Watermelon, melon, potatoes: how to choose so you are not cross at home

Watermelon

A ripe one feels heavy for its size, with a creamy-yellow ground spot, not white. Knock it: a deep dull note, not a ping. The stem is dry. Cut it — dark seeds, flesh not pale at the rind.

Melon

It smells at the blossom end, not of chemicals. The skin gives a little, it is not bruised. Too soft — it has gone. A netted cantaloupe should smell sweet even through the net.

Potatoes in Britain

• Maris Piper — nearly all-round: mash, roast, bake
• King Edward — floury, for mash and roasting
• Charlotte / salad — waxy, for salad and jacket, will not fall apart
• Red (Desiree) — holds in borscht and stew
• New spring potatoes — thin skins, boil whole, not for mash