Use a soilless mix when filling large containers

The containers you are going to use for seasonal plantings should have at least one bottom hole for drainage. A layer of gravel in the bottom of the container is not 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.

Very large containers can be partially filled with wood chips, plastic bags filled with packing peanuts or empty plastic pots turned upside down to conserve soilless mix. Separate the wood chips from the growing mix with landscape fabric.

• It's a good idea to deadhead (manually pinch off spent flowers) of rhododendrons and azaleas after they finish flowering. This is also the correct time to prune their branches to reduce the size of the plant as needed.

It is best to prune lightly. You can increase the flower count for the following year by very carefully pinching off one-half of the sticky new green growth that emerges from the ends of branches near the spent flowers.

• 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. This will help the new plant get established in the ground more quickly.

Monitor watering needs carefully 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.

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