Local Gardening: Let’s Talk Mulch

When I started this column back in March, one of the first things I wrote about was the use of mulch and no-till gardening. These two things go hand in hand, and this is the time of year when they are most important.

Soil evaporation becomes the biggest enemy of the home gardener as the weather gets hot and dry during the summer months. You can beat soil evaporation by applying thick mulch on top of the soil.

Nature abhors bare soil. Anywhere healthy soil gets exposed to the surface, nature quickly covers it up with weeds. Gardeners who till their soil and form it into neat rows find themselves fighting nature by constantly pulling weeds. The sun beating down on the surface kills beneficial bacteria and forces earthworms to retreat to shadier areas. More importantly, the sun evaporates moisture in bare soil more quickly. The bare soil gardener often complains about having to water their plants so often.

There is a better way, but first, a little science.

I reached out to Fayette County Ag Extension Agent Scott Willey for some data on soil evaporation. He put me in touch with Dr. Jake Mowrer, a soil science expert at Texas A&M University’s Soil Crop Sciences Department. Mowrer provided data that shows soil evaporation is a function of many variables including temperature, wind speed, humidity, soil type and soil texture.

Moisture evaporates very quickly from sandy soil and less quickly from loamy soil. Moisture evaporates the slowest from clay soil. Clay soil has an unusual characteristic in that moisture evaporates in stages. Locals with black gumbo soil can probably attest to this. Blackland will hold nearly all of its moisture for several days after a rain. It will then dry out a little and retain that level of moisture for another several days. Then it will dry out a little more and hold for several days, and so on. To visualize this, check out the chart below Mowrer provided.

Soil dries out faster in windy conditions than on calm days. Humidity plays a huge role as well.

“We will see very little evaporation on a 95% humidity day when the temperature is 100 F but quite a bit when it is 80 F with 5% humidity,” Mowrer said.

Back in the 1940s a lady named Ruth Stout pioneered thick mulch gardening methods. She used straw for mulch and laid it eight inches thick on top of the soil. She found that her plants grew bigger and faster and she had to pull weeds and water less often. Gardener Paul Gautschi started promoting a thick mulch method called “Back to Eden” that used wood chips for mulch. Both methods serve to slow soil evaporation and build the soil at the same time.

You do not want to mix mulch with the soil, especially if you’re using wood chips. Wood mixed in the soil begins to compost and robs available nitrogen. You want the mulch on top of the soil, where it breaks down slowly and add nutrients to the soil over time.

You may be thinking, “But bags of mulch cost $5 each, and if I have to cover my whole garden with eight inches of mulch, that’s going to cost hundreds if not thousands of dollars.”

Luckily, we live in Fayette County, which has an outstanding recycling program run by the county government. They produce and sell a good quality native wood mulch. Best of all, it’s really, really cheap.

Every time a strong storm blows through the County and knocks trees into the roadways, County workers go around and remove those trees. They haul them to the Recycling Center in La Grange and stack them up into massive piles. The County also allows property owners to dump brush there for a fee.

Once or twice a year, the County hires a company to double-grind all that material. The ground-up material gets piled up into a huge mountain, where it ages and breaks down. Workers at the recycling center use a skid steer bobcat to load the material onto pickup truck beds or trailers. They sell the material for $5 a scoop. One scoop from the County’s bobcat just about fills up the bed of my half-ton pickup.

“It’s mostly elm, oak, hackberry, some cedar and maybe a little bit of pine,” said Pct. 4 Commissioner Tom Muras, who oversees the County’s recycling program..

A lot of people seem to think that cedar and pine are bad to use for mulch. All of my research indicates this is not the case. Cedar mulch contains natural chemi-cals that deter some insect pests and diseases. It even deters some harmful soil nematodes.

Pure pine bark mulch, like the kind commonly sold at landscaping centers, is not the best mulch, mostly because it doesn’t stay in place. Wind and water move it around. Also, pine bark mulch contains some natural chemicals that can negatively affect plant growth.

However, the other parts of pine trees make wonderful mulch, especially the needles. Don’t be afraid to mulch with pine needles if you have them on your property. The little bit of pine in the county’s wood mulch contains all parts of the tree, so I don’t see a problem with it.

Muras said the County mulch does not contain any creosote posts, treated lumber or other construction materials.

“Anytime someone dumps limbs over there, someone from the County is there to supervise, and we never let any of that stuff get in the pile,” Muras said.

I occasionally find a piece of plastic here or there in the mulch but never more than I can easily pick out. Sometimes there are larger pieces of wood that I throw to the side. I once found a 10 lb. hunk of cast iron in it, which was kind of interesting (and made me wonder what it did to the tub grinder). All in all, it’s a pretty clean product and definitely worth the price.

You can create a new planting bed for next year by simply piling six to eight inches of mulch on top of the ground. I like to lay down some cardboard or newspaper first, to choke out the grass. Let the mulch sit for six months to a year and you will have a wonderful bed.

I use the mulch to cover walkways in between the beds in my garden so I don’t have to mow the grass. It creates a wonderful habitat for spiders and other beneficial insects. I’ve also noticed a big racerunner lizard who likes to live in the mulch.

You might wonder, “Well that’s nice, but how am I supposed to till the garden next season?” That’s easy – you don’t. Stop tilling today. Once you get a bed established and maintained, you don’t need to till. Tilling destroys the earthworm habitat and beneficial fungus network you create by mulching with wood chips. Next season, such push a little mulch away from the spots where you need to plant something. If planting seed, make a trench in the mulch to expose the soil surface then plant as normal. When seedlings emerge, push the mulch back to cover the soil.