When trees are stressed or have suffered some sort of trauma, they often respond by producing upright shoots called water sprouts and suckers. By most definitions, water sprouts are shoots that develop on the trunk and branches of trees, while suckers are shoots that grow from roots or the base of a tree. Water sprouts and suckers grow from dormant buds in the bark and are weakly attached to trees unless they’ve been allowed to grow for many years. They are both problematic because they can crowd the canopy of trees, reduce flowering and fruiting, alter plant structure, make trees more susceptible to wind and ice damage and ultimately look unsightly.
Water Sprouts on Trees
Water sprouts occur due to stress or injury from storm damage, root loss, soil compaction, topping, disease, over-pruning or drought. Determining the cause of the sprouting and fixing it is the key to keeping water sprouts from returning. Simply removing them all without correcting the underlying issue will usually result in sprouts promptly growing back. If you have a tree with many water sprouts, the best approach is usually to leave some of them because sprouts can help a tree rebuild its energy reserves.
Water sprouts can be thinned so that they are spaced apart and grow away from the trunk and permanent branches. Keep in mind, if too many sprouts are cut off at once they will grow back. Shortening water sprouts is another option that will keep shoots from getting too long and will slow their growth and regeneration. Shortened water sprouts may also be pruned into strong limbs over several seasons to replace weak limbs in the crown of the tree.
Some tree species naturally produce more water sprouts than others. Crabapples, oaks, maples and dogwoods will frequently develop numerous water sprouts in their crowns and require regular pruning to create and maintain good structure.
Suckers on Trees
Similar to water sprouts, suckers can be a sign of stress in a tree. If they are allowed to grow they can form multiple trunks or grow up into the lower parts of a tree. On grafted trees, suckers can be a symptom of partial incompatibility between the rootstock and scion if the two aren’t perfectly matched for size or variety. Suckers that grow from below a graft union will usually have a completely different appearance from the variety of the main stem and may outgrow the desired variety unless they are removed. Additionally, suckers can be the consequence of an injury to the base of the tree trunk from lawn mowers and string trimmers, or significant injury to the crown of the tree.
Unlike water sprouts, suckers should be removed as soon as they appear. Once suckers start developing on a tree they will usually continue to occur for the rest of that tree’s life and will need to be removed regularly. Suckers that grow up in lawns are easy to manage with a lawn mower; those that grow from the base of the trunk or from roots in landscape beds will need to be removed by hand. Ideally, they should be cut back to the point where they emerge from a root or the stem, as leaving a stub can make the problem worse by causing multiple shoots to form. Removing suckers that arise from roots may require a little digging.
There are products for sale that contain synthetic auxins (NAA) that are labelled to control sprouts on certain trees. Unfortunately, little research has been conducted on their effectiveness on landscape trees. Similarly, some herbicides have been shown to be effective at controlling and suppressing suckers, but they are not recommended for use on ornamental plants. Herbicides applied to suckers have the potential to harm the parent plant.
In conclusion, the best way to prevent water sprouts and suckers on trees is to keep the trees as healthy as possible with proper culture and pruning. If your trees already have lots of sprouts, do your best to figure out what is causing them stress, and do your best to correct it.
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