as leaves, straw, sawdust, or wood chips.

8. Step 8

   Keep meat, fish, bones, fats, grease, lard, oils, eggs, dairy products, cheese, and salad dressing out of the pile, since fatty foods cause odors and attract animals

   Keep dog or cat feces, used litter, and dirty diapers out too. Leave out black walnut leaves and twigs, since they release substances that can harm plants. Leave out pressure-treated lumber, pressed wood, and plywood scraps, since they contain toxic chemicals. Add only weeds that haven't gone to seed yet, and keep paper to no more than 10% of the pile's total weight. Herbicide residue can persist through composting and harm plants grown later in compost-amended soil. Most guidance advises against adding animal manure to a home pile, so check your local and county codes, since some materials, including raw manure, may be restricted. Nutshells, tree roots, magnolia and oak leaves, and sweetgum balls all decay very slowly.

9. Step 9

   Let the compost cure for 6 to 12 weeks after it stops heating before you use it

   For a seed-starting mix, let it sit for an extra month or two beyond that. Compost is ready once its temperature is less than 10°F (5.6°C) warmer than the air around it, looks dark brown or black, crumbles when squeezed, and smells earthy rather than rotten. Finished compost typically has a pH between 6.5 and 7.0. Screen it through hardware cloth with half-inch (1.3 cm) openings to remove any uncomposted chunks. Mix 1 to 3 in (2.5-8 cm) of compost into the soil surface and work it to a depth of 4 to 6 in (10-15 cm), or use 1 to 2 in (2.5-5 cm) worked into the top 6 to 8 in (15-20 cm) of topsoil. As mulch, spread it 1 to 2 in (2.5-5 cm) thick and reapply once or twice a year.