Why Is My Compost Not Heating Up? 5 Fixes That Work

The short answer

A compost pile that won't heat up usually has too little nitrogen-rich green material, is too dry or too wet, needs air, or is smaller than about 3 by 3 by 3 feet. Fix the most likely problem first: add fresh greens such as grass clippings, water until the pile feels like a wrung-out sponge, and turn it. An active pile should reach 130 to 160°F within a few days.

Push your hand or a compost thermometer about 12 inches into the center of the pile. The center is what matters; the outer few inches of any pile stay close to air temperature.

How hot should a compost pile get?

An active "hot" compost pile usually reaches 130 to 160°F in its center within a few days of building or turning it. At those temperatures, microbes break material down quickly and kill many weed seeds. Above about 160°F, activity can slow down; turning the pile cools it.

1. Not enough greens

Lack of nitrogen is the most common reason a pile stays cool. Microbes need nitrogen to multiply, and a pile of mostly dry leaves, straw or cardboard doesn't have enough.

Mix in fresh greens: grass clippings, vegetable scraps, coffee grounds, or manure from plant-eating animals. A rough working ratio is 2 to 3 parts brown material to 1 part green, by volume. You'll know you overdid it if the pile starts smelling like ammonia; add more browns to fix that.

2. Too dry

A dry pile is the second most common cause, especially in summer or with lots of leaves. Squeeze a handful from the center. It should feel like a wrung-out sponge, with maybe a drop or two of water.

Water while you turn the pile so moisture reaches every layer. Spraying the top only wets the outer inch.

3. Too wet

A soggy pile goes cold and starts to smell sour or rotten because water fills the air spaces microbes need. Turn it and mix in dry browns such as shredded leaves, straw or torn cardboard. Cover the pile during heavy rain.

4. Not enough air

Microbes that make heat need oxygen. A pile that has been sitting for weeks, or that's packed down with wet grass, may run out. Turning it with a pitchfork, every week or two while it's active, brings in fresh air and usually raises the temperature within a day or two.

5. The pile is too small

Piles smaller than about 3 feet on each side lose heat faster than microbes can make it. Combine smaller piles, or wait until you've collected enough material to build a full batch at once. In cold weather, a pile also cools faster; insulating it with bags of leaves around the outside helps.

Symptom	Likely cause	Fix
Cool and dry, smells like nothing	Too dry or not enough greens	Add greens and water while turning
Cool and soggy, sour smell	Too wet, not enough air	Turn and add dry browns
Ammonia smell	Too many greens	Add browns
Warm in center only, then cools	Needs air	Turn every 1 to 2 weeks
Never warms, small heap	Not enough mass	Build to about 3 x 3 x 3 feet

Is a cold compost pile a problem?

No. Cold composting works fine; it simply takes longer, often 6 months to 2 years instead of a few months. The trade-off is that weed seeds and plant diseases may survive, so keep seedy weeds and diseased plants out of a cold pile.

Next step: check moisture with the squeeze test today, then turn the pile and add one wheelbarrow of fresh greens. Check the center temperature again in two days.

Questions people ask

Should I add a compost starter or activator?

Usually not. Garden soil and finished compost already contain the microbes you need. A starter can't fix a pile that is too dry, too wet or short on nitrogen.

Can compost get too hot?

Piles can exceed 160°F, which slows microbes and in very large, dry piles can pose a fire risk. Turning and adding water brings temperature down.

Will compost heat up in winter?

A large, well-balanced pile can stay warm in its core, but small piles usually go dormant until spring. That's normal.

Can I put meat or dairy in a backyard pile?

Most guidance says no for home piles. They attract animals and can smell, and home piles don't reliably stay hot enough to handle them safely.