What to consider when choosing organic mulches

This story was originally published in June 2020.

There are a wide array of organic options for mulches. These mulches come with the added benefit that as they decompose, they can add helpful nutrients like nitrogen and carbon to the soil.

“With organic mulches, I’m imitating what nature does with the forests,” said Tom Roberts, owner of Snakeroot Farm. “Nature makes mulch in the forest by adding leaves every year.”

Roberts gathers a variety of organic mulches from his neighbors throughout the year — for example, raked leaves — and keeps them on his land until he is ready to use them among his crops.

“All you have to do is be clever enough to think, ‘Who has what I can use for a mulch that to them is a waste product?’” he said. “That means your cost is really low.”

However, Roberts’s method does take advanced planning and preparation.

“It can be a yearlong process,” Roberts said. “Without planning ahead, it’s hard to do things right.”

There are lower-maintenance organic options. Bark mulches and wood chips, for example, are readily available at many garden centers. Wallhead said they are especially useful for landscaping. Treated options like shredded bark or wood fiber will last several years, but he said untreated wood chips are a less expensive option that are good to use in a landscape around well-established plants.

“I wouldn’t want to use fresh wood chips around tender [plants] — woody plants shrubs would be fine,” said Matthew Wallhead, ornamental horticulture specialist and assistant professor at the University of Maine Cooperative Extension. “Trees obviously would be good for wood chips. Perennial plants once they’re growing would be ok, but if you’re trying to grow something from seed, there could be some issues from the mulch tying up nitrogen in the soil.”

When it comes to organic mulches for vegetable gardens in particular, Garland opts for a mixture of bark mulch and compost.

“People oftentimes don’t think of compost as a mulch, but it can be a really effective mulch in terms of keeping the weeds down and helping the soil retain its moisture,” she explained. “It doesn’t accumulate like bark mulch does.”

However, bark mulch in particular tends to come at a higher cost and involve a bit of maintenance.

“If you use something like wood chips in the garden, you probably want to remove those before you [till] the garden for the next year,” Wallhead said. “At the end of the season or the beginning of the next season, [straw or leaf litter] can just be incorporated into the soil rather than having to be raked off.”

For landscaping, Wallhead said buckwheat hulls are also gaining popularity, too.

“They’re a very nice material for mulch because it has a small particle size and it’s black so it adds a very nice contrast and has a very smooth appearance,” he explained. Some people don’t like that chunky look of bark.”

Gallandt said to know the difference between straw (“the brown stuff that is used for animal bedding”) and hay (“the green stuff that is the food”), which can have seeds leftover in it. Even regular bales of hay can have so-called “volunteer seeds” leftover in the stalks and chaff.

“You can get mulch hay, that can be a very good source of mulch,” he said. “It tends to have a little bit more nitrogen to carbon in it [and] breaks down a little bit faster. People worry sometimes about bringing the weed seeds in the hay [but] it’s not something I would be overly concerned about. Most of the weeds you find in a hay field are not the species that are common in a garden.”

In order to save money on organic mulching options, Garland said to look around your yard for whatever is available — for example, fallen leaves.

“Shredded leaves are really, really good mulch,” Garland said. “I highly recommend that. They’re free, they’re there in your landscape. Put them in a plastic trash bag, roll it around and crunch it up, have your kids jump on it. You can also run over with a lawn mower.”

Grass clippings can be a great mulch, with certain stipulations.

“The best case scenario is you want grass clippings from your lawn,” Garland explained. “[However,] it might matte, it might blow around a little bit and they may actually have weed seeds in them [and] herbicide residue can have a pretty big negative impact on your garden.”

Pine needles can even be an inexpensive and effective mulch if they are available; because they tend to acidify soil slightly, they are best for crops like blueberries, rhubarb and asparagus.

“I really like that as an option especially if it’s readily available in your landscape,” Garland said. “If you’re raking up the pine needles, you might as well use them. They may acidify your soil a little bit but not as much as people think. If they’re worried about the acidity of the soil, have a soil test done.”

One organic mulch that Garland recommended against, though, is peat moss.

“It can dry out and matte and become hydrophobic,” Garland said. “Unless it is incorporated into the soil, I don’t think it’s a highly useful mulch or soil amendment. It’s [also] not an environmentally friendly product.”