Homemade compost, even old compost, is mostly organic matter with microbes. Commercial compost will have a higher percentage of soil, but it will still have some organic matter.
Once the temperature of homemade compost starts lowering to air temperature, then curing can begin.
Both homemade and store-bought compost can last for a year or more.
Can You Leave Compost Too Long?
The length of time you leave the compost will depend on certain factors such whether you have the space to store it and if you need the compost for planting asap.
I have two compost bins which I compost most of the kitchen waste/last falls leaves, and leave one to mature while I start the second one. My garden waste compost heaps are left to mature over time - which usually takes about 2 years, depending on the size of the branches etc. Even a small garden can have a few compost piles hidden behind an outbuilding or structure.
- Leaving the compost to mature will result in a higher quality of compost. Humus increases with the length of the maturing process.
- Curing or maturing finished compost can take anywhere from a few weeks to a year or more.
- Immature compost can be harmful to plants.
- During the curing/maturing phase, the compost should not be turned or tumbled.
- The maturing or curing phase is often left out in commercial compost. If you want to know what is in the compost you are purchasing, look for the label STA Certified (The US Composting Council’s Seal of Test Assurance Program). The maturity of the compost is tested, among other tests.
Does Compost Expire?
Compost does not expire, but it loses its nutrients over time and will reduce in size considerably.
If you have left your compost to dry out, add some greens like grass clippings and a little carbon. Turn the compost and sprinkle with water if it has become hard.
The grass clippings will add nitrogen, and the browns (dried leaves, shredded paper, or cardboard) will add carbon. Mix thoroughly and keep it moist.
If your old compost is wet and soggy, either add carbon or spread it out (space permitting) to dry.
Store-bought bagged compost like homemade compost, will degrade over time. Some stores will have it on special offer when their new stock comes in. Although it has not expired, I use it to bulk out my homemade compost or as a mulch.
Can Compost Be Stored For Later Use?
Yes, if your compost is ready and you aren’t, then compost can always and should be stored for later.
Either store it in the bin it was made in or if that bin is required for a new batch of compost, store it in bags or any other old container big enough – old garbage can etc.
I often store my compost in the large chicken feed bags. Make sure it is kept adequately moist, not soggy.
If you plan on storing the compost for a longer time than the next season, let it dry and keep it covered. This will slow or stop the composting process. Revive it when needed with some added, almost complete compost and turn for a few weeks.
Shop bought compost can be stored the same as homemade compost. If the bag is open, try and tie it closed or put a brick on top and keep it away from the rain.
The nutrients will become depleted over time, and then I would suggest using it as mulch or a soil conditioner or adding it to your new unfinished compost.
How Long Can Compost Be Stored?
Compost should not be stored for more than a year or so. If you are planning on storing for longer, keep adding almost finished compost.
Should I Keep My Unused Compost Covered?
Yes, always keep your unused compost covered. Either in a pile and covered with plastic or in a bin or plastic, make sure it is covered and remains moist and not dry.
- Both homemade and store-bought compost can last for a year or so.
- Compost loses nutrients over time.
- Compost that has been left for a long time can be revived and become viable again.
- Compost can be stored for some time.