Rembember if you cut below the 'Y' the plant will need to 'Y' again before they bloom. If these were my plants I would just leave alone, spray and feed the on a regular bases. See how they go the first year and adjust they care as you learn about them.

The best place to prune a brugmansia is above the Y. It will have to grow less next year before it starts producing flower. But since a brugmansia produces blooms on new wood it will have to grow a new Y before it can start blooming next year. Mine died to the potting soil last year and that may not have been all bad. I had 2 trunks last year and it had 4 trunks this year which looked pretty perfect. I took some tip cuttings. This is a variegated plant which I guess is even more likely to rot and greenwood is more difficult anyway. So I am using chopped sphagnum moss and Turface, equal parts as a starting media and putting the cuttings in a covered pot together. If that doesn't work starting in water works for a lot of people. I don't like the long transition to soil. I think these plants might be water hogs. Last year this plant was in a different garden with an eastern exposure and was misted each morning. I had lots of leaves and if a worm ate a hole I just pruned off the leaf and a small leaf grew big to cover the spot in a few days. This summer it got plenty of water but no misting and the trunk did not re-grow it's leaves. It's a beautiful plant either way. As a multi branched tree there is room for bellowing Diamond Frost euphorbia and calibrachoa. Begonias are so easy to start I think I will just start over next year with the cuttings I took.

I myself just started growing brugmansias...I bought some cuttings online ($1 a piece) late summer last year and very fortunate enough to see a couple of them bloom. Bought another batch in the fall but lost a couple of them (left them out too late) and bought more online 2 weeks ago (10 pcs. for $10 plus $5 shipping)--all 10 are now rooting very well in water inside the house. I am in Port Orchard, WA. Http://www.ebay.com/itm/Angel-Trumpet-Brugmansia-Pink-10-UNROOTED-Cuttings-/332164919599?hash=item4d5692712f:g:LPAAAOSwOgdYrLKF

I never cut anything back until the spring. I live in zone 4 and we have very cold weather and snow. Leaving the dead flower stalks and plants catches the snow and piles it around the plant. That helps protect the roots. If I cut them back the wind would whiz the snow across my flower beds and pile it where it does no good for my plants. This works for all plants that die back in winter. I wait until my plants start to show new growth and then begin my cleanup