Tomato leaf problems - help
My greenhouse tomatoes, which were doing well, are now suffering. This started off in the form of curling leaves, which then developed mottled brown patches and are now turning yellow. Some of the yellow leaves are becoming floppy and mould like in small patches. This is working its way up from the bottom of the plants. The plants are all in individual deep 40cm containers (with drainage holes) buried in the ground (solid sandstone) to give depth. They are approx 3 feet tall, have 2 or more sets, and are developing a good crop of fruit, but the leaf problem will soon be up to their level. I have a cucumber plant growing in a similar pot, next to the tomatoes, in perfect health. My greenhouse was thoroughly cleaned with Jeyes fluid (and a sulphar candl) before I planted anything in it. It is only a small (8ft x 6ft) but it is well vented - 2 automatic roof vents, plus a louvred lower vent and of course a door. I make sure that the latter two are always open during the day. According to the max/ min thermometer, the inside temp has never dropped below 50 degrees F. I feed them once a week with a Tomorite mix, but do water them twice daily (less than a mug full for each plant). This is only my second year using a greenhouse (and I'm still new to gardening in general), and I have tried to follow all the best advice I can find, but I'm at a loss to know what the problem(s) is and how to cure / prevent it in future. I also find giving tomatoes the correct amount of water mind boggling. How can you tell how much is the right amount? How can I insert pictures of the problematic leaves into this missive? Please help?