What? Did I really say that? The "Dangers" of mulch? How can mulch be dangerous?
Mulch is more than a pretty face, it does so much more than just pretty up your gardens- it does however, have a dark side.
Let's talk about the benefits of mulch first. It does make your garden look pretty! I always say that mulch is like the ice cream with cake. Cake is yummy, but cake with ice cream? Sign me up! I"m there! So many times when Eric and I first started this business clients would say to us after we mulched "I can't believe what a difference that makes!" and it's totally true.
Aside from that, mulch is a true work horse. Mulch keeps the weeds down in your beds. I know, you're thinking "I knew that". I bet you did, but did you know that mulch also helps prevent evaporation in the bed - meaning you don't have to water as often? Along with helping to keep weeds down and helping to prevent moisture loss in your beds, probably the most important function of mulch is to insulate plant roots. Having mulch on your beds helps to insulate plant roots from the crazy fluctuating temperatures we have here in Connecticut. One day it can be 40° and the next it can be 80° This seems to be especially true in the spring when Mother Nature seems to be shaking off the cobwebs of winter and waking up again. Plant roots are susceptible to temperature fluctuations just as we humans are. Mulch as an insulator can make a big difference in the overall health and longevity of your plants. Last but not least, mulch breaks down over time to add organic content to your garden beds. This adds tons of nutrients to your beds that we just can't mimic in fertilizer.
With all that goodness, how can mulch be bad?
Improper mulching can not only look bad, it can cause harm to your garden. For the most part, your perennials are pretty safe, but shrubs and trees not so much. Perennials are troopers, you can mulch your garden early in the season and those little guys will just pop right through the mulch, but it's different for trees and shrubs which are what we call "Woody Ornamentals". Trees and shrubs don't like to be hugged so tightly by the mulch, they need a little "breathing room" so to speak.
It's never good to mulch right up to the bark of a shrub. You want to leave a little space. For trees, you want to make sure you don't cover the trunk flare and mulch up the trunk, or volcano mulch as we call it..
This is an example of volcano mulch. Volcano mulch is the practice of piling mulch high against the trunk of a tree. Personally I can't stand this look - maybe it's just because I know how bad it is for the tree. However this look became popular, it's a death sentence for a tree. Piling mulch this high keeps the bark damp. Remember how I said above that mulch helps to hold in moisture? Mulch up against the bark of a tree helps to hold in moisture. It also keeps the trunk of the tree too hot. Mulch decomposes over time and the process of decomposition creates heat. Moisture and heat creates the ideal environment for insects and disease.
So, wait. Why doesn't mulch cause harm to my plants in my beds? Because you don't put it on as thickly as you see in this pile here. It breaks down more slowly so it doesn't heat up as fast or as hot.
Let's get back to the volcano mulch. If you have a warm, moist environment that just is the perfect breeding ground for insects or disease. It will also soften the bark of your tree allowing insects and disease to get inside the vascular system of your tree. And finally, it causes the tree to rot from the outside in. In nature, when trees die, they die from the inside out.
Want to know the proper way to mulch a tree or shrub?
Here's an image of a properly mulched tree. Notice I put two light blue lines on either side of the tree that start a little further up and go straight down, parallel with the tree. Now look at the white arrows. Where the trunk "flares" from it's vertical pattern is called the "Trunk Flare". This is the natural base of the tree trunk. Notice how it's visible in the tree we mulched and absent in the trees that were volcano mulched in the photo above. The tree we mulched will continue to go on a and live a long, happy life with no compromises arising from the mulch. The trees in the photo above will likely be dead within a span of 5-7 years. Not only is this bad for the environment, but it's bad for your wallet.
When mulching your trees, leave the trunk flare. If you're not sure where the trunk flare is on your smaller trees, leave a little space between the mulch and the tree. You never want to mulch more than 3 inches. We re-mulch, or top-dress, our beds every year. This is to give it that new, pretty coating, but it's also because as I mentioned above mulch breaks down. After the initial 3 inches is down in a new bed, we go ahead and top dress with an inch or so every year. If you stick to around 3 inches, you don't have to worry too much about volcano mulch.
The same is true with your shrubs. You love them, but give them some breathing room. Don't hug them too tightly with mulch. Leave a little space - approximately a finger's width - between your shrubs and your mulch. If you use proper mulching techniques, you never have to worry about any detrimental issues arising from your mulch.