I have to admit, I see fewer mulch volcanoes huddled against trees in public places. I think word has gotten around – at least with municipal workers – that trees can be damaged or killed by too much mulching. Between owners? I’m not so sure. Let’s take a look at the problem.
Tree bark is a wonderful material: no matter the weather, the bark protects your tree from rain, snow, cold or drought. But it is designed for above ground use only. Bury tree bark or cover it with mulch, and microorganisms will break it down and attack the green cambium layer under the bark.
The cambium layer is an active, growing layer of cells that produce the phloem and xylem tissue that transport necessary fluids and provide mechanical strength. If the cambium layer is destroyed, the tree will die, but not right away. Most experts say that if the cambium layer is compromised, it can take six to 10 years for a tree to decline and die. Early signs of the problem include tip dieback – upper branches losing their leaves – and earlier fall color than previously seen.
When mulching around a tree, you need to leave space between the tree trunk and the mulch. Some say, leave a donut hole around the tree. Four to 6 inches is good, depending on the size of the tree. The bigger the tree, the bigger the space. And even if you started with a gap without mulch around the tree, don’t assume there is still a gap. Will see. Gravity works 24/7, and rain and wind can move the mulch around a bit.
Don’t get me wrong: I’m not against mulching around trees. It performs two important functions. It keeps weeds away and keeps rambunctious guys away (usually) with weedkillers. No mulch? This guy with hearing protection and a raging trimmer can girdle your tree in the blink of an eye. And that would be as bad as letting the mulch slowly rot the bark.
By removing the bark mulch, you can save the tree. I removed the mulch and saw the damaged bark. But if the cambium still works, the tree can recover, and I’ve seen that too.
There is another way to compromise the cambium layer: cover the flare of the trunk with soil at planting time. Burying the part of the tree that should be above ground will cause a slow death.
Arboriculture is an industry. Americans buy hundreds of thousands of them every year. They are sold at home nurseries and big box stores, but often started in nurseries in warmer parts of the United States. Trees are often grown in fields, like corn, then lifted and potted to be sold at your local nursery.
If you ask how deep to plant your small tree, the most likely answer (from my informal survey of homeowners) is “Plant it as it is in the pot.” But that’s usually bad advice. The process of taking a field-grown tree and putting it in a plastic pot is not precise. Time is money, which is why trees are often planted in containers without regard to how deep in the field they grow. The trunk flare (that part that should be above ground) is often buried.
To recognize the flare of a tree trunk, step outside and look at a tree planted by Mother Nature. You will see at the base of a tree that there are aerial roots branching away from the tree and the base of the tree widens just above ground level. This wider part is the flare of the trunk and should be above the ground.
Before planting a tree, take your fingers and pull the soil from the trunk of the tree to the surface until you can see the trunk flare out. If the tree has been in the pot for a few years (often the case with large trees) and the flare has been covered, small roots have started to come out of the flare in the trunk and need to be cut.
Large trees for sale in nurseries have often been moved from their original pots or bags to larger ones. At this stage, soil is added and often covers the flare of the trunk. I planted trees from the nursery with four to six inches of soil on the flare of the trunk. By removing this, I saved the trees.
What should you do if you planted a tree without considering the splay of the trunk? Watch it carefully. If your tree trunk is as straight as a telephone pole on the ground surface, you need to dig. You need to expose the flare of the trunk.
I like to use a single prong hand tool called a CobraHead weeder (www.CobraHead.cm) to expose the trunk flare. I gently and slowly loosen the floor and pull it out with my hands. In fact, I use my fingers as much as possible, because I don’t want to damage the bark of the trunk flare. Once you see the flare, re-level the ground around the tree trunk. It’s not as scary a proposition as it sounds. You can do it.
Trees are our friends. It’s not enough to give them a hug once in a while (as I’ve been known to do, on occasion), you need to make sure they’re planted and cared for properly. So get out and watch yours. You may need to do some work the next hot day.
Henry Homeyer’s blog appears twice a week on gardening-guy.com. Write to him at PO Box 364, Cornish Flat, NH 03746. Please include a self-addressed, stamped envelope if you would like a reply by post. Or email henry.homeyer@comcast.net.
