Gardeners generally say not to plant out bedding until the end of May when there's little chance of frosts. However, I do break that rule most years by a couple of weeks but it depends on what part of the UK you live in anyway. I usually do my baskets up on 1st May and protect them at night if the forecast is cold.
What's on sale in supermarkets isn't an indicator of when they can be planted out and I think they get earlier with their sales of bedding plants, which is fine if you can protect them from frosts. Or maybe they get them on sale early so they can sell you another lot when the first lot die of frost damage. I would keep an eye on what your local garden centre has for sale although they are generally much less expensive in supermarkets.
Originally Posted by: Caz