Mulches have two primary functions – they suppress weeds and they act as a protective blanket on top of the soil, slowing soil moisture evaporation and mitigating soil temperature fluctuations. How well mulches do those jobs depends a great deal on the type of mulch. You’ll find a huge selection of mulch types at garden centers and local nurseries. Here’s a quick guide to mulch types and their individual pros and cons.
Wood chip mulches – Chip mulches come in three sizes – large, medium and small.
Large chips often do not settle well, leaving spaces between and under each chip. The spaces allow sunlight to reach and germinate weed seeds on the soil surface underneath the mulch. And the spaces also provide room and shelter for pest insects to lay their eggs.
Small chips, less than 1 inch square, are lightweight and easily blown or raked away.
Medium chips, about 1 inch square, have enough weight to remain in place and they will settle into a uniform mat with few spaces. A 3- to 4-inch layer of medium-size chips will suppress weeds and prevent moisture loss well. Plan on topping off the mulch layer at least once a year.
Wood chip mulches will decompose over time, adding nutrients back into the soil and also acidifying (lowering the pH) of our highly alkaline soil a bit.
Cocoa hulls, coco fiber and coir mulches – Cocoa hulls look and smell good, but they’re toxic to dogs. Coco fiber and coir mulches do a good job of weed suppression and moisture conservation, but their rough texture makes it hard to rake and blow out debris. Coco fiber and coir mats make good tree ring mulches; weed suppression is excellent and irrigation water will soak through the mat into the soil.
Cedar shavings – Cedar shavings smell good and look fluffy, deep and high at first. The shavings will mat and knit together within a few months, sometimes creating a tight, impermeable surface that water cannot penetrate. The natural reddish color also fades fairly quickly to dull gray. Debris can be blown off cedar shavings, but raking out fallen leaves is not easy. Cedar shavings are not the best choice in our climate where we constantly must monitor and maintain soil moisture.
Rubber – Rubber mulches stay stable for up to 10 years, unlike natural wood product mulches which need annual replacement or topping. The mulches are made of used tires. Using rubber mulches near edibles is not recommended since the products can leach trace amounts of toxins and zinc into the soil. Landscape cloth should be placed underneath rubber mulches to prevent the particles from getting into the soil.
Rubber mulch tree rings work extremely well in suppressing weed growth around tree trunks. The solid surface rings can be mowed over, but irrigation water will not penetrate the soil around the trunk.
Rocks – drought-tolerant landscapes often use rocks as mulches and as decorative accents. Rocks look good, they’re permanent, and they do suppress weeds. Rocks also absorb, retain and reflect our intense summer heat, sometimes becoming too hot to touch. Place rock mulches away from plants and structures or use them only on the shaded north side of the garden.
When laying down any type of mulch, keep the product at least 4 inches away from tree trunks and plant stems to prevent wet mulch from rotting the plant wood.
Send Elinor Teague plant questions at firstname.lastname@example.org.
Concerts in the garden
The Clovis Botanical Garden is once again putting on a “Twilight Thursdays Concert Series” Sept. 14 through Oct. 5.
Time: 7 p.m.
Place: Northeast corner of Clovis and Alluvial avenues
Amenities: Admission and parking are free. Cold drinks and dessert are available for purchase. Bring your picnic dinner and chairs and enjoy great music in the lovely garden.
Details: Check the garden’s website, clovisbotanicalgarden.org, for a list of performers.