There are two types of tomatoes: cordon and bush. The other name for cordon tomatoes is "indeterminate", meaning they could grow on and on as long as the conditions allow, so these you have to prune. Do this by pinching out the side shoots that emerge between leaves and the main stem, and pinching out the main shoot when it has five to eight trusses – fruiting stems – of tomatoes. (Four or five trusses is best for cordon tomatoes grown in a pot.) Determinate, or bush, tomatoes can be left to do their own thing, no pruning necessary.
Our wet, humid conditions are manna for blight (Phytophthora infestans), a disease that starts with brown splodges on the edges of the leaves and then rapidly runs all the way down the stems and into the fruit, turning the whole plant to mush and leaving the tomatoes inedible. Blight is spread by spores that move on the wind, so outdoor-grown tomatoes are vulnerable, particularly bush tomatoes, whose dense leaf shape limits air circulation. If they get blight, they tend to go down very quickly.
One trick to beat blight is to plant early-fruiting varieties that have some resistance to the disease. Cordon tomatoes 'Mountain Magic' and 'Primabella' are both getting a lot of good press; I've always found the tiny fruit of 'Matt's Wild Cherry' reliable. Older varieties 'Lemon Drop' and stripy 'Tigerella' are said to have some blight resistance, too.
Whichever variety you choose, you need to cajole your plants into growing as quickly as possible. Right now, tomato plants should be flowering, so it's time to start feeding. I use homemade comfrey fertiliser and a small handful of seaweed pellets every four to six weeks. If you see roots appearing at the surface of the pot, top-dress with mulch or compost and keep watering.
Protected environments minimise the chance of blight spores reaching your plants. If you have a greenhouse, a sunny porch, a patio coldframe, polytunnel or a large enough cloche to protect your toms, use it. Spacing between plants is essential – at least 45cm apart outside if you can. Too close together and poor air circulation allows blight to run amok more quickly. If your tomatoes are in pots, put other plants (not potatoes, which also get blight) in between.
If one plant goes down, remove it immediately (never hold out in the hope that it will get better) and you may be able to save the others; or at least pick enough green fruit to make chutney. It's admittedly the booby prize for outdoor toms, but it's better than no prize at all.
