Are you wondering what garden tasks should be at the top of your list in August and September? While many people think the gardening season is winding down, gardeners in Zones 3-5 still have plenty to do. Late summer is the perfect time to care for your plants, plant cool-season vegetables, prepare for spring blooms, and start planning for next year’s garden. This August and September Garden Checklist will help you stay on track so you can enjoy a productive garden now while setting yourself up for even greater success next season.
August and September are always a bit bittersweet in my garden. After spending months planting, watering, weeding, and watching everything grow, it’s hard to believe we’re already thinking about fall. Here in cold climate gardens (Zones 3-5), this time of year is busy. While some gardeners are winding down, I’m already thinking about extending the season, planting for fall, and making notes for next year’s garden.
The good news is that there is still plenty to do in the garden during late summer. A little attention now can make a big difference in how your garden finishes the season and how well it performs next year.
✔ Continue Monitoring for Pests and Disease
Don’t let your guard down just because summer is coming to an end. Late summer is often when pests seem to make one last push before cooler temperatures arrive. Continue checking the tops and bottoms of leaves for signs of insects, fungal diseases, or damage.
I make it a habit to spend a few minutes every morning walking through the garden with my coffee. It’s much easier to deal with problems when you catch them early.
✔ Water Wisely
August can be surprisingly dry in many cold climate gardens. Rather than watering a little every day, water deeply so the moisture reaches the plant’s root system. Deep watering encourages stronger, healthier plants that are better able to handle temperature fluctuations.
Container gardens are a different story. Pots and hanging baskets dry out much faster, especially during hot, windy weather. Be sure to check them daily, and don’t be surprised if they need watering once or even twice a day during heat waves.
Before watering, I always recommend sticking your finger a couple of inches into the soil. Your plants will appreciate being watered when they need it—not simply because it’s on your to-do list.
✔ Plant Cool-Season Crops
One of my favorite late summer gardening tasks is planting cool-season vegetables for a fall harvest. While everyone else is pulling plants out of the garden, we’re still planting!
Early August is a great time to sow:
🥬 Leaf Lettuce
🥬 Kale
🌱 Spinach
🌱 Swiss Chard
🌿 Mixed Greens
❤️ Radishes
If temperatures are still hot, consider starting seeds indoors or planting them in a partially shaded area of the garden. Young seedlings don’t appreciate intense summer heat, and giving them a little protection can greatly improve germination.
There’s something satisfying about harvesting fresh greens in September when most people assume the gardening season is over.
✔ Divide Spring-Blooming Perennials
Late summer is also the perfect time to divide many spring-blooming perennials. If you’ve noticed some plants aren’t blooming quite like they used to or have become overcrowded, now is the time to give them some attention.
Some good candidates include:
🌸 Iris
🌷 Peonies
🟣 Alliums
🌼 Other Spring Perennials
Dividing plants not only helps rejuvenate them but also gives you more plants to fill empty spaces in your garden—or to share with fellow gardeners.
✔ Order Your Spring Bulbs (of course my favorite 🌷)
If you’re dreaming of tulips, daffodils, and alliums next spring, don’t wait until fall to start shopping. August is one of the best times to order bulbs if you’re looking for specific varieties. Popular bulbs often sell out quickly, especially some of the more unusual or heirloom selections.
🌷 Tulips
🌼 Daffodils
🟣 Alliums
🌱 Other Spring Bulbs
Most bulb suppliers will ship them at the appropriate planting time for our colder growing zones, so ordering early helps ensure you get exactly what you want.
✔ Give Annuals a Mid-Season Haircut
By August, some annual flowers start looking a little tired and leggy. Don’t be afraid to give them a good trim. Pinching or cutting them back often encourages fresh growth and another flush of blooms before frost arrives.
A little deadheading and pruning can go a long way toward keeping containers and flower beds looking fresh well into September.
✔ Add Some Fall Color
If your garden puts on a spectacular show in early summer but looks a bit sleepy by late August, consider adding a few fall bloomers.
Some of my favorites include:
🌼 Mums
💜 Asters
🍁 Ornamental Kale
🌺 Sedum
🍂 Other Fall Bloomers
Adding a few pops of fall color can completely transform your garden and extend its beauty for several more weeks.
✔ Take Pictures and Make Notes
This is one of the most overlooked garden tasks—and one of the most valuable.
August and September are excellent months to evaluate your garden honestly. What plants thrived? Which ones struggled? Are there empty spaces that need filling? Did certain color combinations work well together?
Take lots of pictures. Trust me, by January you’ll have forgotten exactly where that beautiful peony was planted or which corner of the garden desperately needed more color.
I like to keep notes in my garden journal so I can plan smarter for next season.
🌿 My Final Thoughts
Late summer in a cold climate garden isn’t the beginning of the end—it’s simply the start of planning for what’s next. There are still vegetables to plant, flowers to enjoy, and plenty of opportunities to set your garden up for success next year.
Take a few extra minutes this August and September to walk through your garden, snap some photos, and enjoy all of the hard work you’ve put in this season. Gardening teaches us that every season has something worthwhile to offer, even as one begins to fade and another is waiting just around the corner.
Happy Gardening!
Debbie 🌿❄️🌸
Cold Climate Gardens
Helping Zone 3 & 4 Gardeners Grow with Confidence