Hi, a maple sapling has taken root in my backyard planter box. It was hidden by a large vine and I only noticed it this summer. Digging it out will be extremely difficult and I am hoping you have some advice on how to kill it by other means. The trunk is approximately 2.5 inches in diameter.
Thank you for contacting the Toronto Master Gardeners. As you already know, it is better to pull these tree seedlings as small saplings, but sometimes they are buried behind other plants or we just don’t have the time or energy to intervene. You mention that digging out the sapling is not an option; as a result, your best bet would be to cut the tree as close to the ground as possible by scraping away the soil to get as close as possible to the point of attachment to the roots. Depending on the type of tree, you may find that the sapling sends up water sprouts from lateral buds. If this is the case, cut or pull these sprouts as soon as they develop and do not allow them to become large.
By removing the sprouts as they form, you are preventing them from developing enough to photosynthesize and to begin storing food reserves in the roots. Each time the sprouts form, food reserves must be withdrawn from the roots. By allowing withdrawals but preventing the accumulation of the photosynthate into the food bank in the roots, you will bankrupt the root system and it will eventually die. Persistence is the key to ridding your planter box of this sapling.