By Jolewis
United Kingdom 
We have a buddleia in a pot bought last year. It was in flower when we bought it. Unfortunately we didn't realise that it needed pruning backin March/April. It has grown and has several flower buds but they are not opening and the leaves have drooped very badly. On examining the leaves there is nothing visible i.e. Spider mite or fungus no holes just drooping leaves. There were a lot of yellow leaves which dropped off when touched but since feeding they have gone and just one or two remain at the bottom. Is this a problem with the rootball or something else?
23 Jul, 2015
Answers
Feed me! Feed me now!
You can get a few years out of a Buddleja in a pot, that is untilthey go really woody. I know you see them growing out of brick walls but in a pot they need a lot of water to thrive, watering every day it doesn't rain. And they are greedy feeders, tomato food every week if you want good blooms.
To prolong life in a pot root pruning works in spring if you can be bothered.
The new dwarf varieties outgrow their pots quite quickly too and won;t thrive without water and feed. And T&M's Buzz grow to nearly two metres once in the ground.
23 Jul, 2015
Previous question
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On the assumption your plant was Buddleia davidii, and not one of the newer, dwarf versions such as Buddleia 'Buzz', the problem is the pot. This variety puts on as much as 10 feet of growth in a season, even if cut down at the right time in March, so you can deduce that keeping it in a pot isn't really an option. It needs to be in the ground I'm afraid to give it sufficient room for the roots it wants to grow but can't.
23 Jul, 2015