Many trees such as female ash, Siberian elm, honeylocust, hawthorn, crabapple, maple and goldenrain tree may seed themselves in lawns. Dense turf and mowing to a 3-inch height should inhibit most tree seedlings. Lawns thinned from shade or poor cultural practices are more susceptible to weed invasion, including unwanted tree seedlings.
Aerate, fertilize and properly water the lawn to thicken it and make it more difficult for tree seedlings and other weeds to establish. Trees such as aspen, sumac, plum and Schubert chokecherry may appear as though they reseed themselves in the lawn. Instead these species produce suckers, which are shoots arising from the lower stem or roots of the tree. They should not be confused with seedlings, which form from seeds. A product such as SuckerStopper RTU™ may be effective for controlling tree suckers.
For more information, see the following Colorado State University Extension fact sheet(s).
For more information, see the following Planttalk Colorado™ script(s).