Mulch Is Mulch, Right?
I recently had the opportunity to work for a couple weeks in a large private orchard miles outside of town in a remote area. Water is precious in such a setting, as well as the energy needed to pump it to the surface. To help mitigate the loss of water brought to the surface, we were tasked with applying a thick layer of organic mulch to reduce evaporation and help even out the water delivered by the drip irrigation system. We spent a fair amount of time researching and choosing the right product to use. Why? Because not all mulch is the same.
Let’s begin by discussing what mulch is used for. Moisture retention, check. Buffering soil temperature spikes, check. Weed suppression check. Holding down and covering a more aggressive weed suppression such as fabric, check. Making your yard look pretty and finished, check. Building soil, huh? Here is something that only organic mulches can do. As organic mulch breaks down at the surface, microbes, soil critters, and water carry the leftovers down into the soil below, creating that beautiful dark stuff we like to plant in. Oh, gravity helps a little too.
Many things can be considered mulch, including stones, boulders, and even living plants such as groundcovers and some grasses. If the ground covering performs one or more of the tasks listed above, it could be considered a mulch of sorts. Yes, even grass, such as buffalograss, will buffer soil temperatures, suppress weed growth, and even build soil. It’s been said that one ryegrass plant can grow several miles of tiny little roots through the soil in the course of one season. Think about how many more roots a buffalograss plant will produce every year as its roots burrow several feet into the soil each year. Living groundcovers shade the soil, keeping it cooler and suppressing weed growth by blocking the sunlight. Win, win! Choosing groundcovers that are also low water use makes it a win, win, win!
So, let’s get back to organic mulches. What makes the decision so difficult when choosing the right one? Because one misstep could mean disaster. There are many choices, but let’s focus on the most likely. Let’s say you are an avid gardener, and you thrive on the idea of no inputs or outputs past your property line. You are going to save all your trimmings and whatever doesn’t go directly into the compost pile, gets chipped up and used elsewhere in the garden or on pathways. This is a great idea, but you still will need to be careful about what you are chipping up and how you are using it. More on that in a moment.
Moving up the cost scale a tiny bit, perhaps you have seen one of the local or national tree trimming companies working in your area and you notice they have a nice big load of chips in their truck. You inquire and hear something like, “We are always looking for places to dump this stuff.” Bingo! Or, you notice that huge pile of chipped up landscape waste at the local landfill or transfer station. It’s usually free, but you may have to ask your cousin Jerry if you could borrow his ’72 Ford pickup to haul a load. You can also have a dump truck load delivered for a fee. Sounds like a winning situation. Not so fast . . .
There’s a little thing called allelopathy. By definition, allelopathy refers to the chemical interactions between plants, where one plant releases substances that affect the growth and development of other plants. These substances, known as allelochemicals, can have both inhibitory and stimulatory effects. While often associated with negative impacts like weed suppression or reduced crop yields, allelopathy can also be harnessed for beneficial purposes, such as creating more sustainable agricultural practices. Whew! Thank you, AI! Quite a mouthful, but you get the idea. Putting down the wrong organic mulch, especially one you have no idea what’s in it, can be devastating. I have experienced this on my own property. I received several loads of chippings from a tree trimming company and used them for weed suppression and soil building in a few areas of my yard. On a whim, I decided to plant a few veggies in a couple of areas. The plants I seeded never came up and the ones planted as starts either died or wished they had. As an added bonus, I got a nice new crop of Arizona ragweed wherever the mulch was spread.
Organic mulch is always a good idea, just be selective. If using chipped tree trimmings, even your own, try to compost it for at least two years to help leach out the allelochemicals before using it around any food crops or desired landscape plantings. On the other hand, if you want a good product that you can obtain a report card for, try the sand and gravel yards. Look for a composted product that originates in Phoenix from a company called GroWell. It’s a good product made from mostly pine and fir bark and sawdust. I have been using it in all my raised bed projects this year with great success. The composted product mixes well with soil and should stick around for a couple of years at least. There is one yard that sells a less seasoned product they call playground mulch. This makes a great top dress around your plants for all the reasons we’ve been discussing. Do your research and choose carefully and you will have great success using organic mulch in your yard.
See you around the mulch pile!
The HortiCoach