Plug transplants are available from specialized transplant producers when prearranged by contract. For production of on-farm greenhouse transplants, broadcast seed into a suitable soil mix or sterilized soil, transplant to other flats when seedlings are 1 to 2 inches tall. Move plants to the field when seedlings are 4 to 5 inches tall and temperatures are above 55 F. Larger transplants are more susceptible to bolting, to transplant shock, and are later maturing. Clipping the leaves of the seedlings results in greater uniformity, stronger stems, and allows more light to reach the slower-growing smaller seedlings. Such exposure preconditions celery to bolting and may result in severe losses in yield and quality.
Varieties differ in susceptibility to bolting.
Celery planted in the field around June 1 will be ready to harvest about October 1. Machine-transplant seedlings carefully to ensure a more uniform depth of planting and even growth. Never allow celery plant roots to dry out during handling and transplanting. Clip tops of transplants, if excessive, to reduce transplant shock. Planting before May 20 may result in excessive bolting unless plants are protected by row tunnels or field covers.