Suckers Suckers

Backyard Wisdom, October/November 2017

by: Gilbert A Smith, ISA Board Certified Master Arborist

Indiscriminate sucker growth on the trunk of a Bi-colored Oak. photos by Lesley Bruce Smith

Sixty years ago when I was a young sprout, my mother taught me to remove all of the little shoots that came up around the base of our French Hybrid Lilac so it would flower well. The lesson from her was that suckers “sucked” the “juice” out of the Lilac. Many old fashioned landscapers still do this.  

When I was being trained as an arborist fifty years ago I was taught to remove all the suckers from the root crown, trunk and branches of the trees because I was taught it is healthier for the tree and that it looked better.

Suckers at the base of a struggling Linden tree

Forty years ago at the University of Illinois, I learned that we must refer to shoots that come up at the base of the tree as suckers, while those shoots that arise on the trunk and branches must be called water shoots/sprouts. For the sake of simplicity I hope you don’t mind my referring to both kinds as suckers. I was also taught that suckers arise as a result of grafting, intense hybridizing or drastic trimming. In other words, they are a survival mechanism, sending out shoots when the tree is stressed. You may have noticed that the harder you cut a tree or shrub, the more sucker growth you get; it’s as if the plant is telling you “You’re cutting me too hard…so stop it!”

About thirty years ago, the International Society of Arboriculture finally did research about the removal of suckers from tree trunks. Contrary to all of our long held beliefs, they discovered that when suckers are removed, it actually makes trunks and branches weaker. We shouldn’t be surprised as to why this is: because trees get their food from the sun through their leaves. Suckers are the trees attempt to get food when their supply has been cut off. That is why all of our beautiful Ash trees suckered like crazy at the base when the Emerald Ash Borer killed their branches.

So the good news is that you don’t need to stress about getting all those suckers off your trees. Listed here are the reasons we cut suckers in a discriminant manner:

  •  We still recommend thinning or removing some suckers if they are running into adjacent horizontal branches (suckers tend to grow straight up and hit healthy scaffold branches).
  •  We thin suckers if they're too thick, because they limit air circulation within the tree crown which promotes fungal and bacterial infections. And while we’re talking about bacterial infections we need to underline that any trimming tools should be sterilized to prevent spreading the serious disease called Fire Blight not only when you are trimming suckers but when you're doing any tree or shrub trimming.
  •  The final reason we recommend sucker removal is if they arise below the graft. Most of our ornamental trees are grafted onto a hardier root stock and if the root stock is allowed to grow, it will overgrow and kill the lovely ornamental tree that it is grafted onto. Currently many trees are grafted onto their own root stock but we still regularly see Apple trees sprouting up where a dwarf Crab tree was planted.

I bet you didn’t think I could talk so long about a simple thing like suckers. My object was to simplify and de-stress you about a common misconception. If you’d like some diagrams on how easy it is to maintain your trees, request our Arborsmith™ Abstracts on Ornamental Trimming and Tree Trimming.

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