Celery in Zone 7B — Northern California

Celery, with its crisp texture and refreshing flavor, is a rewarding addition to any Northern California garden. Its versatility in the kitchen, from soups and salads to snacks, makes it a worthwhile endeavor, especially with our long growing season.

While our region presents challenges like drought and the occasional heat spike, starting celery indoors and understanding its needs allows us to enjoy a successful harvest. With our 245-day growing season, you'll have plenty of time to nurture your celery from seedling to table.

Starting celery indoors is almost essential in our climate, giving it a head start before the weather warms up. Begin sowing seeds late December through mid January, roughly 10 weeks before you plan to transplant them outdoors.

Use seed trays and a good seed-starting mix. Celery seeds are tiny and need light to germinate, so don't bury them too deep – just gently press them into the surface. Keep the soil consistently moist; bottom watering helps avoid disturbing the delicate seeds. A heat mat can help speed germination, and once they sprout, provide plenty of light with a grow light to prevent leggy seedlings. Given our early springs, starting early is key.

Transplant your celery seedlings outdoors mid March through mid April, after they've developed a few true leaves. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Choose a spot with full sun to partial shade, and space the plants 8-10 inches apart. Our spring weather can be unpredictable, so keep an eye on the forecast and be prepared to cover the seedlings if a late frost threatens.

Celery is a thirsty plant, and consistent moisture is crucial for healthy growth, especially with our dry summers. Aim to keep the soil consistently moist, as even short periods of dryness can lead to bitter, hollow stalks. This is probably the most water-demanding vegetable you can grow here.

During the cooler spring months, check the soil moisture regularly using the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Once the summer heat kicks in, you'll likely need to water deeply several times a week, providing about 1-2 inches of water per week. Watering at the base of the plant is preferable to overhead watering, especially in our low-humidity environment, as it minimizes water loss through evaporation.

Pay attention to your plants: wilting leaves are a sign of underwatering, while yellowing leaves and soggy soil indicate overwatering. Adding a layer of mulch around your celery plants helps retain moisture and regulate soil temperature, which is especially helpful during our hot summers.

You can expect your first celery harvest early June through late July, about 85 days after transplanting. Look for outer stalks that are at least 8 inches long – you can harvest these individually as needed.

Alternatively, you can harvest the entire plant when the stalks reach 12 inches or more by cutting it off at the base. For a milder flavor, blanch the stalks by mounding soil around them a week or two before harvesting. To encourage continued production, harvest the outer stalks first, allowing the inner stalks to continue growing. As our first frost approaches around mid- November, harvest any remaining celery to prevent damage.

Celery can face a few challenges in our Northern California gardens, including bolting from temperature stress, hollow stalks, and stringy stalks from heat.

Bolting from temperature stress

• What it looks like: The plant prematurely sends up a flower stalk.
• What causes it: Fluctuations in temperature, especially a sudden cold snap or prolonged period of heat, can trigger bolting.
• How to fix/prevent it: Choose bolt-resistant varieties, provide consistent watering, and protect plants from extreme temperature swings with shade cloth or row covers.

Hollow stalks

• What it looks like: The celery stalks develop a hollow center.
• What causes it: Inconsistent watering or nutrient deficiencies, particularly calcium deficiency.
• How to fix/prevent it: Ensure consistent watering, especially during hot weather. Amend the soil with compost or a calcium-rich amendment like bone meal before planting.

Stringy stalks from heat

• What it looks like: The stalks become tough and stringy, with a less desirable flavor.
• What causes it: Prolonged exposure to high temperatures.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Consistent watering and mulching can also help keep the soil cool.

Northern California Specific Challenges: Our moderate-to-hot summers, combined with low humidity and dry-summer rainfall, demand careful attention to watering and shading. Be prepared to adjust your watering schedule based on the weather, and don't hesitate to provide extra shade during heat waves.

Companion planting can benefit your celery crop in several ways. Green beans are good companions because they fix nitrogen in the soil, which celery needs. Cabbage family members deter celery flies. Tomatoes provide shade, which can be helpful during hot spells. Onions repel some pests that might bother celery.

Avoid planting celery near carrots, as they compete for the same nutrients in the soil.