You’re probably mulching wrong. Here’s 5 things to know about how to mulch properly

Picture of Paul Cappiello Ph.D.

Paul Cappiello Ph.D.

Yew Dell Botanical Gardens Executive Director

Ok . . . you caught me. I fully realize that March ended at midnight on Friday but since so many of us are still firmly entranced by both the men’s and women’s college basketball March Madness, you’ll forgive me for helping myself to a little poetic license . . .

In all the world of gardening, mulching represents such an Arthurian-scaled double edged sword that I can’t let a spring go by without an annual rant. I mean a well-conceived and executed shot defense is a thing of beauty, just like a well mulched garden. But bad mulching is a bit like your shot defense devolved to the level of poking the shooter in the eye or running them down with the mobile soft
pretzel cart. Not a pretty sight.

So let’s huddle up and review a few basic rules of mulching in the garden.

1) Friends don’t let friends mulch badly.

Proper mulching is so easy and follows such logical thinking that understanding a few basic rules is all you need. But I get it. We’re all busy. It’s hard to believe, and yes, it does pain me to have to admit it, but it seems not everyone starts and ends every spring day thinking about and strategically planning their mulching projects. I can’t imagine what is more important than mulching . . . keeping alligators out of your drainpipes or setting up the Bigfoot monitoring camera . . . ? They’re probably close seconds.

But this is where you can exercise your civic muscle. Rather than let your neighbors commit hostile, mulch-related inflagrations, you can help them understand the finer points of mulch philosophy. Really, they want your advice. After all, what neighborhood would be complete without that one, brave gardening crusader walking up and down the block during the dinner hour, knocking on doors and kindly and casually pointing out the inadequacies of your mulch application or lack thereof. Trust me – they’ll love you for your altruistic efforts.

2) Leave the landscape fabric on the shelf.

If your goals in gardening are to unnecessarily cost yourself money, waste resources and generally to cause yourself headaches for years to come, landscape fabric is right up your alley – but otherwise, it’s a terrible idea. Legend has it that putting down fabric before you mulch has magical powers including suppression of weed growth, eradication of adolescent angst and solving unified field theory. In reality, the weeds grow just fine in the mulch above your fabric, that oh-so-natural-looking jet-black fabric has a nasty habit of sticking up through the mulch after a while, and it has a tendency to get wrapped around every garden implement from an edger to rototiller, manual hoe and your worn out Converse All-Stars now relegated to a second life as garden attire. There is benefit to vegetable gardening through fabric or film mulch but that’s a totally different animal and does not involve placing mulch on top of the film/fabric.

3) Volcanoes kill trees!

The origin of the practice of volcano mulching is shrouded in the mist of history, but whoever is to blame, I think they must have had the charisma of PT Barnum and the morals of the Music Man’s Harold Hill. Let’s make this one easy – piling up mulch 1-foot, 2-feet or more around the base of a tree’s trunk is a very, very bad idea. It reduces moisture and air exchange for the roots of young trees. It entices trees to produce adventitious roots in the mulch layer where they are more subject to drying out. It provides a perfect place for rodents to hang out and chew on the tree’s bark over the winter months. If your landscaper is engaging in volcano mulching, it’s time to get a new landscaper.

4) Mulching to conserve soil moisture.

A well-placed layer of organic mulch does a nice job of reducing evaporative loss from the soil’s surface. A proper mulch can also help retain a bit of that summer shower or pass by the irrigation jets by holding the water around and letting more of it seep into the soil.

Of course, this requires that you use a mulch that is up to the task. You want something that will stay where you put it and that will let rain/irrigation water pass through to the soil. Using a mulch that crusts over in the summer can result in sending all that valuable H 2 O out to the street and down the storm sewer rather than soaking into the ground. Be careful of ground-up hardwood or cypress mulches that can form a crust as they break down. They may need to be roughed up with a rake or hoe from time to time. Better yet, avoid them altogether.

At Yew Dell Botanical Gardens, pine straw is one of our favorite organic mulches. It is light weight and easy to carry around the yard. The slugs don’t like it so it will keep your hostas from being chewed to bits. Once it settles into place in the garden bed it stays in place. And most importantly, it allows water to pass through. We also like pine fines, a product made up of pine bark pieces below about one half inch across. It doesn’t work well on slopes where it can wash away in heavy rains. But on flat ground it is fabulous. Makes a great soil amendment too!

5) 2-inch maximum mulch depth.

We spend tons of time preaching about not planting too deeply, a practice that can seriously impair root growth due to limited gas (air) exchange between the root zone and the air above. Mulching too deeply can have the same impact as planting too deeply. Before mulching, go out and check your beds to see how much mulch is already there from last year. If you have 1 or 2 inches in place, maybe all it needs is a clean up and a quick rake rather than spending time and money to add more. 

This article was originally submitted to the Courier Journal on March 29, 2023.

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