How to Kill Hostas
Grown for their attractive foliage and ability to thrive in the shade, hostas (Hosta spp.) are garden favorites in U.S. Department of Agriculture plant hardiness zones 3 through 9. Hostas are tough plants that easily thrive and spread. Because they are so resilient, they can sometimes persevere despite your attempts to eradicate them from the garden. To win the battle against hostas, you must be relentless in your efforts until they no longer resprout. Otherwise, in time, they may return with full vigor.
Dig around each hosta clump, digging about 8 to 10 inches into the soil. Go deeper if the roots run deeper than this. Lift the clump from the ground, shake off the soil ensuring you do not break off any roots, and discard.
Sift through the soil in the hole with your hands. Also sift through the soil 1 to 2 inches beyond the hole from which you dug to look for any other hosta roots left behind. Discard all hosta pieces as they can resprout if you leave them on the ground.
Dig out new shoots when they grow, digging until you find the end of the roots. Alternatively, spray new hosta shoots when they reach 4 to 6 inches tall with a ready-to-use glyphosate herbicide. Repeat until the hostas finally die.
Grow other plants after removing the hostas so they use the space, water and soil nutrients. This way, any remaining hosta roots are less likely to sprout. If the hostas do regrow and you use a herbicide, do not spray the other plants, because the herbicide will kill them.