Q. I have a number of hackberry trees around my house. They are not very attractive but they're all I have right now for greenery, shade, bird habitat, etc. Most of them have bunches of stems that grow up from the base of the tree. Cutting them off is a temporary solution and seems to stimulate their growth. Is there any way to stop this without damaging the rest of the tree? Thanks,
---Beverly; near Waco, Texas
Q. I have a beautiful plum tree in my backyard and a ton of suckers coming up from the outstretched roots of the tree. How can I safely keep them from coming up, and what is a good way of getting rid of them without harming the tree or pets? Right now the suckers get mowed off, but in between mowings they come up like wildfire.
---"Banana Boat"(J. W.) in Damascus
A. My first call in an attempt to answer this frequently asked question was to "The Pruning Book" author Lee Reich, who continued under protest after I read him the questions. "Beverly near Waco"—Lee has a bone to pick with you!
"Hackberry is one of my favorite trees!" bellowed our impassioned pruning expert. "It has beautiful bark, fruit for wildlife…!" Once we calmed him down, Lee offered some tips on dealing with suckers.
"If it's a tree growing on its own roots and not a grafted tree, you can sever the suckers from the tree with a shovel and they might develop roots." Heck, some of these suckers might already have roots, says Lee, who points out that these seedlings will grow into the exact same kind of tree. So you two don't have a problem, you have free nursery stock!
However, if it is a grafted tree, it's the rootstock, and not the variety up top that you're deliberately growing that's sending up its unwanted shoots from below, says Lee. "Try and pull these shoots off as opposed to cutting them if you possibly can"; he instructs. "If not, just keep pruning or mowing them.
Oh and I'll bet that "plum tree" in Damascus—which I think might be Damascus, Maryland and not the other one—is a purple leaf plum, of which the book warns: "Trees spread by suckering. Plant where you can control sucker growth through mowing or pruning." In other words, some trees are notorious for doing this. Especially in Damascus.
Lee adds that although many people use the terms interchangeably, 'sucker' generally refers to what our listeners are dealing with: Straight up shoots that appears from below the soil. 'Water sprouts' are a similar problem, but these shoots grow straight up out of an existing lateral branch. Lee says to "pull those off as soon as they appear; don't cut or prune them off. You want to snap off the 'whorl' at the base or it will grow right back."
"Both suckers and water sprouts are a sign of excessive vigor—and that 'vigor' is taking energy from the other parts of the tree," explains Lee, who adds that your options beyond pulling off offending water sprouts are:
- • Use one to make a new central leader. That's right—if a straight-up shoot is coming off a branch near the top, it's the right tree for this kind of thing, and you need a new central leader (because say, the old one was damaged by an ice storm or something), you could train this shoot to take over.
• Bend them so they grow horizontal; use weights or string to hold them in place. A vertical branch made lateral will stop making extra demands on the tree, and produce more flowers and fruit (provided it's on the kind of tree that could do so to begin with, of course). Lee says to make it a straight line; another water sprout will take off if it forms an arch.
And he was! The Ohio State University Professor Emertis agreed with Lee about water sprouts in trees: "Absolutely pull them off if you can reach them; if you prune them, they're like the hydra—they'll re-grow 3 or 4 more in their place. And the sooner and younger you pull them off the less likely the chance they'll re-grow."
And those underground suckers our listeners are bedeviled by?
Dr. Ferree's specialty is apple trees, which may be why Lee us pointed to him. Turns out that some apple orchards he studied were thrilled to get their trees down to an average of 18 suckers each a year; because they had started out with 300 per tree! Apples must do this a lot, huh? "Oh yes," he says, "and the rootstock is often key. As you know, the desired apple variety is always grafted onto a rootstock of another variety, and certain rootstocks, like "Malling 7" are notorious for suckering, while others, like "Malling 26" almost never sends up suckers.
"We see the problem worst in plants that are rooted too shallowly. Being that close to the surface seems to encourage this kind of activity. So if you have lots of suckers, add a layer of topsoil or compost over the area and it may make things better. Also, if you can excavate an area that has a lot of suckers without harming the tree, you may see that a single root is sprouting almost all of them. Prune that root off and the suckers may go with it."