How to Kill Thorns & Weeds in Existing Flower Beds

Hand-weed the site by using a small shovel or similar tool and digging under the unwanted vegetation's roots. Simply pulling on the weed or thorn isn't enough, as it will still grow if its roots remain intact and in the ground. Once you are under the root, pull on the weed or thorn to get it out of the ground. Eliminating the entire root ball prevents the weed or thorn from popping up again.

Use a herbicide formulated specifically for the type of weed present, and spray it on the weed. For example, knockweed, quackgrass and spurges typically respond well to post-emergent herbicides. Apply the herbicide directly to the weed or thorn and take care not to disturb your flowers in the process, as it could cause them harm. If you're not sure what type of weed has invaded your garden, take a sample of it to a nursery for assistance.

Pour boiling water over the weed or thorn, if it is away from your other plants. The boiling water burns the vegetation, causing it to die. However, the water can also cause your flowers die as well, so only perform this action on weeds and thorns that are away from other plants, such as on the border of your flower bed or in spaces between the plants. This method is an effective alternative for those who want to avoid the use of herbicides.