August Gardening Tips and To-Dos for the Pacific Northwest

By August, the garden is in full swing. Dahlias are finally hitting their stride. Zinnias are throwing color in every direction. The sweet peas have faded, but there’s a whole second act coming.

This is also the time when the Pacific Northwest starts giving subtle hints that summer won’t last forever. The air feels a little different in both the mornings and evenings. The garden still has a lot to offer, but it’s worth paying attention to what’s coming.

These tips are written for Zone 8b gardeners, so adjust your timing depending on where you are. Here’s what I’m doing out there this month.

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August Gardening in the Pacific Northwest

August is when the garden peaks. Dahlias, zinnias, black-eyed Susans, and hydrangeas are all going at once. The bees are working overtime. The evenings are warm enough to sit outside and actually enjoy it all.

But August is one of the hottest and driest months of the PNW. Watering gets more critical. Some early summer annuals start to fade. A few things need attention before fall sneaks up on you.

I do a lot of my garden walkabouts in the early morning or just before sunset. It’s the best time to catch problems before they get worse, and it doesn’t hurt that the light is beautiful. August rewards the gardeners who stay tuned in.

15 August Gardening Tips for the Pacific Northwest

1. Water Deeply and At the Right Time

Water deeply so moisture reaches the roots, not just the surface. Early morning is best. It gives foliage time to dry before evening, cutting down on powdery mildew and other fungal issues.

Containers, hanging baskets, and window boxes may need watering twice a day in the heat spell. Check them every morning. They dry out faster than you think.

2. Give Heat-Stressed Plants Some Shade

Wilting leaves and scorched foliage are your cue. Temporary shade cloth can make a real difference during a heat event. I’ve draped shade cloth over my dahlia beds during our worst summer stretches, and it genuinely helps.

3. Top Off Your Mulch

Mulch does three things at once right now: keeps the soil cooler, slows evaporation, and knocks back weeds. If your beds look sparse, a fresh layer is one of the easiest things you can do this month.

4. Divide Overgrown Perennials

Late summer is a good time to divide daylilies and other perennials that have outgrown their space. You’ll get better blooms next year and free plants for other spots in the garden.

Daylilies are happiest when divided every four to five years. After they go dormant, cut them back. If you prune them to the ground now, they’ll often rebound once temperatures drop and may even produce a second flush of blooms in fall.

5. Keep Deadheading

Deadheading, removing spent blooms, redirects the plant’s energy back into producing new flowers. For dahlias, trim back any foliage showing powdery mildew at the same time. It keeps things looking better and helps slow down the spread.

6. Stake and Support Tall Flowers

By August, dahlias, snapdragons, and sedum ‘Autumn Joy’ are top-heavy and one good windstorm away from disaster. Check your stakes and supports now, before you have to deal with broken stems.

7. Stay Ahead of Weeds

Weeds compete with your plants for water, which they really don’t need to be doing in August. Pull them when the soil is damp after watering or rain. If time is short, at least snip the seed heads so they don’t spread.

8. Prune Out Disease and Dieback

If you see branches or stems showing disease or dieback, remove them now. Wipe your pruners with disinfectant between cuts, so you’re not moving problems around the garden. It’s a quick habit that saves a lot of headaches later.

9. Check Your First Frost Date

It’s not sweater weather yet, but start watching your average first frost dates. That information shapes your timing for fall planting, late-season harvests, and when to start your fall garden transition. In Zone 8b, we usually have more time than we think, but it’s better to be ready.

10. Harvest Often

Mornings are the best time to pick. Everything is cool, crisp, and at peak flavor. For flowers, an early harvest means longer vase life.

Regular harvesting also keeps plants productive. Letting things go to seed signals the plant to slow down. For cut flowers especially, the more you cut, the more you get.

Leafy greens need to come in before they bolt and turn bitter. Onions are ready to stop watering once the tops fall over and turn yellow. At that point, they’re curing, and you don’t want to interfere.

11. Watch for Slugs

Slugs don’t disappear in August. They just hide better. Look under leaves, containers, and debris, especially in shaded or damp corners.

