Your guide to the best organic mulch options

Bare soil is a bad thing, so any natural mulch is better than no mulch. Why am I so negative about some mulches and positive about others, especially shredded native tree trimmings? Let’s review the negatives about the poor and so-so choices first.

Shredded rubber tires claim the position of absolute worst choice. They hold heat but not water, and they don’t stimulate beneficial microbes. Plastic sheets and weed-blocking fabrics don’t control weeds well, and plant roots are damaged from heat buildup. Plastic also fouls up the flow of oxygen in and carbon dioxide out of the soil.

The second worst choice is ground-up and then dyed lumber. You probably know this stuff as the ubiquitous black and red mulch. It’s horrible. Chemical contaminants are one issue, but more importantly these ugly mulches are nothing but ground-up wood products ― mostly cellulose made of carbon — and they contain no protein, a source of nitrogen. This imbalance of carbon to nitrogen causes nitrogen drafting from the soil and yellow plants unless lots of fertilizer is used.

Pine bark washes away too easily.
Pine bark washes away too easily. (Howard Garrett)

The third-worst choice is pine bark. It has a bad habit of blowing and washing away. Besides not staying in place, natural chemicals such as terpenes are quite harmful to the beneficial life in the soil (although they help protect the tree when on the trunk of the tree).

Cypress is not high on my list because it doesn’t break down well. We want mulch to decompose. That’s what creates the true natural food for microbes and plant roots. There’s also an environmental issue of depleting the native wetlands.

Pine needles makes good mulch, but they look a little out of place when used on property with no pine trees. Pecan shells are so-so but also move around too much, and fresh shells can attract fire ants.

Lava gravel is the only gravel that works well for mulch. It works almost as well as plant-based mulches and helps to keep the neighborhood cats out of the beds.

Shredded hardwood bark makes good mulch.
Shredded hardwood bark makes good mulch.

Shredded hardwood bark is a good choice. Like the shredded tree trimmings, it stays in place well, looks good, smells good and breaks down properly.

The best mulch is recycled woody plant material. Our native cedar is one of the best choices. It stays in place, breaks down well, provides fragrance, repels insects, and feeds soil microbes beautifully. All parts of all cedar trees make excellent mulch. A mix of tree species in the shredded mulch is also just fine.

Some companies grind the rough-textured shredded tree trimmings into a finer texture and even add compost. That makes prettier products, but the material right out of the tree care company’s grinder is fine for all plantings other than very small transplants. I use compost for them.


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