Shears allow you to clear an area for planting! Most areas only require one chop with the shears but there are some larger areas that may require more. Each time you clear with shears you will earn a watering can. Shears can be crafted by Kumi using shear blades and tool handles, or purchased from the Garden Store with Garden Store Tokens.
To use any Shears you have you can either tap on an overgrown area and then select "clear" to prune. Alternately you can tap and drag a pair of Shears out to your Garden and any areas that are eligible for pruning will show a little attention notification icon over it.