How to properly fertilize and prune containers and beds for healthier plants

I have finally gotten around to working on my mixed shrub and perennial borders at home. A number of tree seedlings have moved in as well as other miscellaneous weeds. Simply weeding and reducing the size of a massive, more aggressive perennial made a huge improvement in the garden’s appearance with minimal effort.

Continue to groom your perennials and annuals by removing yellowing foliage and spent flowers. I took out some old ornamental onion flower stalks while leaving some cut off above ground. These stay masked by perennial foliage, but create a good habitat for pollinators.

Make note of perennials that have flopped and need staking so that you can install a support system next spring before the plants need it.

Gently prune back more vigorous perennials to keep your border from looking overgrown. If you cut leaves off at the base, this reduces the size of the plants without having them look pruned. You may want to leave certain dried flowers on plants such as astilbes and coneflowers for fall and winter interest. Goldfinches visit my coneflowers in fall and eat the seeds.

If the plants growing in your containers or baskets look stunted or have leaves that are yellowing, they may need supplemental fertilizer. The frequent watering required for containers and baskets can leach nutrients out of the growing medium. Use a liquid fertilizer as needed to perk them up. It is best to fertilize containers and baskets when the plants are moist. Adding a slow-release fertilizer to containers at planting will be helpful next year. I also add a slow-release fertilizer to annual beds installed for the summer season.

Fertilizing plants that are very dry can result in damage to the plants’ roots. Annuals growing in garden beds may also need some supplemental fertilizer, though overwatering can also cause annuals to be stunted or have yellowing foliage.

Be sure to identify the insects on any plants before treating them with an insecticide to determine whether the insect really is a problem. If it is, try to assess whether the damage being done warrants control. The presence of insects feeding on plants does not necessitate automatic treatment. Some insects are beneficial and help control other insects naturally.

If an identified pest is causing significant damage, it is important to use the correct control with proper timing. If a variety of treatments are available, use the least toxic control possible.

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