The Green Gardener Series -
Mulch: The Priceless Ingredient for a Healthy Garden
by Ann Barklow

I have been using mulch in my garden and the gardens of my clients for the past ten years. It is to the point now that I can’t stand to see bare soil. I get this almost uncontrollable urge to grab a pitchfork and throw a layer of mulch on it. I had the distinct privilege of hearing Dr. Jim Downer, Farm Advisor with U.C. Cooperative Extension, speak on mulch at the last Southern California Horticultural Association meeting in Los Angeles. Listening to Dr. Downer’s eloquent talk on the benefits of mulch, made my obsession even worse.

The benefits of mulch

•  block weed growth by keeping the sun out
•  keep the soil cool and moist
•  feed both the soil and the plants as it breaks down
•  repels insects
•  eliminates mowing around trees preventing damage

You don’t need to worry about thick mulches robbing your soil of nitrogen either. Nitrogen depletion only happens to the soil if you mix the undecomposed organic mulch into the soil, instead of placing it on top of the soil. The trick is to lay the mulch down thick - then forget about cultivating the soil. The constant aerating of soil is not necessary - let the earthworms do that for you.

What mulch should you use?

Since my garden and the Manhattan Beach Botanical Garden where I volunteer is covered with thick coarse shredded tree trimmings, I was anxious to ask Dr. Downer what he thought of our mulch. He loved it!

Dr. Downer recommends a coarse textured organic mulch rather than a fine one and his reasons make sense. He explained that moisture can infiltrate through a course texture better - and this is a good thing because you don’t want a mulch to hold too much water since moist mulch can germinate weed seeds that blow in on the surface. A fine textured mulch can also sheet off completely during wind or rain and is especially ineffective when used on slopes. It also breaks down quicker than the coarse mulches, so it would need to replaced more often.

Another thing I learned from Dr. Downer was that his studies show that Eucalyptus tree trimmings do not inhibit plant growth. This is a big relief because it is difficult to find a load of tree trimmings from our local tree service without a few Eucs in it.

Lay it on thick!

“Some mulch is better than no mulch”--- doesn’t apply here. A thin, one to two-inch layer of mulch will encourage weed growth, so if you are going to mulch you need to lay it on thick.

Dr. Downer recommends six to eight inches so that when it decomposes it will still be at the preferred depth of four inches. That’s a lot of mulch! I took a ruler to the botanical garden to demonstrate to our mulching volunteers how deep eight inches is, and they said it would take them forever to mulch. However, when I told them we would have less weeds - they grabbed their pitchforks with enthusiasm.

Spread the mulch around your trees and shrubs, and throughout your flower beds, and wherever you have bare soil in your garden. Mulch looks great by creating a texture next to hardscape, buildings, and around plants set in lawn. Be sure to keep the mulch away from the bark of hardwood plants because it will rot them. I like a slight downward slope around the plant to keep the much from touching the trunk. In some areas, such as around small flowers or on slopes, it may be impossible to place mulch at 6”, so in those situations just put as much as you can. When designing a new flower bed or planting in containers, be sure to keep the depth of the soil level low enough to hold the mulch layer on top.

Get Free Mulch

One of the best sources I know for free mulch is my local tree service. If you call your local tree trimmers, often they are happy to dump a big load of mulch for you right in your driveway or on the side of the street. You’ll probably have more than you need and might want to share it with a few neighbors. Make sure you have a good wheelbarrow and pitchfork and leave yourself a few days to spread it out. Sometimes you can request a half load. Tree companies are always looking for ways to dispose of their chips so you will be doing them a favor. I ask them to keep pine needles out or to a minimum because I don’t care for them as a mulch.

There are other organic mulches available, too. My friend Charlotte goes to the local feed store to purchase bales of hay for seating for her outdoor parties. “To dispose of the hay, we just spread it around the yard. It reminds me of a farm and let's me fantasize about living on one for a brief moment in time. The birds love it, too. It makes great nests.” Charlotte’s garden is shady, but if you use hay in a sunny location it is best to water the bales and let them sprout any seeds that are present before you spread them. In areas where weeds aren’t a big problem finer mulches such as Cocoa mulch, dried grass clippings (no invasive grasses), or leaves work great. (Cocoa mulch can be toxic to dogs, so please use with care). I stay away from redwood chunks because they break down too slowly and I want the soil to benefit from the decomposing mulch.

Mulch is the priceless ingredient found missing in many of the troubled gardens I consult on, especially here in Southern California where many of our soils are low in the organic matter that plants need. Part of the trouble may be that we have believed the myth that leaves and organic matter will attract pests and that it “looks messy” - so we rake it out, leaving the soil and surface roots exposed to erosion, temperature and moisture fluctuations and taking away nutrients our plants need to survive. Learn to ‘leave the leaves' and when you dead-head your flowers - just let them fall onto the soil, like nature intended.