Celery (Apium graveolens) requires a long, uninterrupted growing season to produce crisp, flavorful stalks. Transplanting involves moving seedlings, typically started indoors 10 to 12 weeks prior, to the garden bed. This timing is sensitive because celery needs specific temperature ranges to thrive. Successful transplanting requires coordinating the plant’s developmental stage with external environmental conditions. Getting the timing correct prevents the plant from bolting, which results in bitter, inedible stalks.
Determining the Ideal Transplant Time
The decision of when to move celery seedlings outdoors depends on both the size of the plant and the readiness of the garden environment. Seedlings are developmentally prepared for transplanting once they display four to six true leaves and have reached a height of four to six inches. Moving the plants before they reach this stage can subject them to shock and slow their establishment.
Celery is a cool-season crop, but it should not be planted until the risk of a hard freeze has completely passed. Growers typically aim to set out the transplants two to three weeks before their local average last spring frost date. This timing allows the plants to establish themselves in the cool, moist soil before the summer heat arrives.
Soil temperature is a more accurate indicator than air temperature, and the soil should consistently register at least 50°F (10°C) before planting. The optimal temperature range for celery growth is between 60°F and 70°F (15°C and 21°C). Sustained exposure to temperatures below 50°F or above 75°F can cause the plant to initiate flowering, known as bolting.
Pre-Transplant Preparation
Before the move, a process called “hardening off” is necessary to acclimate indoor seedlings to the outdoor world. This gradual exposure toughens the plant tissue, reducing the shock that occurs when moving from a controlled environment to one with fluctuating temperatures, direct sun, and wind. The hardening off process should take place over seven to ten days immediately preceding the transplant date.
Start by placing the seedlings in a sheltered, shaded outdoor location for one to two hours on the first day, ensuring protection from strong winds. Each day following, the duration of outdoor exposure should be incrementally increased, and the amount of sunlight the plants receive should be gradually intensified. This slow acclimation allows the plant’s cuticle to thicken, which helps prevent sunburn and excessive water loss.
The garden bed requires specific preparation for this heavy-feeding, moisture-loving vegetable. Celery requires highly fertile, moisture-retentive soil that is also well-draining, often benefiting from a slightly acidic to neutral pH between 5.8 and 7.0. Before planting, amend the soil generously with aged compost or well-rotted manure. Adequate spacing is also important, with each plant needing six to ten inches of space for proper air circulation and root development.
The Celery Transplanting Procedure
The act of transplanting should be timed to minimize stress on the seedlings. Planting late in the afternoon or on an overcast day is recommended, as the lower light intensity and cooler temperatures reduce water loss through transpiration. Watering the seedling trays thoroughly a few hours before transplanting helps stabilize the soil structure around the roots, making removal easier.
When handling the seedlings, disturb the root ball as little as possible to prevent transplant shock. Gently push up from the bottom of the tray cell or tap the container side to release the entire root mass intact. Planting depth is important; celery must be set in the garden at the exact same level it was growing in the tray. Burying the crown, where the stems meet the roots, can lead to stem rot and plant failure.
After placing the seedling in the prepared hole, gently firm the soil around the root ball to eliminate air pockets. Immediately following the planting, a deep watering is necessary to settle the soil and ensure the roots have maximum contact with the surrounding medium. Maintaining consistent moisture is necessary for celery, particularly in the first few weeks after transplanting. Newly planted seedlings may benefit from temporary protection, such as a shade cloth, for the first few days if exposed to intense sunlight or heat.