The Planter can be filled with many different types of soils, allowing the related plants to grow on them without requiring any nearby water.

To fill with soil, place an empty planter and right-click it with the soil you want in it.
To create farmland planters, till a dirt planter with a hoe.
To fertilizer a planter click on a farmland planter with bonemeal.
To remove the soil, right-click with a shovel or a bucket for the water planter.