How to Grow Celery

Why celery is a demanding crop

Celery is a biennial in the carrot family, grown for its leaf stalks. It is slow, it has a small, shallow root system that forages poorly, and it reacts badly to almost every kind of stress. Drought makes it stringy. Heat makes it bitter. A cold snap can make it bolt. UF/IFAS calls it a difficult crop in the home garden, and that is a fair warning.

Its comfort zone is narrow. Utah State Extension puts the ideal at 55-65°F, UC ANR at 60-65°F, and University of Maryland Extension says yield and quality are best between 55 and 75°F with good soil moisture and fairly high humidity. Plan the whole crop around keeping it in that window for three to four months.

Starting seed indoors

Sow seed 10 to 12 weeks before you plan to set plants out (see the dates for your zone above). The seed is tiny and carries natural germination inhibitors. Utah State suggests soaking it in water and replacing the water daily, which leaches out the inhibitors and gives a more even stand.

Press the seed onto the surface of the mix or cover it with only a dusting, then keep it constantly moist. UF/IFAS lists the seed depth as “on surface” and stresses high moisture at the seeding and seedling stage. Do not try to sprout it in hot conditions: UC ANR notes that heat pushes celery seed into dormancy.

Maryland’s transplant guidance is specific and useful at home:

• Hold the mix at 70-75°F until seedlings emerge, then grow them at 65-70°F.
• Keep night temperatures above 55°F so the plants don’t become “seeders” later.
• If seedlings get tall and spindly before planting out, clip them back to 5 or 6 inches.
• Harden them off by holding back water for 7 to 10 days. Never harden celery with cold, because chilling is what triggers bolting.

Utah State recommends that transplants have three or four mature leaves and a well-developed root system when they go into the garden.

Planting out and the frost question

Set plants out once the risk of frost and of a prolonged cool spell has passed. Sources differ on how much cold celery can take. Maryland says it survives light freezes but is damaged by moderate ones; Utah State calls it very susceptible to both spring and fall frosts. The practical answer is the same either way: in cold-spring regions such as the northern Plains, the Upper Midwest and the Mountain West, cover young plants with hot caps, plastic tunnels or fabric row covers. Utah State notes that covers also speed early growth, and black plastic mulch warms the soil enough to allow earlier planting.

The bigger danger is not a single frost but several days below about 55°F, which Maryland identifies as the trigger for seed stalks. That is why Maryland advises waiting until both frost and cold spells are past, not just the frost-free date.

Soil, spacing and blanching

Celery does best in fertile, well-drained soil rich in organic matter. Have the soil tested and work any fertilizer into the top 6 inches before planting. Utah State suggests a complete fertilizer high in potassium, such as 4-4-8, but Maryland links high potassium (along with excess nitrogen and sodium) to blackheart and to brown check, a cracking of the inner stalks. Let the soil test decide rather than adding potassium by habit.

Spacing advice ranges widely. Utah State sets plants 12 inches apart in rows 2 feet apart; UF/IFAS gives 6 to 12 inches with 18-inch rows; Maryland’s commercial figure is 8 inches. Closer spacing is a deliberate choice: crowded plants stretch upward with longer stalks, and Maryland notes that dense planting also helps blanch them. Maryland adds that blanching can improve stalk color and eating quality. Self-blanching varieties need no extra help, while other types can be blanched by trenching or similar methods.

Water and feeding

Steady watering is essential for good stalks. Give at least 1 to 2 inches a week from rain or irrigation and soak the soil thoroughly each time, because the roots sit close to the surface. Above 85°F, Utah State advises watering more often to limit stress and fiber. Drip irrigation is efficient and, according to Maryland, the evenness it provides also lowers the risk of blackheart.

Celery is a heavy feeder. Utah State recommends sidedressing with nitrogen, about ¼ cup of 21-0-0 per 10 feet of row, at 4 and 8 weeks after transplanting. Cultivate only shallowly to avoid cutting roots, and use an organic mulch to hold moisture and keep weeds down, since slow-growing celery competes poorly.

Growing celery in warm-winter regions

Where summers are hot, celery is a cool-season crop planted in late summer, fall or winter. UF/IFAS lists it for all three Florida regions: North Florida plants in late winter, while Central and South Florida plant from fall through winter. It recommends Utah strains and early-maturing varieties. In Arizona’s low desert the Maricopa County calendar starts seed from mid-August. UC ANR’s Riverside County Master Gardeners warn that desert-grown celery is often stringy and bitter, so steady water matters even more there. Inland valleys of Southern California plant in summer. Use the dates for your zone above.

Common problems

• Blackheart: the center leaves turn brown, then black, from a localized calcium deficiency. Maryland ties it to swings in moisture and nutrients, such as a burst of fast growth after heavy rain or irrigation followed by drought. Keep watering even; Maryland notes that soluble calcium drenches can reduce it.
• Bolting: caused by cold. Don’t plant too early and never chill seedlings.
• Stringy, bitter stalks: caused by drought and heat. Water regularly, especially before harvest.
• Aphids: they suck sap and can spread viruses. Knock them off with a strong water spray or use insecticidal soap.
• Leafminers: small larvae make pale, winding tunnels in leaves. Damage is usually minor, and natural enemies generally keep them in check.
• Powdery mildew: white patches spread from older leaves. Utah State recommends resistant varieties and watering early so leaves dry during the day.

Harvest

Snap off outer stalks once they reach a foot or more, or take the whole plant when it is at least 3 inches across at the base. UC ANR cuts whole plants just below the soil line through the taproot. Harvest before the stalks turn pithy, and avoid picking in hot, dry spells, when stalks are toughest. Home-grown celery keeps for up to about two weeks in the refrigerator. Utah State suggests 5 to 10 plants per person for fresh use and storage.