If you want to plant some potato tubers in March or April it is best to buy them in February and chit them first.
To chit potatoes it means to encourage them to produce shoots which, when planted, will grow to form the leafy stems above ground. Ideally place the tubers in a seed tray or egg boxes with the eyes (buds on the tubers) uppermost. Put in a greenhouse, shed or garage with a window but it must be frost free. You want the tubers to grow short, green stumpy shoots rather than elongated, white, weak shoots. To achieve this the tubers need plenty light and not be too warm.