Container gardening success: Proper drainage and plant care techniques

The containers you’re going to use for seasonal plantings should have at least one bottom hole for drainage. A layer of gravel at the bottom of the container isn’t necessary. Fill the container with a lightweight, fast-draining soilless mix and avoid using heavy garden soil even if you amend it with compost. Leave enough space between the top of the growing medium and the lip of the pot to make watering easy. You can partially fill very large containers with plastic bags containing packing peanuts or empty plastic pots turned upside down to conserve soilless mix. I like to use empty plastic pots and growing medium bags to fill in my containers.

This is a great time of year to plant. The plants that have been grown in containers should be moist when planted in your garden. When you remove the plant and its root ball from the container, spread out or cut all the roots that have encircled the root ball. These roots have grown in a circle inside the container and could eventually girdle or choke the plant if not redirected to grow out and away from the plant. Correcting this will help the new plant get established in the ground more quickly. Carefully monitor for watering needs after planting as the lightweight container soil can dry out quickly and stress the plants. Generally, containerized plants need more frequent, but light watering to get them established with roots growing out into the garden soil.

If you are unable to quickly install the new containerized plants you purchased, it’s easier to keep them watered if you hold them in the shade before planting. Check the containers most days to make sure they are not drying out.

I like to deadhead rhododendrons and azaleas (manually pinch off spent flowers) after they finish flowering. This is also the right time to prune their branches to reduce the size of the plant as needed. It’s best to prune lightly. You can increase the flower count for the following year by very carefully pinching off half of the sticky new green growth that emerges from the ends of branches near the spent flowers.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.