Do you know any gardening tricks like... (continued inside)

I read that you can dig out a chunk of potato flesh and pack a tomato start in the hole, then plant the whole potato w/ tomato in the ground and grow tomatoes and potatoes in the same area.

I’ve also heard that you can graft various citrus plants onto each other and have 4 different citrus fruits off of “one tree”.

What are other neat space saving tricks like these for the garden?