For starters, your Wisteria will not be happy in a planter. This rampant climber needs plenty of space for its roots. The next thing to consider is the amount of water it will need to become established, and see to that requirement daily for a while after initial planting.
This plant is rather large to get established quickly, and very often, by buying a smaller plant which is faster to get going is a better option - and saves money into the bargain.
You need to check too for anything untoward regarding insects, or indeed insect larva under the soil.
Here in East Kent, we've had no rain now for ages, and all sorts of plants are showing signs of stress. Can you give some idea what area of the UK you are in ?