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IN THE GARDEN: Best to leave space between tree and mulch to reduce chance of opportunistic pests

by Janet B. Carson June 18, 2022 at 1:31 a.m.
Piling a cone of mulch around the base of a tree, called volcano mulching, invites insects and diseases to attack. (Special to the Democrat-Gazette/Janet B. Carson)

Q: Everywhere around Northwest Arkansas I see mulch deposited up against the base of trees. As you know, the fungi, bacteria and critters in the mulch will assault the trees' bark and leave them vulnerable to pests and disease. Please use your platform to make homeowners and landscape maintenance firms aware that they are hurting, not helping. Also, it is not uncommon to see soil deposited over tree roots in which annuals have been planted. As you know, soil over tree roots should be limited to 2 inches so that roots can get the oxygen they need. Trees are an investment by landowners and nature, and we don't want to have to replace them. Thank you for all of the helpful information in your column.

A: Well said. Volcano mulching is not beneficial to the tree. A 2- to 3-inch layer of mulch with a bit of space left at the base of the tree is best. I call volcano mulch the bed and breakfast for rodents. They have a nice moist, warm place to live and the tree bark to feed on. A few pockets of soil under trees to plant annuals or perennials usually is not a problem unless it is widespread and deep. How much soil can be added over the tree roots also varies greatly by tree species, and type and volume of soil.

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Q: This past winter I lost many perennials that I had had for years, or, while not totally losing the whole plant, I had many that returned with reduced vigor. Because I was not able to mulch my beds all last spring, and because I was sick of dealing with a plethora of weeds, I covered my beds with unchopped oak leaves in the fall. This did help with the spring weed production, but could that be the reason for my perennial loss, or was there something about last year's winter that was the cause? I don't want to repeat whatever mistake I made. Can you help me?

A: A heavy layer of whole leaves can smother out weeds but can also damage perennials. You say you did this in the fall, so I am assuming your perennials had not gone totally dormant when you mulched them. We had a particularly mild fall and early winter, without a killing frost until January. If the plants had been fully dormant, they would not have suffered so much damage. Shredded leaves don't pack down as much as whole leaves, and the shreds allow oxygen through a bit easier. We did see some damage this past winter from the late freeze on tender new growth, but not widespread problems.


Q: Can you tell me the name of this weed? [The reader sent a photo.] It popped up in my yard along with those wild violets. I was able to pull some out easily due to the rain, but I have so many I was wondering if there is a weed killer that would destroy them and the violets without damaging the lawn.

A: I think your weed is annual bluegrass, a cool-season plant that is on its way out -- especially with this heat. The reason it pulled out so easily is that it is a winter annual weed that germinates in the fall, grows during the cool months, sets seeds and dies with the heat. The seeds on your grass are falling off now to come back and haunt you next season, but there is no call for herbicides now.

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Q: I want to plant a vitex tree. Is now a good time, or should I wait until fall?

A: Fall would be easier on you and the vitex tree, but if you are willing to water religiously, you can plant now. The smaller the plant, the easier the transition, especially when it is hot.

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Q: My Japanese maple has a number of dead branches (see photos of dead and healthy growth). Is there anything I can do to preserve the tree?

A: For now, prune out all of the dead branches. We are heading into some pretty hot and possibly dry weather, so water well. I would not do a lot of corrective pruning, other than dead-wooding in the middle of summer. Assess how the tree looks next spring as it leafs out; then you can selectively prune to buds that are facing in the direction where you want new limbs. Unless you continue to lose branches, you should be able to restructure the tree over time.

Retired after 38 years with the University of Arkansas Cooperative Extension Service, Janet Carson ranks among Arkansas' best known horticulture experts. Her blog is at arkansasonline.com/planitjanet. Write to her at P.O. Box 2221, Little Rock, AR 72203 or email jcarson@arkansasonline.com

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