Don't need to stake potatoes,when they look like they are dying they are ready to lift.
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prune

Potatoes need a tremendous amount of water to produce a good crop. In pots you should be watering at least once a day. Don't worry about the top growth falling over it won't affect the potatoes underneath. "Earlies" should be ready to harvest about now but they don't store very well so only take as much as you can eat in one meal. Main crop potatoes should take around 17 weeks from planting to harvest and should be ready in about 4 - 6 weeks time depending when you planted them. If you want to find out how big they are you can dig around with your fingers until you can feel the tubers. This way if they aren't ready then you can simply replace the soil and they will continue to grow!

Thanks for the replies. Watering I have done,I will be "harvesting" the earlies this weekend so we shall see. I have just never seen so much top growth before when I have grown potatoes in pots. But thanks to those whoanswered my question.
Cheers