Will tomato plants produce well if I plant potatoes under the tomato plants?

Answer 1

No. Solanaceous plants should never be planted near other solanaceous plants. They are just close enough in relation to compete with each other for the same nutrients.

They can, however, be grafted together.

These articles will help you to graft plants: https://www.gardeningknowhow.com/garden-how-to/propagation/grafting/reattaching-broken-stems.htm

https://www.gardeningknowhow.com/garden-how-to/propagation/grafting/what-is-a-scion.htm

https://www.gardeningknowhow.com/garden-how-to/propagation/grafting/rootstock-information.htm