Cottonwood suckers are frustrating because they keep coming. The way you deal with them depends on one question: do you want to keep the tree? If you do, the answer is regular cutting. If the tree is already gone and the roots keep sprouting, you have more options.

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The short answer: if you are keeping the cottonwood, cut suckers off at their base, at or just below ground level, as soon as they appear and while they are under 6 to 12 inches tall, and repeat through the season. Do not spray herbicide or “sucker stopper” on them: a Colorado Master Gardener answer on Ask Extension warns that cottonwood roots are interconnected, so herbicide can move into the tree. If the cottonwood has been removed, Ask Extension suggests a triclopyr product labeled for cottonwood or poplar, sprayed on leafy sprouts, possibly over two seasons.

Why cottonwoods sucker so much

Suckers are vigorous upright stems that grow from the base of a tree or from its roots, sometimes feet away from the trunk, as Iowa State University Extension explains. Cottonwoods are especially prone. The Morton Arboretum notes eastern cottonwood produces suckers and aggressive roots, and that its roots are shallow. A Colorado Master Gardener response on Ask Extension describes suckering as very characteristic of cottonwoods because their root systems are vigorous and shallow.

Iowa State adds that damage to the base of a tree or its roots can promote suckering.

If you are keeping the tree: cut, don’t spray

Cut suckers at their origin

Iowa State’s guidance:

Use hand pruners as soon as suckers appear.
Pull back a little soil to find the point where the sucker starts, and clip it there.
Do this while the sucker is still less than 6 to 12 inches long.
Do not leave a stub. A stub left behind will resprout with multiple shoots and make the problem worse.

Time it well

Iowa State notes suckers grow most vigorously in spring. If there are only a few small suckers, waiting until early summer to cut can reduce vigorous regrowth, though some will still come back later in the season. Regular cutting through the growing season is the best way to keep them managed.

Do not use herbicide on suckers from a living tree

This is the key rule. Iowa State says never to use herbicides on suckers, because any herbicide, contact or systemic, is likely to damage or kill the tree. The Colorado Master Gardener answer explains why this matters so much with cottonwoods: the root system is interconnected, so herbicide moves into the existing tree.

Iowa State also does not recommend “sucker stopper” products, citing limited research, incomplete control and the potential to harm the tree. The Colorado answer notes the common growth-regulator product does not list Populus (cottonwoods, aspens and poplars) on its label as an effective treatment.

Digging is not a fix

The Colorado Master Gardener answer notes that digging out roots can harm the tree and will not solve the problem, because the tree will keep suckering elsewhere.

Suckers in a patio or path

For suckers pushing up between flagstones, the same answer suggests the only options are cutting them at ground level or switching to a more solid, slab-like surface that suckers cannot come through.

If the cottonwood is gone: stopping the roots

Removing the tree does not end the suckering right away. The Colorado answer says a cottonwood’s root system can stay alive for up to several years and keep suckering.

In this case herbicide becomes an option, because there is no tree left to protect. In a separate Ask Extension answer, an extension expert recommends:

A product containing triclopyr, which is selective to woody plants, rather than glyphosate, which kills everything it touches, including lawn.
Checking that cottonwood or poplar is listed on the label as a target, and following the label exactly.
Letting sprouts grow until they have several sets of leaves, then spraying before leaves start to change color in fall.
Repeating that year or the next for anything that comes back.
Not disturbing the roots until suckering stops, because disturbance stimulates more suckers.

The same expert says home remedies such as Epsom salt sprays will not kill the roots and can build up salts in the soil. After spraying, wait to pull dead sprouts until you have confirmed the root system is dead. It takes a few months for herbicide to move through the roots, so check whether sprouts leaf out again the next summer.

If you have other trees you want to keep close to the old cottonwood’s root zone, ask your county extension office before spraying, and follow every label precaution.

Living with a cottonwood

Iowa State is blunt: trees that form suckers will always have suckers, and regular removal is part of normal maintenance. The Morton Arboretum also notes eastern cottonwood is fast-growing, weak-wooded and brittle, highly susceptible to ice damage, and has roots prone to invading sewer pipes. If suckers are only one of several problems, it may be worth talking to a certified arborist about whether the tree suits its spot.

Sources

Managing Suckers on Fruit, Ornamental, and Shade Trees, Iowa State University Extension, Yard and Garden
How and when do I prune suckers from the base of my tree?, Iowa State University Extension, Yard and Garden
Cottonwood suckers (Colorado Master Gardener response), Ask Extension
Cottonwood sprouts all over my yard (Cooperative Extension response), Ask Extension
Eastern Cottonwood, The Morton Arboretum

Top photo: R. A. Nonenmacher, CC BY-SA 4.0, via Wikimedia Commons

How to Deal With Cottonwood Tree Suckers