With cherry varieties you should pick your first ripe tomatoes when they are flowering on the 6th truss; for larger-fruited types you’ll have to wait until the 9th truss flowers. You might get a new truss approximately every ten days, so if you plant in mid May with the first truss in flower, you might expect your first pick sometime in the first half of July for cherry tomatoes and about a month later for larger varieties. In the meantime, buy British-grown tomatoes for the best flavour.