Pollination occurs naturally outdoors, where wind and insects carry pollen from one flower to another to fertilise them and set fruit. Tunnels and glasshouses shelter plants from wind, and fewer insects go inside so natural pollination is sometimes not enough to set a full crop of fruit. Incomplete pollination of a flower can produce a fruit that only develops and grows on one side while the other side remains hard and misshapen. This can be a problem with strawberries. Peaches, nectarines, grapes, melons and aubergines among others can yield better with help.
Hand-pollination is the answer. When the first flowers are just fully open and conditions are dry, brush over the flowers gently with a very soft brush or a little cotton wool. In the past gardeners used rabbits’ tails, but animal welfare was not a consideration then. Paintbrushes are a bit too stiff for pollination, but the likes of a camera lens brush is perfect. Never use one on a lens afterwards, because it picks up oils from pollen that would smear the lens. Pollen grains have spines for gripping onto hairs such as on bees’ bodies, and they brush off onto the sticky stigmata of other flowers – job done. It is best to repeat for a few days running to ensure good pollination and catch the later flowers. Tomatoes are easy to pollinate by vibration; tap on the flower trusses or the supporting canes or wires, or water them from above with a coarse spray of water.