Check for weed trees invading your shrubbery

Weeding your garden is a great way to relieve stress after a workday. When you do, be sure to look inside any shrub plantings or hedges to see if there are any weedy trees. Boxelder, mulberry, Siberian elm and buckthorn trees will seed into the centers of shrubs and start growing. They can be hard to spot early on without looking closely. They’re easier to remove when they are small. I started looking under my hydrangeas and hostas in areas where an invasive weed called goutweed has been an issue before and found some growing hidden under the foliage.

Signs fertilizer is needed

If the plants growing in your containers or baskets are looking 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 liquid fertilizer as needed to perk them up. Annuals growing in garden beds may also benefit from fertilizer if they are stunted and off-color in growth, provided that other potential cultural problems like over or underwatering can be ruled out. Over fertilizing will result in large green plants with reduced flowering.

Pull or mow crabgrass

I have been seeing a good amount of crabgrass — which has a lighter green color and wider leaf blade than bluegrass — in lawns now, especially if they have been neglected. This annual weedy grass seeds readily in the fall. Keep it closely cut to prevent seed formation or pull it out by hand. There are herbicides that will control crabgrass at this time of year, but they will not be as effective after the crabgrass has set seed. Make note of bad areas in your lawn and apply a pre-emergent herbicide (one that prevents weed seeds from germinating) in early spring before lilacs flower.

Signs of cedar apple rust

Hawthorns with a more severe case of cedar apple rust may have foliage that turns bright yellow and drops prematurely. There will be small yellow spots that appear on leaves after infection in spring. This disease requires eastern red cedar (Juniperus virginiana) as an alternate host, so avoid planting this plant if you have hawthorns in your garden. Like crabapples, spraying now will not help your trees, as chemical controls need to be applied in spring to prevent this disease.

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