Traditional garden folklore suggests that Good Friday, the Friday before Easter Sunday, is the best time to plant potatoes and there are a number of reasons why.
According to the folklore, plants grow better and bear more fruit when planted on Good Friday. This appears to have been an idea started in the 1600s when potatoes were just arriving in Europe and people were concerned the tubers might be evil. In order to protect themselves from the evil of potatoes, people began planting them on Good Friday after sprinkling the soil with Holy Water so that the devil could not blight the precious tatties.
Others suggest that it was simply the first day when ordinary working men could get a clear day off work to get the job done, or because temperatures are generally still cool but the soil is soft enough to cultivate.
Easter is also the last lunar festival in the Christian calendar, which is why it moves about from year to year. If you believe in gardening by the the moon, it just so happens that Good Friday is always a good day for planting root vegetables.
Certainly, there is no scientific evidence that planting on Good Friday makes seed potatoes grow better, given the fact that the date changes from year to year with Easter falling anywhere between mid-March and mid-April each year.
The differences between climates in different regions may mean that Good Friday might not be the best time to plant potatoes in your area. Potatoes usually can be planted safely two to three weeks before the last expected frost so that is a good way to gauge the optimum time where you live.