Ha, I intentionally PULL the ones out of the more wild area here because I don't want them to get away and become invasive. In central PA (I'm also in 6A) V. bonariensis self-seeds very readily. The butterflies love it though so I continue to let it grow here, pulling all the extras out every year. If I don't, I think it would totally take over and crowd out all of my other garden plants except maybe the coneflowers. I don't have any other garden plants here that seed so vigorously, and I have a lot of different kinds of plants since I've been butterfly gardening since 2005. V. bonariensis is the very first plant that I saw my first Giant Swallowtail nectaring on. It's a great plant to have for them in the garden, but I control its spread and limit it to my garden and ONLY in the section that has been allocated for it.

There were some hastata close by, and their flower spikes stay in a much tighter bunch and more erect. I suspect this could be Verbena x engelmannii, which is a natural hybrid of V. hastata and V. urticifolia. The only other verbena that I've seen around here is V. stricta. V. simplex and V. bracteata are also supposed to range in Illinois, but I haven't seen them locally. This plant could also be a cross of V. stricta and V. urticifolia. I guess I have to key it out to be sure. Apparently all these native Verbenas hybridize very easily and there's a named hybrid species for ever combination imaginable.

I've never been able to get verbena to look good for more than a month here in Colorado (zone 5b) either. The foliage always does that to me and I dislike it, so I end up cutting it out. I decided several years ago that there would be no more verbena here. I do love the way it looks but not when it does this.

oh yes, you're right about the irrigation – it has a rain monitor on it and the timing is much longer right now. I didn't explain that well. I have another one of these that is thriving, and these two are struggling and have had this issue for months now. I've cut back the impacted stems a few times.