Yellow Squash in Zone 7B — Pacific Northwest

Yellow Squash is a rewarding addition to any Pacific Northwest garden. Its mild, slightly sweet flavor shines in summer dishes, and the prolific harvests mean you'll have plenty to share. Plus, those cool summer nights we enjoy actually concentrate the sugars, giving your squash even better flavor.

Growing Yellow Squash here in Zone 7B does present some challenges. We need to be mindful of our cool springs and the risk of late blight. But with a 193-day growing season, and a little planning, you can absolutely enjoy a bumper crop of this versatile vegetable.

Starting Yellow Squash indoors isn't essential in our climate, but it can give you a head start, especially if we're having a particularly cool spring. You can start seeds indoors from early to late April, giving them about three weeks before transplanting outdoors.

Use seed trays with a good quality seed-starting mix, and provide consistent warmth and light. Bottom watering is key – set your tray in a shallow dish of water and let the soil soak it up from the bottom. This encourages strong root growth and prevents damping off, which can be a problem with our overcast spring days.

Transplant your Yellow Squash seedlings outdoors from late April through early June, once the soil has warmed up a bit. Before transplanting, be sure to harden them off by gradually exposing them to outdoor conditions for about a week.

Space the plants 24-36 inches apart. Keep an eye on the weather forecast – a late cold snap can set them back. You might want to have some row covers handy just in case.

Direct sowing is the easiest and most common method for growing Yellow Squash in the Pacific Northwest. You can direct sow from late April through late August, but you'll get the best results from earlier plantings.

Prepare your soil well by amending it with compost. Yellow Squash needs warm soil to germinate, so wait until the soil temperature is consistently above 60°F. Plant seeds 1 inch deep and space them 24-36 inches apart. Yellow Squash grows quickly from seed.

Yellow Squash are thirsty plants, especially during our dry summer months. Consistent and deep watering is crucial for healthy growth and preventing problems like blossom end rot.

During our wet springs, you might not need to water much at all, but once the dry summer months arrive, you'll need to water regularly. A good rule of thumb is to give them at least 1 inch of water per week, possibly more during prolonged dry spells. Stick your finger about 2 inches deep into the soil – if it feels dry, it's time to water.

Water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases in our sometimes humid conditions. Water in the morning so the foliage has time to dry out during the day. Yellowing leaves can be a sign of both over and underwatering, so check soil moisture first. A layer of mulch around your plants will help retain moisture and suppress weeds.

You can expect your first Yellow Squash harvest from mid-June through late October, about 50 days after planting. The best time to harvest is when the squash are 6-8 inches long and the skin is still tender enough to dent with your fingernail.

Use a sharp knife or pruners to cut the squash from the vine, leaving a short stem attached. Harvesting regularly encourages the plant to produce more squash. As we approach our first frost in late October, harvest any remaining squash, even if they're a little smaller than usual. They won't ripen off the vine, but you can still use them in cooking.

Yellow Squash, like all garden vegetables, can have issues. Here are some common ones we see in the Pacific Northwest:

Squash Vine Borer

• What it looks like: Wilting vines that look healthy otherwise. You might see small holes in the stems near the base, with a sawdust-like substance nearby.
• What causes it: Squash vine borers are moth larvae that burrow into the stems and feed on the plant tissue.
• How to fix/prevent it: Wrap the base of the stems with aluminum foil to prevent the moths from laying eggs. If you see signs of borers, you can try to carefully slit the stem open and remove the larvae.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes fruit. Leaves curl, yellow, and die.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it.
• How to fix/prevent it: Improve air circulation through spacing and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays help. Milk spray (1 part milk to 9 parts water) is surprisingly effective.

Squash Bugs

• What it looks like: Gray-brown shield-shaped bugs on leaf undersides. Bronze egg clusters on leaves. Wilting leaves that turn brown and crispy.
• What causes it: Sap-sucking insects that inject toxin while feeding. Adults overwinter in garden debris and emerge in spring.
• How to fix/prevent it: Hand-pick adults and crush egg clusters. Board traps (adults hide under boards at night — flip and destroy in morning). Neem oil spray. Remove plant debris in fall.

Blossom End Rot

• What it looks like: Sunken, dark brown or black leathery patch on the bottom (blossom end) of fruit. Often affects first fruits of the season.
• What causes it: Calcium deficiency caused by inconsistent watering. It's a nutrient uptake problem triggered by drought/flood cycles.
• How to fix/prevent it: Water consistently. Mulch heavily to maintain even soil moisture. Don't over-fertilize with nitrogen.

Pacific Northwest Specific Challenges: Late blight can be a concern, especially during wet springs and early summers. Choose blight-resistant varieties if possible. Slugs can also be a problem, especially for young seedlings. Use slug bait or traps to protect your plants. Our cool springs and short bursts of real heat mean you need to get your timing right for the best harvest.

Companion planting can help your Yellow Squash thrive. Corn provides a natural trellis for vining squash varieties. Beans fix nitrogen in the soil, benefiting the squash. Radishes deter squash vine borers. Marigolds repel nematodes and other pests.

Avoid planting Yellow Squash near potatoes, as they compete for nutrients. Also, avoid planting them near brassicas (cabbage, broccoli, etc.), as they can attract the same pests.