I have an old Black Knight that is sited in my front garden near the driveway and street growing under pretty challenging conditions - full sun, dry sandy-ish soil, exposed to severe northwest winter winds. The thing is doing great! I am very pleased with how this particular cultivar performs as we are close to the borderline of hardiness for Buddleia in our zone and this is not a sheltered location at all. The Black Knight grows about 7 feet tall each season, which is tall enough as it is - can't imagine how large it would grow if it wasn't cut back. I cut it down sometime in April when the new shoots appear from the old wood. Just above the green buds so it's about 12-16" high. I also thin out some of the weaker or dead stems and maybe even remove some of the shoots. Btw, I also have a Pink Delight which is not as vigorous so I don't usually cut that one down as low as the Black Knight. Here's what it looks like this Spring after it got its pruning -

I'd advise not cutting it back. Just wrap the netting around the Fothergilla and attach to the Buddleia as well. The deer are not going to duck under the Buddleia to get to the fothergilla. They can't see the black netting, and feeling it but not knowing exactly where it is is very unpleasant to them since they can't tell whether they might get caught up in it.

I have been rooting butterfly bushes for several years(i've moved twice) and I never do anything more complicated than sticking the stems in potting soil. I take about a 5" piece, strip all but the top two sets of leaves, and plunk it in a 4" pot of pot. soil. If it is a bit flimsy, I'll poke a hole with a stick first. I keep the soil moist and pinch out any flowers that try to come for a few months. Looking back in my gardening journal, in 2005 I took 4 cuttings from my blue and 6 from my white on June 23rd and had visible roots at the bottom of the pot on July 11th. I've done this with abelia, spirea, gardenia, oakleaf hydrangea, and hardy verbenas. I'll repot them in progressively larger pots once or twice and then in the ground they go. Mere

Oasis is floral foam that has been described in recent posts as a rooting medium. I wish I knew how to post a link to the thread but if you search for "Ladysmith" who was the original poster, you can get all the info needed to try this method. I started lavender, butterfly bush, verbena, salvia, hydrangea, sage and a few others about 3 weeks ago, and I have been potting the little plants up, cubes and all, as I see roots coming out of the floral foam. I just cut the foam in about 1 inch cubes, soaked them until they were wet, drained off any excess water, poked a little hole in the top, and dipped the cuttings in rooting hormone. I put them in a plastic tray in my bathroom window (biggest window sill in the whole house!) and every time the cubes got light green (the color of oasis when its dry) I'd add more water and drain off any water that didn't get absorbed. Of course, my DH wants to know what I plan on doing with all these little plants because I think he wants his bathroom back!