Last year I bought a patio apple tree (malus grenadier ) which was in flower at the time and in September had 4 cooking apples. This year I have had no flowers or fruit, although the plant is still growing and has thrown out new leaves. It has been fed and with the rain this summer has been well watered. Any suggestions as to how I can get fruit from it next year, the label on the plant says--self fertile, heavy cropper.
About this time of year trim the new growth back by about a third. This will encourage the branches to develop fruiting buds for next year. In September give the tree a couple of handfuls of potash, this also encorages fruit. Grenadier is one that I grow and I enjoy it as a cooker and also as an eating apple as the fruit matures.
Yes garden stores will have the potash. If you can find an allotment society near to you you will also be able to buy it there. You don't have to have an allotment to belong to many of these and once a member can save quite a bit on garden supplies.