Whether you are filling containers and planters with ornamental flowers or vegetable crops, making the most of the limited space is a must. Extra large planters require more soil and the plants in them are overwhelmed by the size of the planter if they aren't planted near the rim. It is expensive to provide that much soil and a waste--most plants require no more than a 10 to 14 inch soil depth in order to flourish. Put the planters to use by solving this issue.
Drill drainage holes in the bottom of the planter if none are already present. Drill 1/2 inch holes 4 inches apart around the bottom edge.
Fill the planter one-third full with a filler material. Use crushed cans, empty plastic bottles or Styrofoam peanuts. Fill it loosely so water still drains between the filler.
Cut a piece of landscaping cloth to fit inside the planter. Poke 10 to 15 holes in the cloth to aid drainage through the material then set inside over the filler.
Fill the pot with a quality potting mix to within 2 inches of the pot rim. Mix a slow release, balanced fertilizer in with the soil.
Plant the transplants in the pot to the same depth they are at in their nursery containers. For ornamentals, plant taller plants in the centers of the pot and shorter plants around the edges to give a mounded appearance. Space vegetable plants 6 to 10 inches apart, or plant a single large plant such as a tomato in the center with low growing companion herbs such as basil around the rim.
Check the soil moisture daily and water as needed. Water when the surface of the soil begins to feel dry. Add water until it begins to run out of the bottom drainage holes.
Begin fertilizing two months after first planting in the planter. Use a half strength liquid fertilizer every two weeks until the end of the growing season.