Many cities and counties in the U.S., faced with a lack of landfill space, have discovered that giving away free compost and mulch is beneficial to everyone involved. Gardeners love freebies, so they scoop it up by the truckload to add to their gardens. I know people who have built all their raised beds with free city compost, and they are very pleased with the results. I’ve found some drawbacks, though, which depends on your area, what plant materials are used, and how clean they are. I try to always be careful when adding an unknown element into my garden.
How Free Municipal Compost is Processed
The free compost from your city or county isn’t processed like you would your compost pile. What they do here in Florida is grind organic material very small, mix it with native soil and pile it up for a year. It doesn’t really get turned much, if at all, and the only watering it gets is from Mother Nature. Sometimes, if they are running low, it doesn’t make it a year before it’s distributed to pick-up points. It’s not moist and crumbly like compost you make yourself. When I was in SC, there were more leaves in the free compost, and it was more black and crumbly, but here in FL, it seems to change with the seasons. At times, there seems to be very little organic material in the mix at all.
Insects, Diseases and Nematodes
I used free compost in my garden for years, simply as a soil amendment. It was a wonderful way to add organic matter to my worthless Florida sand, and it did its job. I wasn’t too concerned about insects, being a largely organic gardener, until I used it to plant tomatoes in buckets. When one plant died, I dug it out and found 23 white grubs in the soil that had completely destroyed the plant roots. The fact that these lived was a sign that the temperature inside the pile didn’t get high enough to kill them. I’ve also had container plants killed by nematodes, which would not have happened with year-old properly composted materials.
When you think about it, a lot of what goes into yard trash is diseased and dead plant material that you might not add to your own compost pile. When this is placed in the ground, nature can handle most of it, but not in containers. I started pouring several pots of boiling water through the containers before planting, covering them with clear plastic, and leaving them in the sun for a week before planting, which seemed to take care of these problems.
Extraneous Materials in the Compost
I’ve found some strange stuff in our free compost — bits of PVC, plastic, and pieces of beer cans are just a few. I even found a large piece of animal bone once — at least I hope it was an animal. It’s always wise to sift through and pick out any large pieces of extraneous materials before adding it to your garden. I’m sure they don’t take the time to empty all the leaf bags, and some people put more than just yard materials into those bags, which then gets ground up with the leaves.
The Best Use for Free Compost
In my experience, free compost is great as a soil amendment for anything you plant in the ground. If you are going to fill a raised bed with it, I’d solarize it for at least 30 days before planting. Also, send some off for a soil test, because it is going to need amendments, and you want to be sure it doesn’t contain toxic chemicals.
The easiest way to solarize it is to first slowly water it overnight to make sure the first 6 inches are saturated. The next day, cover it with clear plastic, seal the edges to hold in the heat, and let it sit in the full sun for at least 30 days. It’s actually better in areas with large nematode populations to solarize a bed for the entire 3 months of summer. If you can’t do that, solarize it for a month and add diatomaceous earth before planting. Remember, nematodes hate organic matter, so you may want to add even more leaf mold or layer leaves and compost to help combat them. Non-composted wood materials also use nitrogen to decompose, so you’ll want to watch for signs of nitrogen deficiency and add more as needed.
All-in-all, free compost from your local dump is a good deal. The time taken for a few precautions is time well spent when compared to the money saved. Contact your local extension service office to find out if you have free compost in your area.
USDA Cooperative Extension System Offices