Celery requires long, temperate growing seasons and takes about 105 to 130 days to mature enough for harvest. It does not like extreme temperatures and grows best with conditions under 75 °F during the day and between 50 and 60° Fahrenheit at night.
Choose an area with full sun and/or partial shade. While preferring a temperate climate, celery also enjoys full sun if possible. However, it will grow well in partial shade (at least 6 hours of direct sunlight) as well.
Choose an area with rich, moist soil. Originally a wetland plant, celery can tolerate relatively moist soil conditions that other vegetables cannot. However, make sure the planting area you choose is not prone to flooding.
Celery varieties prefer slightly acidic soil with a pH between 6.0 and 7.0. Though celery does not require impeccable drainage like most vegetables, it does require rich, healthy soil. Evaluate the soil's calcium and magnesium levels in order to determine what type of limestone to add to your soil. If the soil is low in magnesium, add dolomitic limestone. If it is high in magnesium, add calcitic limestone. Add the limestone 2 to 3 months before planting if possible, to allow the soil to absorb it. After adding, check the pH again. Into your garden beds, mix about 4 inches of organic fertilizer, such as manure or compost, into your soil. Celery likes extremely rich, organic soil. This will help the seedlings grow into strong, producing plants. Mix in your favorite nitrogen-rich fertilizer just before planting as well.
Start your celery seeds indoors 10-12 weeks before the last spring frost. To speed up germination, you can pre-soak your seeds in water overnight. Cover with about ¼ inch of potting soil, but do not pat down with your fingers after sowing the seeds. Celery seeds need a lot of light to germinate. Water the peat pots to moisten the soil after planting your seeds.
Place your seeds in a warm place so that the soil stays between 70 and 75° F until the seeds germinate. This should take 2 to 3 weeks. After germination, place the seedlings in a cooler indoor location so that the soil is between 60 and 70° F. Carefully thin the seedlings so that there is only 1 per cell after they germinate.
Transfer seedlings to the garden 2 weeks before the last spring frost. Make sure that it is not too cold outside. Celery can handle a light frost, but temperatures below 55 °F in the day and 40 °F at night for longer than 1 week can harm your celery plants. Give the seedlings plenty of space. Plant the seedlings 6 to 12 inches apart in rows 18 to 36 inches apart.
Celery requires constant moisture, so do not allow the soil to dry out at any time. If celery does not get enough water, the stalks will be stringy and bitter. Be sure to water several times per week and increase your watering routine during particularly warm or dry spells.
Celery plants are heavy feeders that require rich soil that must be fertilized frequently. To keep your celery plants happy, fertilize with a nitrogen-rich fertilizer every few weeks from planting to harvest.
You can begin to harvest the stalks when they reach 8 inches in height. Make sure to begin your harvest from the outside stalks and work inward. This allows the innermost stalks to continue to mature. Once mature, celery can sit in the ground for about 1 month as long as the soil remains a cool temperature between 60° and 75° F. The longer the celery grows and the darker it becomes, the richer in antioxidants and more nutritious it will be. However, it will also become more tough and fibrous.
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