Utah State University Extension
This fact sheet discusses what is needed to grow quality (compact, well rooted, healthy) transplants. It introduces things to consider when producing vegetable transplants. Transplants are commonly grown in greenhouses. Success depends on knowing the right conditions needed for the crop of interest so the plants are the correct size, are healthy, and capable of withstanding the transition from the greenhouse to the field. Briefly covered are: transplanting tray selection, transplant age and scheduling, growing mixes and soil media, seeds and seeding, what transplants need , diseases andother problems, and conditioning or hardening transplants.
Drost, Dan, "Vegetable Transplant Production" (2015). All Current Publications. Paper 704.