Planters must have drainage holes in the bottom so the soil doesn't become too soggy and drown the roots of the plant. Large planters pose a problem because they may not have drip trays to catch the draining water, or they are too heavy to move to empty the trays. Letting them drain freely leads to wet spots on patios that are unattractive, may lead to mold growth or may cause staining from fertilizer salts in the water. Creating a drainage system for the large planters to capture the water prevents these issues.
Measure the width of the container and add 4 inches to the measurement to determine the size of drip tray needed. Measure round containers across the widest part to find the measurement.
Purchase a separate drip tray from a garden center that fits the required measurement. Alternatively, use a water heater tray for large pots or a large plastic serving tray for small pots. Wheeled plant carts with attached drip trays are also available from garden centers and make planters easier to move.
Set the planter on top the drip tray. If possible, do this before adding the soil and plants to the planter. Otherwise, have someone help you lift the heavy planter.
Water the plant as the soil surface begins to dry. Add water until it begins dripping out of the bottom drainage holes and into the drip tray.
Use a clean turkey baster to suck the water out of the drip tray. Squeeze the water into a watering can and use it on other plants or in the garden. Most of the excess water will drain from the planter within 30 minutes of watering.