Learn / Composting methods
Pit composting: a water-saving method for dry weather.
In pit composting you build your compost in a hole in the ground instead of in a heap above it. The soil walls hold moisture, so a pit suits dry seasons, dry areas and farms where water is scarce. It does not suit wet weather or sites where water can flow in.
The numbers that matter
A pit is a heap turned upside down. The same rules apply: a mix of dry and green material, enough moisture, and some air. What changes is where water goes, and that decides when a pit is the right choice.
When a pit works, and when it doesn’t
| Pit | Heap above ground | |
|---|---|---|
| Best season | Dry season, or just after the rains. | Rainy season and wet areas. |
| Water | Loses less moisture, so it needs less water. | Dries faster in sun and wind unless covered. |
| Risk | Rain or flood water runs in, and the bottom rots. | Rain can leach nutrients unless the heap is covered. |
| Labour | Digging at the start; lifting material in and out when turning. | No digging; easier to turn. |
| Monitoring | Checked with a stick pushed through the cover. | Checked by thermometer or by hand. |
Do not use a pit if:
water can enter it, the site can flood, or the rains are on. In wet conditions a pit holds water and air is cut off, which causes rot, bad smell and loss of nitrogen as ammonia. Build a heap instead.
SOURCES: SUE EDWARDS AND HAILU ARAYA, “HOW TO MAKE AND USE COMPOST” (FAO, 2011); THE STANDARD (KENYA), “HOW I PREPARE MY COMPOST MANURE”
Siting and sizing the pit
- High, well-drained ground. Pick a spot where flood water cannot reach and that drains well. Check that water does not seep into the hole before you fill it.
- Near water and the work. A site close to a water source or the compound keeps the carrying down.
- No deeper than 1 m. Below that the pit is cold and microbes run short of oxygen.
- Wide enough. The FAO guide gives about 1 to 1.5 m wide and 1 to 1.5 m long for the Indore pit, and 1 to 2 m by 1 to 2 m for the Bangalore pit. Make a pit longer rather than wider or deeper. Small pits dry out quickly and make poor compost.
- Seal the walls. Plaster the bottom and sides with a slurry of dung and water, or topsoil and water if you have no dung.
- Mark it. Ring it with stones or a small fence so people and animals don’t fall in or break the cover.
Some Kenyan farmers dig deeper. One farmer described in The Standard uses pits 1.5 m deep, 1.5 m wide and 1 to 2 m long. The FAO guide advises staying within 1 m. If you go deeper, expect the bottom to compost more slowly, and keep your layers loose.
SOURCES: FAO, “HOW TO MAKE AND USE COMPOST” (2011); THE STANDARD (KENYA), “HOW I PREPARE MY COMPOST MANURE”
Layer by layer
This is the layered pit method (Indore) described in the FAO guide. Cut or chop all plant material to 10 to 15 cm lengths first.
- FoundationLay 20 to 25 cm of dry plant material, such as stalks and straw. Dampen it so it is moist but not wet.
- Dry layer with helpersAdd 20 to 25 cm of dry material mixed with soil, manure or ash. Keep it moist but not soaked.
- Green layerAdd 20 to 25 cm of fresh green material. Do not sprinkle water on this layer, since it already holds moisture.
- Manure layerSpread 5 to 10 cm of animal manure, or a 1 to 2 cm layer of manure slurry. You can leave it out if you have no manure.
- Repeat and domeRepeat the layers until the pit is full. Build the middle 30 to 50 cm higher than the sides so it forms a dome and sheds water.
- Add a testing stickPush a solid stick down through the middle so the top sticks out. You will use it to check heat and moisture.
- CoverSeal the top with wet mud mixed with grass or dung, wide leaves, or plastic. This keeps rain out and moisture in. Cover the top with branches so animals and people don’t break it.
Smaller loads.
The FAO guide also describes a Bangalore variation, where you fill the pit in weekly additions rather than all at once. It suits households with limited labour.
