Organic Answers Column - June 4, 2025 - tree trimmings

Shredded Tree Trimmings as Mulch

Shredded tree trimmings.

Year round there are uses for mulch in organic yards and landscapes. In winter it helps protect the roots of perennial plants, in spring it helps cover bare soil to slow the growth of weeds and to keep moisture around newly planted and growing crops, flowers, shrubs, and trees. During the growing season adding more mulch as the heat rises reduces the amount of watering needed. In fall it is useful when preparing for the cold season and provides a good medium for overwintering beneficial insects. All times of year mulches should kept away from the tree flares and trunks. If the zone around a tree or woody shrub is mulched, make sure that right around the plant is a very thin layer that won't interfere with the trunk flare.

Shredded native mulches (also called arborist wood chips) are the best choice. They insulate the soil and plant roots, prevent the winter weeds, have good balance of carbon and nitrogen, are loaded with nutrients, stay in place well, breathe properly and break down well to feed microbes in the soil.

Shredded hardwood. The consistency of shredded or chipped tree trimmings will vary
according to type of wood and if or how many leaves are in the mix.

An excellent and often overlooked source of native tree trimmings are all of those tree service trucks that run up and down streets after heavy weather or during an operation when the power companies are removing tree branches from the rights-of-way around the lines. They will typically unload the entire contents of the truck that catches the chips for you, for free. It saves them a drive to the dump or recycler and the cost of dropping off the load.

This image comes from a tree trimming company in Wisconsin that offers
the shredded tree trimming chips free. Know where you want the chips to
be dumped when you request them.

Another aspect of requesting a load of chips (one of those trucks can typically hold 10 - 13 cubic yards of chips) is that if you have more than you can spread, move them to a pile where they can stay undisturbed (or ideally, turn it once a month to introduce more oxygen to the process) and let them decay into the best compost available. More about that from an excerpt from The Organic Manual.

There are many of the other mulches on the market, some are good and some that are not so helpful. Here's a quick overview:

Rubber mulch from ground up tires contains toxic chemicals, doesn't break down to feed microbes and holds too much heat in the summer. Neither weed blocking fabrics nor plastic of any kind should be used. Mulch should touch the soil so that its breakdown into humus feeds the life in the soil.
Pine bark, especially the smaller pieces, blow and wash away, plus they contain natural chemicals that hurt soil health and plant growth. Pine straw or needles interesting do not have the same natural chemical issues, stay in place better and work well as mulch. Looks a little weird if you don't have any pine trees. Cypress is all carbon and breaks down very slowly. Not what we want. Rotting of mulch is an important source of natural fertility. Being harvested from wetlands and shipping across the country is also a concern. Cocoa mulch smells good but is expensive and very dangerous to dogs.
Pecan shell mulch is an OK choice, especially if aged, but fresh, new shells don't behave. Like pine bark, they blow and wash around and usually have some pecan meat left that attracts fire ants. Partially completed compost is good. When ingredients are still identifiable, this compost works well as mulch.
Shredded hardwood bark is not as good as shredded tree trimmings because of less nitrogen and trace minerals due to no protein tissue - buds, stems, cambium, leaves, etc. Lava gravel is an excellent mulch if you like the look, but be sure to avoid the plastic under it.
Colored mulches are made from ground-up wood scraps, siding, palettes and sometimes treated lumber, making them all carbon and totally unbalanced due to lack of protein/nitrogen. They actually rob nitrogen from microbes and soil health. Dyes used in these ugly products are also questionable in toxicity.

Here is the Mulch Chapter from Organic Management for the Professional by Howard Garrett, John Ferguson, and Mike Amaranthus.

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