The GARDENA gardening expert
Contact between the leaves of tomato plants isn't in itself a bad thing. It only becomes problematic if the plants become too densely leaved and therefore badly ventilated. In this case, leaf diseases such as leaf blight can spread across the leaves, which then remain damp too long. It is correct to protect your tomatoes from the rain in your small greenhouse, but inside the greenhouse, condensation will precipitate – generating the same risk.
This means that as long as you ventilate the excess water vapour by correct ventilation of your greenhouse, so that the leaves mainly remain dry, the risk of infection is less than without correct ventilation. However, the development of the plants should be observed carefully. In order to achieve better ventilation of the plants, you can also “play” with the size of the pinnate leaves. You do not have to remove them completely, but rather only parts of them, so that they no longer contact the neighbouring tomato plants.
Removing the lower leaves is not quite as important in a small greenhouse as outside, where rain sprays up bed earth containing fungi spores onto the lower leaves, and can thus infect them. Removing these leaves in a small greenhouse would rather serve the purpose of improved ventilation in the lower sections of your tomato plants.
If you wish to ensure increased air circulation in general, simply install a small fan, controlled by a timer, which at least in part is operated during the times of day when condensation is formed. In this way you can ensure that the greenhouse corners are also correctly ventilated.