Tomatoes have a special trick up their sleeve: the ability to grow new roots (adventitious roots) along any part of their stem.
Given enough moisture and light, these roots emerge from tiny bumps (also called root initials or tomato stem primordia, the earliest stage of root development) and can actually grow without soil.
If you live in an area with high humidity or you’re prone to overwatering your tomato plants, you may have seen the bumps turn white and become more prominent.
This tendency of tomato stem primordia to appear so easily can be used to your advantage.
By partially burying the tomato stem when you transplant a second time, you’re anchoring the plant more firmly in the soil and encouraging even more roots to form. Having a deeper, greater mass of roots helps your tomato plant be more resilient against wind, drought, pests, and diseases.