Gardening Problems in Late Summer

Do you have a few garden problems cropping up at this time of year? As we move toward the end of the season, some gardeners may notice their plants don’t look quite as lush as they did in the spring and early summer. Growth may slow, lower leaves may brown and drop, and pests or fungal diseases might start to take hold. During hot afternoons, soft leaf tips might even droop or wilt.

Don’t worry—these are all common issues in late summer gardens. The good news? With a few strategic adjustments, you can help your plants finish the season strong. Read on to learn how to manage the most common late summer garden challenges.

Garden Problems #1: Insects

While many of spring’s nuisance pests—like slugs, cutworms, grubs, and flea beetles—have largely disappeared, other insect issues are just beginning.

This time of year, watch for:

• Japanese beetles, which skeletonize leaves and feast on flowers.
• Webworms, which spin unsightly nests in trees and shrubs.
• Spongy moths (formerly gypsy moths), whose caterpillars can defoliate trees.

Solutions:

• Hand-picking is a quick way to reduce visible beetles—drop them into a bucket of soapy water.
• Prune out webworm nests and dispose of them. Follow with an application of BTK (Bacillus thuringiensis kurstaki) to target caterpillars.
• Set out beetle traps in the early morning or late evening, away from plants you’re trying to protect. *Use with caution.*
• Monitor your lawn for signs of white grubs—look for wilting patches or animals digging. Apply beneficial nematodes in late summer to control grubs before they overwinter.

Click here to learn more about Japanese Beetles.

Garden Problems #2: Diseases

Heat stress and humidity create ideal conditions for fungal diseases like powdery mildew, black spot, and rust, especially on roses, squash, and other vulnerable plants. You may also notice discolouration, stunted growth, or leaf drop.

Solutions:

• Remove and discard (not compost!) any infected leaves.
• Prune crowded plants to improve air circulation.
• Apply a fungicide such as sulphur spray or Bordo Copper Spray at the first sign of trouble, and reapply every 7–10 days as needed.
• For disease-prone plants, consider pre-emptive treatment earlier in the season.

Vegetable Garden Watch:
If your tomatoes or peppers have developed dark, sunken spots on the bottoms, you’re likely seeing blossom end rot—a sign of calcium deficiency often caused by inconsistent watering.

To prevent this:

• Apply a calcium-rich amendment like lime, gypsum, or tomato fertilizer.
• Water consistently at the base of plants.
• Avoid letting soil dry out completely.

Click here to learn more about Bottom End Rot In Tomatoes.

Garden Problems #3: Water- Too much, Too Little, Too Late

Watering mistakes are a common issue in late summer. Overwatering can encourage rot and disease, while underwatering can stress plants and slow growth.

Tips for Watering Success:

• Use soaker hoses or drip irrigation to minimize water waste and keep foliage dry.
• Aim for 1–3 inches of water per week, depending on heat and rainfall.
• Water deeply and early in the day to reduce evaporation and discourage mildew.
• Mulch garden beds with 2–3 inches of organic material (like shredded bark or straw) to retain moisture and keep roots cool. Mid-to-late summer is a great time to top up your mulch.

Garden Problems #4: Fertilizing

As growth slows and plants work harder to produce blooms or fruit, fertilizer becomes even more important—but only in the right conditions.

What to fertilize:

• Annuals and late bloomers (like dahlias, zinnias, and cosmos) will benefit from a high-phosphorus fertilizer (like 15-30-15) applied every two weeks.
• Vegetables may also benefit from a mid-season boost, especially if you’re still harvesting.

What not to fertilize:

Lawns that are dry and dormant—fertilizer can burn the grass if there’s not enough moisture. Instead, wait until late summer or early fall, once the grass begins to green up again.

Bonus Tip: Weeds & Garden Clean-Up

As plants decline, weeds often seize the opportunity to spread. Keep up with weeding in late summer to reduce competition and prevent weed seeds from overwintering in your soil. Regular clean-up of dead foliage also helps reduce pest habitats and fungal spread.

Late summer isn’t the end of the garden season—it’s just a shift. With a little care and observation, you can manage the challenges of heat, pests, and disease while setting your garden up for a healthy, beautiful fall. Keep watering wisely, feed where needed, and enjoy every bloom the season still has to offer!