Tips on container garden care, harvesting herbs and combating southern blight

During our nightly dog walks lately, I’ve been seeing some annuals that look like they’re struggling. If the plants growing in your containers or baskets are getting stunted or have leaves that are yellowing as summer goes on, they might need supplemental fertilizer. The frequent watering required for containers and baskets can leach nutrients out of the growing medium, so use a liquid fertilizer as needed to perk them up — ideally when the plants are moist, since fertilizing very dry plants can damage their roots. I’ve also seen annuals growing in beds that could benefit from fertilizer now.

If you want to plant short season plants like snap beans, broccoli, cabbages, cauliflower, carrots, mustard greens, spinach and radishes for fall harvesting, the first week of August is the time to do it. Continue to harvest herbs by either snipping foliage, drying entire sprigs or plants or freezing individual portions in ice cube trays, and pinch off developing flowers to keep essential oils and flavor in the plants’ foliage.

Even though it’s said to be rare in Illinois, we’ve found southern blight at the Chicago Botanic Garden. It’s a fungal disease that affects herbaceous plants (and some woody plants) and results in plant collapse and death. Southern blight likes very hot (from the upper 80s to the 90s Fahrenheit) and humid, wet weather. The pathogen can remain viable in soil for three to five years.

It affects many host plants and seems to favor hostas here; look for wilting plants with yellowing leaves that collapse and die. The key identifying characteristics are the presence of white, fuzzy mycelium — the vegetative part of a fungus, consisting of a network of fine white filaments — at the center of the plant’s crown near the soil line, along with sclerotia. Sclerotia are small, round “seedlike” growths that are white, reddish tan or brown. If you see the sclerotia at the base of your plants, then you most likely have southern blight affecting them.

Remove any infected plants right away, along with the soil around them. Plants in the vicinity and downslope from these plants could be infected but not yet showing symptoms, so you’ll want to monitor. Moving water can spread this disease, along with contaminated tools, plants, soil, gloves and shoes.

Where you’re dealing with southern blight, try to remove the soil to a depth of 8 inches and 6 inches away from the plant. Place the plants and soil in a heavy-duty trash bag and put it in the garbage. This debris should not be placed in your compost pile. Don’t do this work during wet conditions, and be careful to contain the soil and plant debris, since it can spread the disease. Also be sure to sanitize any garden equipment used to do this work. Then bring in fresh soil to fill any resulting low spots.

Some other good practices to help contain this disease: Avoid or at least minimize walking through the area that may have southern blight, don’t mulch since mulch helps create favorable conditions for the disease, avoid or minimize watering to avoid runoff, and don’t transplant anything from the infected area to other parts of your garden. There are also fungicides you can apply to help protect your plants.

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