Hesperis, Dame's Rocket, Sweet Rocket 'Alba'

This pretty perennial self-sows aggressively and persistently in the garden, and can crowd out other more desirable garden plants if not ...Read Moreregularly thinned. It can spread rapidly. The seeds can lie dormant in the soil for many years, only to sprout when conditions are right. Once you've let it go to seed, removing it requires a great deal of work over many years, even if you catch it before it's spread to neighboring properties. It's been five years, and I'm still trying, but it's wearing me down.

Though it isn't a North American wildflower, it is often included in cheap "wildflower" seed mixes here. It's a threat to wild habitat over most of the continent except the deep south.

Garden phlox (Phlox paniculata) and meadow phlox (P. maculata) have similar garden qualities (including fragrance) but are harmless. Money plant/honesty (Lunaria) is also similar and seems not to be invasive.

Driving across New York State on I90, I observed with mixed feelings how many shady moist wild areas had been taken over by this plant. The color was pretty, but it reminded me of purple loosestrife and the similar widespread destruction of habitat wrought by that seductively colorful intruder...

This species is prohibited or declared a noxious weed in three states, and both the US Forest Service and the National Park Service are asking people not to plant it:
http://na.fs.fed.us/spfo/invasiveplants/factsheets/pdf/dames...
http://www.nps.gov/plants/alien/pubs/midatlantic/hema.htm

This plant was given to me years ago by a friend who had it on his property. It has been banned(!) in CT and Mass. by the plant nativists...Read More because if is not a "Native". It came to this country centuries ago from Europe, brought by our ancestors. It is a lovely thing coming in all colors of white, pinks, fuchsia/rose and lavender. It blooms when most other plants have not begun to to flower - bridging the late bulbs, peonies and irises in my garden. Yes it does self-sow, just as do other plants that we cherish, but it certainly is NOT invasive, and if there are too many in your borders, simply pull them out! It does not propagate by underground roots, and does not seed itself far from the original location. If you do not want it to spread, simply cut it back after blooming and before it goes to seed. In short, it is a delight and an ornament to the world. If one wishes to discuss horrid invasive plants, then Garlic Mustard is THE real pest, and this biennial is the scourge of my part of CT.

This plant is Prohibited in Massachusetts and Banned in Connecticut.

This plant grows wild in roadside ditches and is spectacular when blooming.. In my gardens I allow a few to remain to self-seed wherever...Read More it wants, but pull most of the plants out after the first flush of bloom. This way I always have young vigorous plants which do not take up too much space and space where I pull them out to plant other new late arriving perennials. Plants if left from year to year get very large and take up a lot of space with unattractive leaf growth. It survives extreme cold and/or dryness.