What is the Best Mulch for Western Washington?

Mulch in action.

Mulch is a crucial part of the garden. As well as saving you work by sealing out weeds, it can help build healthier soil by adding nutrients and promoting natural soil development. So, what’s the right choice?

What are your options?

On a basic level, mulch is anything that goes over the soil. That even includes carpet or cardboard put down over the ground to suppress weeds.

When it comes to your garden, you probably don’t want anything that extreme; natural is better. Some common natural options are gravel, bark and compost.

Gravel is often used in desert environments, but here it allows weeds to come through. Bark suppresses weeds but takes a while to break down and worsens soil. In comparison, compost breaks down more quickly and offers nutrition to plants as worms turn it in to the soil.

Another option is arborist chips. Made from chipped up tree debris, they offer less regularity and break down more slowly as a result. This is good for the soil as it provides extended protection and natural nutrients as they break down. Arborist chips have a coarse visual texture, so they are more suitable for larger areas.

In general, mulch works like fertilizer: the less processed it is, the better for the soil. Less processed materials take longer for organisms in the soil to break down, providing nutrients over a longer period and building up the structure of healthy soil. For this reason, leaves and other organic material from your garden can also work as an effective form of mulch, assuming they are not too tightly matted to prevent growth and water penetration.

What to choose

For gardens with trees and shrubs where you want to keep down weeds, arborist chips can be a great choice. For areas where you need to infuse the soil with more nutrients, compost can be a good choice as it is richer and its nutrients are readily available to plants.

But you don’t have to choose, according to Washington State University experts. You can use a two-layer approach, a “mulch sandwich,” where you apply compost as a top layer to amend the soil and then cover it with wood chips to protect the soil and compost.

What to be careful of

You generally don’t need to worry about the trees that wood chips come from, but be sure the chips don’t include invasive species like ivy. In general, keep an eye on any mulch to make sure it doesn’t bring in weeds with it, although the consistency of mulch will make it easier to pull out any that do sprout.

Also be sure to leave space around the trunks of plants, having mulch right up against them can cause the bark to rot and then the plant may die.

Why to mulch

Besides the common benefits of reducing weed growth and protecting plants, mulch can play an important role in developing your garden naturally. According to WSU scientists, there’s increased recognition that it’s better to add nutrients to soil by placing layers on top of it, instead of disturbing the soil with digging in amendments. This allows natural organisms to do the work for you and mimics the natural formation of soil.

Mulch, as well as improving the soil, keeps the soil cool. This slows the germination of weed seeds and slows the evaporation of water. It also protects the underlying soil from the impacts of raindrops and slows water runoff. Both factors lesson the likelihood of erosion, especially important in this climate.

The best mulch is that which provides your plants what they need for years to come. Visit our resources page to find some local brands we use.