earth up

To pile soil around the base of a plant in order to promote growth. A noun or pronoun can be used between "earth" and "up." You have to earth up your potatoes, as exposure of the tubers to sunlight can cause them to become toxic. A: "Hmm, so you've already earthed up the plants, and no improvement. Have you tried singing to them?" B: "Does that really help them grow?" These tomato plants over here look like they could use some help. Why don't you earth them up?