By Tommygran
United Kingdom 
Every year my tomatoes split. I follow instructions regarding feeding. I mulch the ground and keep a very limited water supply going all day. I ensure there is a flow of air using roof ventilation and louver slats at the base of the greenhouse. I grow my plants from seed(gardeners delight). I only select the best plants to grow on. I don't overcrowd. I transfer seedlings to plant pots before planting directly in the soil. Each year I dig out the soil and prepare afresh using a mixture of soil and horse manure. Every year I also get tomato blight. I always burn plants at the end of the season.
1.What am I doing wrong?
2.Can I spray my plants to prevent blight?
Please help the season always starts so well and then ends in such disappointment.
1 Sep, 2014
Answers
I used to have this problem along with black spots on the base of the tomato. I felt that I was preparing the plant well just as you are but now I stand my pots of tomatoes in my shaded greenhouse in a trough that I never let dry out. During the hot weather 3 plants have been having a watering can filled with water from my butts every day and I feed them weekly directly into the pot once a week. I have had great crops ever since.
1 Sep, 2014
Not had it on tomatoes, just potatoes, but found this video - worth a try?
://www.youtube.com/watch?v=UxeBz1e2OwU
1 Sep, 2014
Thank you all for your help. I do spray with a copper fungicide already but am wondering if I should spray in anticipation of the problem rather than after the event. I will certainly try a more controlled watering plan next season. Although I have good ventilation in my green house again maybe I need to pay attention to extreme high temperature and open the door sometimes.
4 Sep, 2014
Previous question
You've mentioned two problems - tomato split and blight. You can't do much about avoiding blight, there's no pre treatment now that will stop it happening - it comes when it comes, and there's nowt you can do about that. UPDATE: Mancozeb or a copper based fungicide was once used as a preventive treatment, particularly in damp weather, and having just checked, Bayer does still make a copper fungicide, might be worth trying that, since you have a problem most years. Otherwise, its growing them under glass, where they're less likely to get blight, though it can still happen in the greenhouse.
Tomato split, though, you can do something about most years. There are two causes of the skin splitting - the first is irregular watering. If the tomato fruit, which needs regular and copious amounts of water to grow and ripen, goes short of water at a particular point, when water arrives, it grows too quickly and the skin splits. The other cause is wildly fluctuating temperatures, so in a year where you may have a heatwave for a week, followed by a cold week, its more likely to happen, or if you have high day time temperatures but plunging night temperatures.
1 Sep, 2014