I would consult the clients and make sure they are informed. Knowing what they have could be a detriment maybe they'll ask you to replace those plants with something suitable.

I would echo nicethyme's advice. I would approach the client in a friendly manner, present them with printed information on the noxious weed list, and also present them with suggested plants to replace the bad ones. You also will need to explain that the plants have not exhibited invasive tendencies in your clinet's garden because you have been controlling them.

I think the key is to be very non-threatening and present it as a chance to educate them and improve their garden. You want to be sure that they don't think that you will turn them in to the "plant police" if they don't cooperate.

V.
(not kidding about the "plant police" - I once had to accept a ticket on behalf of my employer because they were selling purple loosestrife)

Thank you for your good advice. Most clients told me that they don't care and I can remove them. So, the problem is maybe me. Probably I can easily remove Myrtle Spurge (with gloves) or Bouncingbet. But, right now, the Purple Loosstrife is so gorgeous and I just stand there and keep admiring its showy flowers. I understand selling them is no-no and ticket worthy. Establishing themselves in a wide open space is alarming and we should eradicate as soon as we see them (right?). But could just people enjoying them in a private enclosed garden be excused from law? What kind of penalty do we get if "plant police" raid the garden?

Is the "private enclosed garden" completly encapsulated? If not: "A mature plant may have as many as thirty flowering stems capable of producing an estimated two to three million, minute seeds per year."

Patty

Whoops! I am so sorry! It's my mistake.

I thought this was a sincere request for advice and not someone trolling for a fight.

I'm leaving now - buh-bye.

I didn't take Patty's post as trolling for a fight by any means. The poster asked for opinions, and she responded with facts to illustrate how much of a problem this weed can be. I often joke that PL ruined my childhood. A large woodland creek and meadow used to be great for skating in winter, and was an outdoor natural history classroom all summer. Then PL hit, and within two years it became so clogged with the plant that it was unskatable and almost inaccesible by foot. I'd do what I could to persuade the homeowner to eliminate the invasives.

Purple loosestrife takes over wetlands in my region of the country. They are now experimenting by introducing beatles that eat it exclusively. That should be interesting.

The older I get, the more I speak out about invasives and other things I think can come back and bite you in the butt years down the road. I stopped carrying a lot of nursery stock I once sold gobs of. It's just the right thing to do, and when people ask for it, I give them my spiel why they should at least think about planting stuff like that. You can't convince some folks and you let them have the last word....... and usually hear from them years down the road and they grin and admit they should have listened to you.

If your client says it's OK to pull the danged loosestrife, I'd yank it in a heartbeat and burn the nasty stuff. There are lots of plants to give the same effect and don't do that amount of environmental harm. I find the more sophisticated my clients get with gardening, the less they just MUST HAVE undesirables.

Round-up accidents are a great way to get rid of icky plants, to be most effective do it in spring as the plants first emerge and coincide with a mulching so the annoying plant can be quickly buried.

The purple loosestrife is a non native invasive and a bad enough one that you don't want it around at all.
(unless you have Galerucella beetles in abuncance)

To replace the bloom consider Liatris spicata which has a similar color, bloom period and effect.
There might be a version of Anise hyssop that works but it self sows like crazy.