Q: What do you get when you plant kisses?
A: Two lips.

Explanation: You use your lips to kiss someone, that is, you use two lips: your upper lip (the one below your nose) and your lower lip (the one above your chin).  The expression “plant a kiss” means to kiss someone deliberately.  There is a flower called a tulip (sounds the same as two lip) which is typically planted in the fall and blooms in the spring.  This joke plays on the sounds of “two lips” and “tulips.”  Happy almost Valentine’s Day!