Ask a Master Gardener: What to put in the compost
Leaves are the most easily accessible material to compost.
Q: Thanks for your recent column about composters you can buy. I built my own last year out of untreated wood pallets; it’s partially open-air and it’s about a 4-foot cube in a fairly sunny location. Now I am feeling uncertain about what to put in it; I’m also wondering what NOT to put in it! Can you advise me?
A: Congratulations on becoming a home composter! Organic compost can help sandy soil hold nutrients and moisture, and it improves drainage in clay soil. Glad to hear your compost bin is in the sun, as the heat helps break down the organic materials into useful compost for your garden.
Leaves are the most easily accessible material to compost. Remember that smaller particles break down more efficiently, so use a leaf shredder to chop up the leaves before adding them. You could even run over the leaves with your mower a few times. Be careful not to add leaves from diseased trees.
You can also add grass clippings, but it’s usually a better idea to leave them on the lawn. Leaving the clippings can significantly reduce the need to fertilize your lawn.
The advantage of adding grass is that the high nitrogen content will help speed up the microbial process. It’s a good idea to add grass if you’re starting a new compost pile. Using a mulching mower will cut the clippings into smaller pieces for quicker decomposition. If you have a high volume of grass clippings, mix with leaves to avoid the strong odor of decaying grass.
As a general rule, clippings from a lawn treated with herbicide or fungicide should be left on the lawn for two or three mowings before composting. However, some herbicides linger for up to 12 months, depending on the chemical, so be sure to read the label.
Many gardeners have easy access to wood ash, and it can be used as a lime source, but add no more than 1 cup per bushel of compost. Too much wood ash actually decreases the nitrogen in the compost, which defeats your purpose.
You can add plants from garden clean-up, but be sure the stems or non-woody twigs are ¼-inch or less. Keep out the badly diseased or insect-infested plants. Straw is also fine, but be sure it is clean straw or your compost will be full of weeds in no time! I compost my straw-bale garden, dirt and all. Occasionally I find a potato plant in the compost pile, but I just plant it!
You can compost weeds, too, although many gardeners are wary of weed seeds being transferred to their gardens. I avoid composting weeds for just that reason, as research shows the temperatures reached in most compost bins probably do not destroy the majority of weed seeds — especially in zones 3 and 4.
You can look to household waste for composting, too. Shredded newspaper (black and white ink only; no glossy inserts or magazines), coffee grounds and eggshells are all fine to compost. Fruit and vegetable scraps decay nicely, and you can toss in the sawdust of non-treated wood from your shop. Paper towels and tissues free of chemicals can be composted, and corrugated or flat cardboard is compostable, as long as it is torn into small pieces and soaked in water. Wax-coated cardboard (like pet food bags) is very slow to decompose and should be avoided. All tape and stickers should be removed from paper products.
There are household wastes you should not compost. Never compost dog or cat waste or human waste, as they can transmit disease. Chicken, rabbit and horse droppings are OK. Tea leaves are fine, but some tea bags contain nylon, which does not decompose. Do not compost meat, bones, fat, dairy products or whole eggs as they attract animals — and the odor is horrific! Spent charcoal contains chemicals harmful to plants, so leave that out as well.
Be sure the pile is moist, and turn it with a pitchfork once or twice a month, and you are on your way to beautiful, organic compost. In the warm season, compost may be ready in two to four months; an untended pile may take up to a year — or more. For more information, see the resources listed below.
Written by U of M Extension Master Gardeners in St. Louis County. Send questions to firstname.lastname@example.org.