If you are buying plants now, do make sure they have been “hardened off” and can go straight out into the garden. The plants may have been started off indoors/under glass and won’t be used to the ever changing weather outside and there’s always a risk of frost that might knock them for six too!
So just to make sure, leave the plants outside during the nice days and take them in at night so that seedlings become accustomed to the strong sunlight and varying weather so toughening them up a bit. Then in a few days they can be planted outside and if you’re still in doubt that there may be frost about, wrap some horticultural fleece (net curtains or newspapers) around them at night.
Also watch out for those slugs and snails, as they love those young plants too!
So keep em peeled (for cheap plant sales and the slugs and snails) as Shaw Taylor (RIP) used to say!