Planter boxes, which come in a variety of sizes and shapes, offer the home gardener the option of having a larger container garden than a simple pot or hanging basket provide. Typically made out of wood or plastic, planter boxes serve as a decorative accent on decks, porches and patios.
Flip over the planter and examine the bottom for drainage holes. The planter should have drainage holes spaced every 2 to 3 inches along the bottom of the planter. If it doesn't, consider drilling your own drainage holes. If the planter can't be drilled, place a smaller pot with a drainage tray inside the larger planter.
Choose a permanent location for larger planters since weight will increase considerably after filling the container with potting soil. Base your choice on the light requirements of the plants to be repotted in the planter box.
Place a thin layer of gravel or broken potshards along the bottom of the planter to keep soil from running out of the planter. This layer shouldn't be thick and can simply block the drainage holes slightly to prevent soil loss.
Fill the planter two-thirds full with potting soil. Avoid using garden soil since this type of dirt doesn't hold water as well and blended peat/vermiculite (absorbent mineral beads) potting mixes. Potting soil retains more moisture and allows water to flow more freely through the confined planter environment.
Decide on the design of your planter. Remove plants from their existing containers and sink your fingers into the root ball. Loosen the roots with your fingertips to encourage outward growth in the larger planter. Repotted plants should be moved into containers that will accommodate expansion and allow for mature plant size.
Position the plant inside the planter so the top portion of the root mass lies about 1 to 2 inches below the planter rim. Fill in around the plant with loose potting soil and firm with your hands. No roots should be exposed above the soil surface.
Water at the base of the each plant to moisten the potting soil. Wait 10 minutes and water the plant again. Potting soil in the planter should be uniformly damp throughout without being soggy.
Gauge soil moisture regularly since container-grown plants require more water than their garden-bound cousins. Check the soil by sifting it through your fingers. If the soil compacts and holds shape, you don't need to add water. Powdery or light colored potting soil requires water.