Black-eyed Susans can spread via seeds and underground rhizomes. To prevent spreading, deadhead the flowers before they set seed. As to controlling the spreading of rhizomes, that is more difficult. As you may have found, if you don’t get every piece, chances are that section of rhizome (a modified stem) that is left will produce another plant. Here are suggestions from the Purdue Cooperative Extension as to how to combat this problem:
1) Provide a large area of mulch around the mother plant. Keep up with digging up any rhizomes that spread from that mother plant (several times each growing season).
2) Another option would be to replant the mother plant in a container (with drainage holes) and put the container in the ground, with the rim about 2 inches above the soil surface. Check periodically to make sure rhizomes do not escape the container. Every year or two, prune the roots to keep the plant confined in its container, or repot as needed.
3) A third option would be to insert a barrier (or collar) around the plant, such as a section of deep-walled bottomless pipe about 8 to 18 inches deep, to prevent rhizomes from spreading.
In the meantime, use a garden fork to expose current rhizomes and then gently remove them from the soil.
Black-eyed Susans can spread via seeds and underground rhizomes. To prevent spreading, deadhead the flowers before they set seed. As to controlling the spreading of rhizomes, that is more difficult. As you may have found, if you don’t get every piece, chances are that section of rhizome (a modified stem) that is left will produce another plant. Here are suggestions from the Purdue Cooperative Extension as to how to combat this problem:
1) Provide a large area of mulch around the mother plant. Keep up with digging up any rhizomes that spread from that mother plant (several times each growing season).
2) Another option would be to replant the mother plant in a container (with drainage holes) and put the container in the ground, with the rim about 2 inches above the soil surface. Check periodically to make sure rhizomes do not escape the container. Every year or two, prune the roots to keep the plant confined in its container, or repot as needed.
3) A third option would be to insert a barrier (or collar) around the plant, such as a section of deep-walled bottomless pipe about 8 to 18 inches deep, to prevent rhizomes from spreading.
In the meantime, use a garden fork to expose current rhizomes and then gently remove them from the soil.
Hope this helps!