Q Why didn’t my new tree dahlias fower?

Graham Cole, by email A

MATTHEW SAYS Getting tree dahlias to flower before the first frost is quite a challenge, as the UK summer isn’t usually long enough. It can happen, if autumn is warm and extended, after a good summer with lots of heat and rain. But often we just enjoy tree dahlias for their foliage and grand stature.

Crown gall can damage edibles, such as Brussels, and ornamentals