By Jew
United Kingdom 
Foliage on my potato plants are growing rapidly now over 3ft high & resembling a garden hedge does that mean yield will be poor?
10 Jun, 2020
Answers
Once the potato stems flower, turn yellow and fall, it's time to harvest.
10 Jun, 2020
welcome to GoY,
have you been 'earthing' them up as they have been growing? if yes then you will get potatoes. if not then you need to. Do you know what earthing up is? This is where you bring soil up against the stem so over time they get buried with just the leaves open to the light.
the plants in the farmers fields round here do get to that sort of height so that is ok.
10 Jun, 2020