SOURCE: FAO, “HOW TO MAKE AND USE COMPOST” (2011)
Testing, turning and timing
You cannot see into a sealed pit, so use the stick.
| Pull out the stick and… | It means | What to do |
|---|---|---|
| It is cool, with little smell | Too dry. | Add water, or diluted urine. |
| It is warm or hot, with an ammonia smell | Too wet, or too much nitrogen. | Mix in dry material. |
| It is warm and smells earthy | Working well. | Leave it. |
Test one week after covering the pit, then every one to two weeks until the compost is mature. The “earthy” row is our plain-language summary, not a quote from the source.
When to turn
- Warm climate: turn about one month after filling. In a cold climate wait two months or more.
- Only turn if you have water. Turning dries the material, so do it only when you have enough water or urine to re-moisten it.
- Ready in: about 3 to 4 months in a warm climate. In colder places it can take 6 months to a year.
The three-pit system
If you have the space, dig three pits side by side. About once a month, move the contents of pit A to pit B, and then B to C. Pit C holds the mature compost. You can use compost about 4 months after filling the first pit, and pit A is then free to fill again.
SOURCE: FAO, “HOW TO MAKE AND USE COMPOST” (2011)
Two pits and a heap, on one farm
A farmer profiled in The Standard makes compost with two pits and a finishing heap.
- Weeks 1 and 2Collect animal waste in the first pit.
- Week 3Mix plant residues and animal waste thoroughly in the second pit, adding water to ease mixing.
- About a monthLet it decompose in the second pit.
- FinishMove it to a heap and dry it for about two weeks, depending on the weather.
She chops plant material small, uses only weeds that have not set seed, and turns the compost regularly. By her own account she makes about 2 tonnes every two months, spends about Sh600 on labour, and saves about Sh18,000 per season compared with the roughly Sh22,000 she would spend on fertiliser.
These are one farmer’s figures as reported by the newspaper. Your savings will depend on your labour, materials and the fertiliser you replace.
SOURCE: THE STANDARD (KENYA), “HOW I PREPARE MY COMPOST MANURE”
What to look for and how to fix it
| What you see or smell | What it means | What to do |
|---|---|---|
| Rotten smell, water at the bottom | Water is getting in, or the pit is too wet and short of air. | Divert surface water away. Turn the contents with dry coarse material, or move them to a heap above ground. |
| Ammonia smell | Too wet, or too much manure. | Mix in dry material. |
| Dry, cool, little change | Too dry, or the pit is too small. | Add water or diluted urine. Next time dig a longer pit. |
| Cold, slow bottom layer | The pit is too deep. | Turn it so the bottom moves to the top. Keep future pits within 1 m. |
| Cover broken or collapsed | People or animals stepped on it, or rain got in. | Repair the seal and rebuild the marking. |
One caution of our own: a pit is hard to check for the high temperatures that kill pathogens and weed seeds. If your pit contains manure and the compost is going on vegetables, turn it, let it cure fully, and consider finishing it in a heap where you can measure the heat.
SOURCES: FAO, “HOW TO MAKE AND USE COMPOST” (2011); THE STANDARD (KENYA)
Questions people ask
Is a pit better than a heap?
Not always. A pit wins where water is short and the weather is dry. A heap wins in wet weather and where you want to measure heat.
How deep should I dig?
No more than 1 m, according to the FAO guide. Some farmers dig to 1.5 m, but the bottom then composts more slowly.
Do I need manure?
No. The manure layer can be left out if you have none, though manure helps the pile start.
Can I use a pit in the rainy season?
It is best avoided. Rain that runs in leaves the pit wet and short of air, and the compost rots.
How do I know it’s ready?
Mature compost in a warm climate takes about 3 to 4 months. It should look dark and crumbly and smell earthy, and it should no longer heat up when turned.
Is an open pit dangerous?
An uncovered pit is a fall risk for children and animals. Keep it covered and marked, as the guide advises.
Not sure which method suits your land?
We train farmers and groups to choose and run the right composting method for their site, water and materials.