Ask the Contractor: Everything you need to know about mulching

Photo courtesy of Soft Surfaces Ltd. http://www.softsurfaces.co.uk/surface-types/rubber-mulch

Photo courtesy of Soft Surfaces Ltd. http://www.softsurfaces.co.uk/surface-types/rubber-mulch

Spring Countdown: We have Spring Training — we have spring fashion trends — we have spring hairstyles — we have spring academic calendars — we have spring color trends and most importantly we have spring beginning Monday March 20, 2017. The buds are popping, the grass is greening, the bulbs are springing up, the air is fresh, and “springtime” the season we love, the rejuvenation, renewal, and regrowth of our plants and flowers and the hills are alive.

What better time to address several questions that came in over the past few weeks about mulch: the types and when mulching should be done.

We are new to Arizona. Do we mulch in the high desert?

— Ann and Clark, Prescott

Yes, we mulch and mulching should be done after planting is completed. Acceptable mulches include shredded hardwood bark, pine needles, coarse compost, pecan shells and shredded cypress bark. According to several of our local landscapers shredded native cedar is the best of all. Mulch should be at least 2 inches deep on top of planting beds, and deeper around larger plants. Mulching helps hold moisture in the beds, controls weeds and buffers soil temperature. It also enriches the soil as it decomposes.

We have mentioned this in the past and will mention it again: do not use plastic sheets or weed blocking material in your plant beds. These artificial materials provide nothing beneficial and the plant’s roots system can cook from the heat buildup. Plastic also cuts off the oxygen needed by the soil.

The best mulch for any site anywhere is recycled plant material (leaves, twigs, spent plants, buds, bark, flowers and other plant debris) that grow on your property. The second-best choice is purchased shredded native cedar.

Keep in mind you want the mulch to break down. That’s what creates the true natural food for feeding microbes and plant roots.

Pine needles make a good mulch but look a little out of place when used on a property where no pines are growing. Lava gravel makes a good mulch and has the extra benefit of keeping squirrels and cats out. It’s interesting that the most popular mulch material, pine bark, is not very good. First, it won’t stay in place — it washes and blows away. What does stay breaks down into a mucky material that does help plant growth.

For shrubs, trees and ground covers, use at least 1 inch of compost and 3 inches of shredded native tree trimmings or shredded hardwood bark. Mulch preserves moisture, eliminates weeds and keeps the soil surface cooler which benefits earthworms, microorganisms and plant roots.

Are all cedar mulches created equal? The main thing I want to do is repel roaches and other bugs from around property.

— Louis, Prescott

The fresher the better with cedar mulch. All cedar trees make excellent mulch, but I prefer mulch made from our native cedars. Freshly cut cedar mulch has more oil in the wood, which provides fragrance and repels insects. Repelling insects is a nice side benefit, but the primary purposes of mulch are to protect the soil and help build humus.

Can grass cuttings be used as mulch, or will this result in excessive weeds?

— Rick and Anne, Cottonwood

Grass clippings can be used as mulch unless they are applied in a layer that is too thick. When clippings are piled too thick, they do not get enough air circulation while decomposing and will smell terrible. They also won’t form humus or help plants well. When grass clippings are used as mulch, the thickness should be barely enough to cover the soil. The best way to use grass clippings is to leave them on the turf as you mow. They break down well there, especially if you follow an organic landscape program, and they feed soil microbes. The net result is better-looking turf while using less water and fertilizer.

I just saw a brochure about rubber mulch made from tires. I thought it was a great idea for recycling a material that is difficult to dispose of. This product, while very durable, would probably retain heat and not keep plants as cool as most mulch does. What do you think about it?

— Chuck, Prescott Valley

Our landscapers are very much against rubber tire mulches. They contain toxic materials and don’t work well. They do absorb and hold too much heat, they don’t break down and turn into humus and the look is not attractive. Also, some recycled varieties may leach chemicals (some toxic) that are harmful to plants. Rubber mulch, like some organic mulches, is a hazard if ignited and rubber mulch is more difficult to extinguish.

I want to use colored much to match the exterior of my home. I have heard colored mulch is not good.

— Chris, Prescott Valley

There are several bad mulch choices, such as pine bark, cypress, rubber and cocoa shells. But there is one that deserves special mention in the do-not-use category — the red- and black-dyed mulch. Colored or dyed mulches are ugly and not good to use. They are made by grinding up dry wood waste and then dying it. The chemical binders and dyes often used contain toxic heavy metals and other contaminates such as algaecides and fungicides to retard decay and make the color last longer.

Colored mulch does not support the variety of beneficial microbes required for healthy soil and plants as other organic mulches such as a good shredded native tree trimmings. To absorb the dye, the dyed mulch has to be made from dry wood. This may be unused construction wood scraps, mill waste or old pallets. Some vendors grind up and use the hazardous treated wood so the colored mulch may be an unwanted source of arsenic (studies in Florida have found levels of arsenic in colored mulches to exceed federal safety limits in over 75 percent of the samples tested). Whether contaminated or not, dyed mulch is wood with no protein to prevent nitrogen robbing from soil and plants. These red and black products are bad to use horticulturally and are tacky-looking.

Remember to tune in to YCCA’s Hammer Time twice each weekend Saturday and Sunday at 7 a.m. on KQNA 1130 AM/99.9 FM or the web kqna.com. Listen to Sandy and Mike talk about the construction industry and meet your local community partners and contractors.