Lets Bust a Few Myths About Tomato Leaf Curl

I had written a post a few years ago about tomato leaves curling up and it is the subject most searched for on my blog. A quick Internet search brings up hundreds of posts and photos of tomato leaf curl or leaf roll as some gardeners call it. I wanted to bust a few myths by my own experiments just to prove to myself that basic leaf curl is nothing to worry about, or something that you can not do much about. We are not talking about wilting leaves, but fairly healthy tomato leaves curling upwards.
This is only about indoor grown tomatoes and might be different for outdoor grown crops.

CLASSIC LEAF CURL ON TOMATO PLANTS NOTHING TO WORRY ABOUT

 
TOMATO LEAF CURL CAUSED BY TOO MUCH HEAT
This to me is the most logical reason for the curling of tomato leaves and what I presumed was the main cause. The plant gets too hot so compensates by curling it's leaves so they get less sun exposure and keeps the plant cooler. This does make so much sense, however I have been in the greenhouse on cooler days after hot sunny days with plenty of leaf curl and the leaves are still curled and continue to do so. It could be that once a leaf has curled it never goes back straight which seems to be the case sometimes.

TOMATO LEAF ROLL CAUSED BY OVER WATERING
This is a popular comment on many posts and I even watched a video about it from the USA, so I let my plants dry out slightly so they were definitely not over watered, this didn't make an ounce of difference, the leaf curl seemed to be exactly the same.

TOMATO LEAF CURL CAUSED BY LACK OF CERTAIN NUTRIENTS AND A STRAIN ON THE PLANTS

I have noticed that early in the season there are no signs of leaf curl, however, as the season progresses and the tomato plants are starting to produce fruit, then the leaf curl seems to get worse as the weight of the crop increases. On the oldest leaves, curling or non curling you always get signs of deficiencies in the lower leaves. This I feel is more due to the age of the leaf than a sign of deficiencies as the head of the plant will always tell you the health of the tomato plant.
Leaves like this just really need removing, which you should be doing from the bottom up as you are getting closer to picking your first tomatoes.
TOMATO LEAF CURL ON DIFFERENT TOMATO PLANT VARIETIES 
I have also noticed that leaf curl varies on different varieties, for example the Red Pear Cherry tomatoes although having less mature fruit on them seem to be worse, so that blows the theory of strain on a plant causes leaf curling.


In conclusion, I have been involved in growing indoor tomatoes commercially and for pleasure for more years than I care to remember. Basic tomato leaf curl like in these photos has never ever been a problem, or affected the cropping. It could be a combination of some or all of the points mentioned, but please do not try to try and fix it by changing the basic rules of tomato growing, feed your plants at least once a week, water little but often so the roots do not drown, keep your greenhouse well ventilated in the summer and keep the frost off in early spring.  Tomatoes are one of the easiest crops to grow by sticking to the basic rules.