Zucchini in Zone 7B — Pacific Northwest

Zucchini thrives in our Pacific Northwest summers, making the most of our mild temperatures and cool nights that keep the plants productive without stress. Unlike gardeners in scorching climates who struggle with heat-stressed plants, you'll find zucchini happily producing tender, flavorful fruit through our entire growing season. The consistent moisture from our wet springs gives plants a strong start, and our long, gentle falls mean you can harvest well into October.

Our cool spring soils and shorter heat window do require some timing attention, but with our generous 193-day growing season, you have plenty of flexibility to get zucchini established and productive. The key is working with our climate patterns rather than fighting them.

Starting zucchini seeds indoors makes sense if you want to push your first harvest earlier or if our cool, wet spring weather has you feeling impatient. Start seeds in early to late April, about three weeks before you plan to transplant outdoors. Use seed trays with a seed starting mix and bottom watering to prevent fungal issues that can plague seedlings in our overcast spring days.

Keep seedlings warm (70-75°F) and under grow lights since natural light can be limited during our gray spring months. Don't start too early—zucchini grows incredibly fast and becomes rootbound quickly in small containers.

Honestly, most PNW gardeners skip indoor starting since zucchini establishes so quickly from direct seeding once the soil warms up. But if you're eager for that first summer squash, indoor starting gives you a 2-3 week head start.

If you've started seeds indoors, transplant your zucchini seedlings from late April through early June, once soil temperatures consistently stay above 60°F. Our spring soil can be surprisingly slow to warm even when air temperatures feel pleasant, so check with a soil thermometer before rushing.

Harden off seedlings gradually over a week, starting with just a few hours outdoors and building up their tolerance to our sometimes-brisk spring breezes and temperature swings. Space plants 36-48 inches apart—zucchini needs serious room to spread, and good air circulation helps prevent the powdery mildew that loves our mild, humid mornings.

Watch weather forecasts carefully during transplant season. Our springs can surprise you with unexpected cool snaps that will stress tender transplants, so have row covers ready as backup protection.

Direct sowing is the easiest and most reliable method for growing zucchini in the Pacific Northwest. You can sow seeds from late April through late August, giving you multiple opportunities for succession planting. Wait until soil temperatures reach at least 65°F—our cool spring soils need time to warm up properly.

Prepare planting areas by working in plenty of compost since zucchini are heavy feeders. Sow seeds ½ to 1 inch deep, spacing them 36-48 inches apart. This might seem excessive, but mature zucchini plants can easily spread 4-6 feet across. Plant 2-3 seeds per spot and thin to the strongest seedling once they're established.

For late summer plantings (July-August), direct sowing works especially well since the soil stays consistently warm and you avoid transplant shock. These later plantings often outperform earlier ones, producing right up until our first frost in late October.

Zucchini needs consistent, deep watering throughout our dry summer months—about 1-2 inches per week depending on plant size and temperature. Our typically mild summers (rarely above 90°F) mean you won't face the extreme water stress that gardeners in hotter regions deal with, but don't let that fool you into underwatering.

Use the finger test: stick your finger 2 inches into the soil near the base of the plant. If it's dry at that depth, it's time to water deeply. Always water at the base of the plant rather than overhead—those large zucchini leaves hold moisture and can develop powdery mildew in our cool nights, even during our dry summers.

During our peak growing season (July-August), established plants may need watering every 2-3 days. Morning watering works best, giving plants time to dry before our cooler evenings. Young plants need more frequent, lighter watering until their roots establish deeply.

A 2-3 inch layer of straw or grass clipping mulch helps tremendously with moisture retention and reduces watering frequency. This is especially valuable in the Pacific Northwest where our dry summers can catch new gardeners off guard after our wet springs.

Your first zucchini harvest typically starts in mid-June through late June if you planted in late April or early May, with continuous production through late October when our first frost usually arrives. With 50 days to maturity, even late plantings can produce a substantial harvest before winter sets in.

Harvest zucchini when they're 6-8 inches long and about 2 inches in diameter for the best texture and flavor. The skin should be glossy and easily pierced with a fingernail. Check plants daily during peak season—zucchini can seemingly double in size overnight during warm spells.

Cut the stem with a sharp knife rather than pulling, which can damage the plant. Look under large leaves carefully since zucchini hide well and can grow enormous in just a day or two. Those baseball bat-sized specimens are only good for zucchini bread.

Keep harvesting regularly to maintain production. As our long fall season progresses and temperatures start dropping in early October, plants slow down but often keep producing right up until frost. Those last harvests often have exceptionally good flavor thanks to our cool autumn nights.

Squash Vine Borers You'll notice sudden wilting of entire vines or sections, often with sawdust-like debris (frass) at the base of stems. If you slit open the stem, you'll find a fat, white grub tunneling through it. The clearwing moth that causes this lays eggs at the base of stems in early summer, and the larvae tunnel through stems, cutting off water flow.

In the Pacific Northwest, our cooler springs actually help since the moth flight period is later and shorter than in warmer regions. Wrap the base of stems with aluminum foil or use row covers early in the season. If caught early, you can inject Bt (bacterial insecticide) directly into stems. Plant succession crops every 2-3 weeks so you have backup plants if borers strike.

Powdery Mildew White or grayish powdery coating appears on leaves, stems, and sometimes fruit. Leaves eventually curl, yellow, and die back, reducing plant vigor significantly. This fungal disease thrives in our climate's warm days and cool nights, and surprisingly prefers dry leaf surfaces over wet ones.

Improve air circulation by spacing plants properly and removing lower leaves that touch the ground. Our morning humidity combined with cool nights creates perfect conditions for powdery mildew, so focus on keeping leaves dry. Neem oil or potassium bicarbonate sprays help, and surprisingly, a milk spray (1 part milk to 9 parts water) is quite effective.

Blossom End Rot Dark brown or black leathery patches appear on the bottom (blossom end) of fruits, often affecting the first fruits of the season. This isn't a disease but a calcium deficiency caused by inconsistent watering—exactly what can happen when our wet springs suddenly transition to dry summers.

The fix is simple: water consistently and deeply. Our dramatic seasonal moisture changes make this crucial in the Pacific Northwest. Mulch heavily to maintain even soil moisture as we transition from spring rains to summer dry spells. Don't over-fertilize with nitrogen, which interferes with calcium uptake.

Pacific Northwest Specific Challenges: Our mild summers and dry-summer climate actually reduce many pest pressures compared to hotter, more humid regions. However, the transition from wet springs to dry summers can create watering inconsistencies that lead to blossom end rot. Our cool nights and morning humidity can promote powdery mildew, but the same cool temperatures that cause this also slow down many other pests and diseases.

Plant zucchini with corn and beans in the traditional "three sisters" combination—the corn provides structure for beans while zucchini's large leaves shade the soil and suppress weeds. Radishes planted around the base of zucchini help break up soil compaction and may deter squash bugs. Mint planted nearby can help repel ants and aphids, though keep it contained since it spreads aggressively in our moist spring conditions.

Avoid planting zucchini near potatoes, which compete for similar nutrients and can harbor similar pests. In our Pacific Northwest climate, focus on companions that help with moisture retention and pest deterrence rather than heat protection, since our mild summers rarely stress zucchini plants from excessive heat.