Midcoast gardener Mary Dunn was feeling pretty good about getting her plants in and compost spread several weeks ago before the worst of the black flies emerged for the season.
Then it rained.
“After the rain I went out to plant something else and saw a piece of glass in my garden,” Dunn said. “I started looking around and I was seeing it everywhere.”
While glass is not a desired compost ingredient, there is no real cause for alarm.
“I can see why someone would have concern about things in their compost, especially glass,” said Nicholas Rowley, sustainable agriculture and horticulture professional with University of Maine Cooperative Extension and staff member of the Maine Compost School. “For the most part it’s nothing to be concerned about.”
Commercial compost available from garden supply centers or compost facilities around the state get their compostable materials from a variety of sources, Rowley said. That means it can contain a variety of items that can be a bit surprising.
Everything from dinnerware to plastic toys can end up in yard debris.
Then along comes the landscaper or yard company who collects it all.
“They can be sucking up the weeds and end up sucking up a Barbie Doll in the process,” Rowley said. “It can all make it into the ingredients of the compost and since Barbie won’t break down, pieces of her can still be there in the end product.”
Ideally, glass, metal or plastic items will be separated out during the sifting process of making the compost, but sometimes things slip through.
“Mistakes do happen and it’s kind of inevitable there will be little pieces of glass or plastic or metal that make it into the compost,” Rowley said. “There is only so much screening that can happen.”
If the compost ingredients were collected from somewhere that serves food, animal or poultry bones and crustacean shells could also break through. They will degrade over time but could be visible in compost until they do.
A small amount of inert ingredients will not harm your garden, according to Rowley, even though they will never break down.
The time to get worried, Rowley said, is if your compost contains more inert ingredients than actual compost. That, he said, will degrade the overall quality of the material.
To prevent getting subpar compost in the first place, Rowley recommends visiting the facility or store where you plan to purchase the compost.
“Look at it yourself and if it’s bulk, stick your hand into it,” he said. “If it’s dense, smelly, wet and warm to the touch, that’s when I would get concerned.”
Those are all indications the composting process is not complete.
Compost is ready for sale and spreading in your garden when it looks, feels and smells like soil with no flies crawling around on it.
Many facilities also have their compost tested and analyzed by a laboratory and those results are available to consumers.
Rare or not, Dunn is not pleased, but resigned to spending however long it takes getting the glass out of her garden.
“I don’t know what else to do,” she said. “My husband built a sifter so we are going to see if we can re-sift the compost [and] I am just going to keep picking it out.”
