Perennial garden thugs crowd other perennials
Most perennial flowers are well behaved and stay where planted and don’t spread out and crowd other plants around them. However, there are some that are notorious for being thugs and crowding and sometimes crowding other desired perennials completely out of the garden.
Seed Spreading Delinquents
Some plants tend to be a problem mainly by seed spread. Some of these would include:
Achillia or yarrow
Viola or “Johnny-Jump-Up”
Big and little bluestem (native grass)
Canada anemone (native)
Golden rods (native)
The key to successfully keeping the seed spreader thugs is to “dead head” or pick off the spent flowers before the seed pods mature and spread the seeds. If done faithfully, the seed spreaders can be a welcome addition to a garden.
Plant thugs that spread mainly by underground stems called rhizomes:
Bell flowers (Campanula family)
Moneywort (commonly called “creeping Jenny”)
Buttercup family (Ranunculus family)
Mints (plants with square stems)
Creeping ground cover sedums
These thugs can be grown if contained. Planting between a sidewalk and a house foundation is an example of such containment.
Planting in an isolated container by themselves is an option.
The third option works in a mixed bed. A large, solid sided container 12 to 20 inches deep with bottom drainage can be buried with about 2 to 3 inches of the container above ground level. Plant the rhizome spreading plant in the container and the container should prevent the rhizomes from spreading into the surrounding garden. The large pots that trees and shrubs are sold in are ideal for barrier pots for the rhizome spreading garden thugs.
One last bit of advice is to never dig and bring home plants you might see on a trip out of the area. A plant that is well behaved in one environment may become a serious garden thug, and possibly worse if moved to a new, different environment. And once established, it may entail serious labor and expense to eradicate.
And always research new plants gotten in trades or through club plant sales. There are times that some serious weed problems have been be received through both methods.