This is just as important as nutrition. During the first few weeks, the plants have a very limited root system. Keep the top 15cm of soil just moist but not soggy wet. Once the plants are well established, allow the top few centimetres of soil to dry out before resoaking the top 20cm. Tomato plants can withstand all kinds of stresses, including heat stress, providing they have a healthy root system and adequate – but not too much – moisture and nutrients.