· Brent Wilson's Answer
· If your plants still look healthy, this could be signs of a little too much water. When tomato plants grow real fast in mild spring weather, the part of the plant above the ground often exceeds the development of the root system. Then, when the weather quickly becomes hot, the plant will try to compensate by reducing it's leaf area by rolling leaves. The leaves curl along the length of the leaf in an upward and inward fashion. It is often accompanied by a thickening of the leaf, giving it a leathery texture. If this is what your plant is doing, and you are now watering deeply every day, this is just a simple case of slight overwatering. If you cut back a little on the watering there shouldn't be anything to worry about. The plant should readjust within a week or so.
Too, it could just be leaf roll, or leaf curl. This is a physiologic distortion that may develop with periods of cool, rainy weather. It causes the lower leaves to roll upward and become thick and leathery. Leaf roll does not affect plant growth or fruit production and requires no treatment.
That being said, there are more serious problems that can cause the leaves to curl on tomato plants:
Check the underside of the leaves for bugs, specifically aphids. Aphids are small green insects. Infestation can cause leaves to yellow and curl. I doubt this is the problem but if you find aphids, whiteflies, or any other insects, spray with a product containing organic Neem oil.
Herbicides, such as 2,4-D can cause leaves to curl. But, since you're growing the plant on your deck, you probably haven't applied any weed killers near or around the roots of the plant?
There are also a few types of incurable viruses that can attack tomato plants. If the plant begins to really look sickly, with whole branches dying off, remove and discard the plant. It's definitely not too late to replant, but I would suggest sterilizing the container or using a different container. This is one reason I like to plant at least two tomato plants. If one gets a virus, it can quickly be removed and discarded. Then you still have one more plant left.
Hope this info helped.)