Plant crops in the soil

Plant crops in tilled soil in all the squares in that room. Water them every day (I
suggest planting crops that grow in the shortest time such as Turnips) and the door will
open when rune energy is displayed over all of them, keep them there as long as you like,
and you can use the runes it provides (new runes appear each day even if you use one and
you can still get through the door after you use them.)