A: The likely culprit is weather damage, even if knowing the cause doesn’t help with the problem much.
Live oaks have a tendency to sucker up from ground level when the tree suffers damage. This is a survival mechanism, allowing the tree to continue to live even if the main trunk is too damaged to thrive, but it isn’t a desirable characteristic in the landscape. Nursery grown live oaks are grown using acorns from trees with less of a tendency to sucker, but the chance remains in the genetics of individual trees. Since most trees (including live oaks) haven’t had a great three year stretch between devastating winter storms and exceptionally hot summers, the sucker problems are worse than usual now. Not every live oak will sucker, but conditions are right for it to happen.
There are no good chemical controls for live oak suckers that will not injure the parent tree as well. Dig up small numbers of suckers below the soil line – they’ll be back eventually, but small numbers aren’t a huge nuisance.
Now, regarding the veritable carpets of suckers some of our customers have brought us pictures of lately… the answers are workarounds, not perfect solutions. In these cases, your choices are:
Remove the tree entirely – Obviously, not our favorite. A mature live oak is valuable. Additionally, removing the tree will lead to a battle with suckers coming up from distant root sections in the lawn, but these can generally be beaten down with broad-leafed weed killers and regular mowing. Grind out as big a hole around the original stump as possible if you do this.
Loads of digging and pruning – Mow off and prune and dig all the shoots. It’s tough work, but it will fix the problem for this season. You’ll be needing to do this every year, though.
Roll with it – Sometimes, you have so many live oak suckers that it almost looks like a ground cover bed. Asian jasmine looks much like the live oak sucker leaves. Plant a bed of Asian jasmine in the affected area and simply prune the bed with a hedge trimmer from time to time to keep it neat. Again, not perfect, but better than a wild looking forest of suckers.