What time of year can you cut back a bottle brush tree?
We don't know for sure what species you have or where you live. I'm also wondering if you are talking about some corrective pruning or rejuvenating pruning (cutting at ground level in the expectation of vigorous regrowth). But, for general pruning...
1. Just about any time you have your pruners handy.
2. Major pruning in late summer/early fall may result in winter damage to tender new growth.
3. Pruning prior to flowering may result in less visual appeal for that year.
as to number three .. stated another way ...
if you want to enjoy the flower show.. prune immediately after bloom ... if you dont care.. whenever ...
now.. we need an ID.. isnt there a shrub under that name.. and a chestnut/buckeye tree ... that is the failure of common names ...
in defining that.. we can give better instructions
I assumed the OP was talking about some type of Callistemon species, but maybe there are also other possibilities.
I was thinking Aesculus parviflora, like Ken. Need an ID.
Mildly off topic....giggling: I just finished reading about and looking at wonderful photos of "bottle trees" from all around the world. (NE Forum) For a moment I thought the question was about cutting back a "Bottle Tree".
Over an hour on Gardenweb makes me goofy.