Celery in Zone 7B — Pacific Northwest

Celery, with its crisp texture and refreshing flavor, is a rewarding challenge for the Pacific Northwest gardener. Freshly harvested celery offers a taste far superior to anything you'll find in the store, and its versatility in soups, salads, and snacks makes it a worthwhile addition to your garden. The cool nights here actually enhance the sweetness of celery.

Growing celery in the PNW does require a bit of planning, as our springs can be slow to warm and late blight can be a concern. However, with our long, mild fall and a 193-day growing season, you have plenty of time to coax these plants to maturity if you start early indoors.

Starting celery from seed indoors is essential in our region. Begin in late January through mid February, giving your plants about 10 weeks to develop before transplanting. Celery seeds are notoriously slow to germinate, so patience is key.

Use seed trays with a good seed-starting mix. Celery seeds need light to germinate, so gently press them into the surface of the soil instead of burying them. Place the trays in a warm location (around 70-75°F) and provide supplemental light. Bottom watering helps keep the soil consistently moist without disturbing the tiny seeds.

Remember that our spring weather can be unpredictable; overcast spring days are common, so make sure your seedlings get enough light to prevent them from becoming leggy.

Transplant your celery seedlings outdoors in mid April through mid May, once the danger of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

Space the plants 8-10 inches apart in a location that receives full sun to partial shade. Our mild summers mean celery generally appreciates some afternoon shade, especially during the hottest part of the day (which is rarely above 90°F).

Celery is a thirsty plant, and consistent watering is crucial in our dry-summer climate. It's probably the most water-demanding vegetable you can grow. Aim to keep the soil consistently moist, but not waterlogged. Even short periods of dryness can lead to hollow, bitter stalks.

During our wet springs, you may not need to water as frequently, but once the dry summer months arrive, you'll need to water deeply several times a week. Use the finger test: stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. Aim for about 1-2 inches of water per week, depending on rainfall. Water at the base of the plants to avoid wetting the foliage, which can encourage late blight.

Signs of underwatering include wilting leaves and stunted growth, while yellowing leaves and mushy stems can indicate overwatering. A layer of mulch around the plants helps retain moisture and suppress weeds.

You can expect your first celery harvest from early July through late August, about 85 days after transplanting. Look for outer stalks that are at least 8 inches long. You can harvest individual stalks as needed, allowing the plant to continue producing.

Alternatively, you can cut the entire plant at the base when the stalks are about 12 inches tall. Some gardeners blanch the stalks by mounding soil around them to exclude light; this results in milder-flavored stalks. To harvest without damaging the plant, use a sharp knife to cut the stalks cleanly at the base.

As our first frost approaches in late October, harvest any remaining celery, even if it's not fully mature. You can store it in the refrigerator for several weeks.

Here are some common problems you might encounter growing celery in the Pacific Northwest:

Bolting from Temperature Stress

• What it looks like: The plant prematurely sends up a flower stalk, making the stalks bitter and inedible.
• What causes it: Fluctuations in temperature, especially cold snaps after warm spells, can trigger bolting.
• How to fix/prevent it: Choose bolt-resistant varieties. Consistent watering and mulching can help regulate soil temperature. If a cold snap is predicted, cover the plants with a frost blanket.

Hollow Stalks

• What it looks like: The celery stalks develop a hollow center, reducing their crispness and flavor.
• What causes it: Inconsistent watering and nutrient deficiencies, particularly a lack of boron.
• How to fix/prevent it: Ensure consistent watering, especially during dry periods. Amend the soil with compost or a balanced fertilizer before planting. A soil test can help identify any nutrient deficiencies.

Stringy Stalks from Heat

• What it looks like: The celery stalks become tough and stringy, making them less palatable.
• What causes it: High temperatures and lack of moisture.
• How to fix/prevent it: Provide afternoon shade and ensure consistent watering. Choose varieties that are more heat-tolerant.

Pacific Northwest Specific Challenges: Our cool soil in spring can slow down growth, making it important to start celery indoors. Late blight, a fungal disease, can be a problem in our region's wet springs and summers. Ensure good air circulation and avoid overhead watering to prevent blight.

Companion planting can help improve celery's growth and deter pests.

Good companions include green beans, which fix nitrogen in the soil, benefiting celery's growth. Cabbage family plants help deter celery pests. Tomatoes provide shade during our mild summers, and onions repel some pests.

Avoid planting celery near carrots, as they compete for the same nutrients in the soil, potentially stunting the growth of both plants.