Broccoli in Zone 7B — Pacific Northwest

Broccoli thrives in our Pacific Northwest climate like few other crops can. Our cool, mild summers rarely stress this cool-season vegetable, while those refreshing nighttime temperatures help develop the tight, flavorful heads that make homegrown broccoli so superior to store-bought varieties. You'll taste the difference immediately – sweeter, more tender florets without the bitter edge that comes from heat stress.

While our wet springs can slow things down and keep soils cool longer than we'd like, broccoli actually benefits from this measured start to the season. With our generous 193-day growing season, you have plenty of time for both spring and fall crops, giving you fresh broccoli from late May clear through the first frost in late October.

Starting broccoli seeds indoors gives you the best control over timing in our unpredictable Pacific Northwest springs. Sow seeds from mid-February through early March, about 6 weeks before you plan to transplant outdoors. Use seed trays filled with quality seed-starting mix, keeping them at 65-70°F for optimal germination.

Place your trays under grow lights or in a sunny south-facing window, though our overcast spring days often make supplemental lighting helpful. Bottom watering works particularly well for broccoli seedlings – it keeps the soil evenly moist without encouraging the fungal issues that can develop in our humid indoor environments during late winter.

Your seedlings will be ready to transplant when they have 4-6 true leaves and sturdy stems. This indoor start method is especially valuable for spring crops, though you can also direct sow in summer for fall harvests when soil temperatures are more cooperative.

Plan to transplant your broccoli seedlings from early to late April, once the soil has warmed slightly and our last frost window has passed. Start hardening off your seedlings about a week before transplanting by gradually exposing them to outdoor conditions – begin with a few hours of filtered sunlight and work up to full outdoor exposure.

Space your transplants 18-24 inches apart to give them room for their substantial heads and root systems. Our cool, moist spring weather is generally ideal for transplanting, but watch for those late cold snaps that can still surprise us in April.

Plant on a calm, overcast day if possible, as our spring winds can stress newly transplanted seedlings. The combination of cool soil and variable spring weather means your transplants may sit still for a few weeks before taking off – this is completely normal for our region.

Broccoli needs consistent moisture throughout the growing season, but our dry-summer climate means you'll need to stay on top of watering once the spring rains taper off. During our wet spring months, you may rarely need to water at all, but come July and August, plan on providing about an inch of water per week.

Check soil moisture by sticking your finger 2 inches deep – if it's dry at that depth, it's time to water. Water deeply at the base of the plants rather than overhead, which works well with our low summer humidity and helps prevent foliar diseases. Inconsistent watering leads to bitter flavor and premature bolting, especially critical during those occasional warm spells when temperatures climb into the mid-80s.

Apply a 2-3 inch layer of organic mulch around your plants once summer arrives. This conserves moisture during our dry months while keeping the soil cool – particularly important since broccoli performs best when soil temperatures stay below 75°F. Watch for signs of water stress like wilting during the warmest part of the day or leaves developing a blue-green tint.

Your first broccoli heads will be ready from late May through mid-July, depending on when you transplanted and which variety you're growing. Look for tight, compact green heads with small, uniform florets – harvest immediately when you notice any yellow flowers starting to show, as the flavor becomes bitter once flowering begins.

Cut the main head with about 6 inches of stem using a sharp knife, making your cut at an angle to shed water. Don't pull up the plant – those stems will produce smaller side shoots for several more weeks of harvest. These secondary heads are often more tender than the main head and perfect for stir-fries or steaming.

Keep harvesting side shoots regularly to encourage continued production. In our mild fall climate, plants often keep producing right up until the first frost in late October. If temperatures suddenly spike during summer, harvest any remaining heads immediately, as heat causes rapid deterioration in quality.

Cabbage Worms You'll spot these smooth green caterpillars munching irregular holes through your broccoli leaves, often leaving dark green droppings behind. White butterflies fluttering around your plants are a dead giveaway that eggs have been laid. These pests can quickly defoliate young plants in our mild summer climate where multiple generations thrive.

The larvae of imported cabbage white butterflies cause this damage, and our long, mild growing season allows several generations to develop. Bt (Bacillus thuringiensis) spray provides excellent organic control – apply in early evening when beneficial insects are less active. Floating row covers prevent egg-laying entirely, while handpicking works well for small plantings.

Clubroot Infected plants show stunted growth and wilting during warm afternoons, even with adequate soil moisture. When you dig up affected plants, the roots appear swollen and club-shaped rather than fibrous. This soil-borne disease persists for over a decade once established and thrives in our naturally acidic Pacific Northwest soils.

The pathogen Plasmodiophora brassicae causes this devastating disease, particularly problematic in our wet spring conditions and acidic soils. Raise your soil pH to 7.0-7.2 with lime applications, improve drainage with raised beds or organic matter, and maintain a strict 7-year rotation for all brassica crops. Never compost infected plants.

Bolting in Heat When temperatures consistently reach the low-to-mid 80s, broccoli sends up flower stalks and the leaves become tough and bitter. The heads become loose and inedible as the plant redirects energy to seed production. Even our mild heat waves can trigger this response in heat-sensitive varieties.

Extended warm periods above broccoli's comfort zone cause this premature flowering. Time your main crop for harvest before our warmest summer weather arrives, typically early to mid-July. Choose bolt-resistant varieties for summer plantings, provide afternoon shade during heat spells, and maintain consistent soil moisture with mulch to keep root zones cool.

Pacific Northwest Specific Challenges: Our region's combination of wet springs and dry summers creates unique challenges – slugs love young transplants during moist spring weather, while inconsistent watering during the dry summer months stresses plants into bolting. The key is managing moisture extremes and protecting young plants during our slug-friendly spring conditions.

Plant broccoli alongside beets and celery, which appreciate similar cool conditions and consistent moisture without competing heavily for nutrients. Onions make excellent companions by deterring many brassica pests with their strong scent, while potatoes work well as they're harvested before broccoli reaches full size, maximizing your garden space during our relatively short growing season.

Avoid planting broccoli near tomatoes, peppers, or strawberries – these crops prefer different soil pH levels and watering schedules that don't align with broccoli's needs. In our Pacific Northwest climate where space is often at a premium and growing conditions can be variable, choosing compatible companions ensures all your plants thrive together rather than competing for resources.