I use Sluggo because it’s safe for pets and wildlife. Beer traps work too if you’re more of a DIYer.

12. Tackle Aphids and Mites

Aphids and spider mites can explode in August heat. Check under leaves and along stems. A strong spray of water knocks them back, or use an insecticidal soap spray for more persistent problems. Catch them early. Pest pressure compounds fast this time of year.

13. Deal with Powdery Mildew

Powdery mildew loves warm days and cool nights, exactly what August delivers. Remove affected leaves as soon as you spot them. Avoid overhead watering in the evenings. Better airflow between plants helps too. If it gets out of hand, a fungicide is your next step.

14. Save Seeds from Your Best Plants

Open-pollinated and heirloom varieties are worth saving. I’ve had favorites disappear from catalogs with no warning, and having your own seed stash is good insurance. August is a natural time to start collecting as things ripen.

Seed swapping with other gardeners is a fun way to get the seeds you want.

15. Refresh Bird Baths and Welcome Wildlife

Keep birdbaths and water features clean and topped off. Standing water becomes a mosquito problem fast. Refresh it every few days. Fresh water draws birds and beneficial insects to the garden, and honestly, watching them visit is one of the better parts of August.

Can I Still Plant in August in the Pacific Northwest?

Yes. You have more planting options than you might think.

Cool-Season Vegetables

Sow lettuce, kale, spinach, radishes, and carrots directly into the soil now. These crops actually prefer the cooler weather that’s coming, and they’ll produce well through early fall with consistent watering. This is one of the best windows for a fall vegetable harvest in Zone 8b.

Summer Plant Sales

Garden centers start marking down perennials and shrubs in late summer. If you’ve had empty spots all season, now’s a good time to fill them affordably. Plant healthy-looking specimens, water them in well, and they’ll have a few weeks to get settled before temperatures drop.

Order Spring Bulbs Now

I know it feels early. But if you want a strong showing of tulips, daffodils, and hyacinths next spring, August is the time to order. The best varieties sell out. Ordering spring bulbs now means you’ll actually get what you want when planting time comes in the fall.

August Gardening FAQ for Pacific Northwest Gardeners

What Should I Be Planting in August in Zone 8b?

Focus on cool-season crops: lettuce, spinach, kale, radishes, and carrots can all be direct-sown in August for a fall harvest. It’s also a good time to plant perennials and fall-blooming annuals while the soil is still warm enough to support root establishment.

How Often Should I Water My Garden in August in the PNW?

Most established garden beds need deep watering two to three times per week during dry spells. Containers and hanging baskets may need daily watering, sometimes twice a day during hot stretches. The key is watering deeply rather than frequently. You want moisture to reach the roots, not just to wet the surface.

When is the First Frost in the Pacific Northwest?

In Zone 8b west of the Cascades, first frost typically arrives in late October to mid-November, though it varies by location. Check your local average dates and use that information to plan fall planting timelines and when to start harvesting tender crops.

How Do I Deal with Powdery Mildew on Dahlias in August?

Remove affected leaves promptly and dispose of them away from the garden. Avoid watering overhead, especially in the evening. Improve airflow by pruning any overcrowded growth. For persistent cases, a sulfur-based fungicide or neem oil applied in the morning can help slow the spread.

Is It Too Late to Plant Sunflowers in August in the Pacific Northwest?

It’s probably too late for tall varieties of sunflowers that need a long growing season. They won’t have time to mature before fall. That said, a quick-maturing sunflower variety sown in early August might surprise you. Check the days-to-bloom on the seed packet and count backwards from your expected first frost.

August in the Garden

August is a lot of things at once. It’s peak color, peak harvest, and the beginning of the end of summer. There’s still so much happening out there, and it’s worth slowing down long enough to actually enjoy it.

Water consistently, keep an eye on pests, deadhead what needs it, and start thinking ahead to fall. The garden rewards attention this month more than almost any other.

Until next time,

Happy Gardening

I’m a self-taught hobby gardener. Everything I share on my blog is my opinion and what has worked for me.