After the first week, the cabbage sprouts are one to two inches tall. This is the “Mei Ching Choi” variety of Brassica rapa.
Within a day after 90% had sprouted, I placed them under a fluorescent light and started an initial mist with a liquid fertilizer. The fertilizer is mixed from a seaweed concentrate, SeaCom-PGR, diluted approximately 1:1,000. This concentrate should be rich in cytokinin hormones and deliver a 0-4-4 mix (i.e., no nitrogen but phosphate and potassium), so it should help root growth.
I’m hoping these will be ready to transplant after 4-6 weeks. That will put them in the ground early, but I’m planning to plant in staggered groups about a week apart to leave some backups if there is a hard frost. And if we’re lucky, that will also get us some early cabbage!
If you’re trying this at home, too, and your seedlings aren’t looking too healthy, they may be afflicted by “damping off,” a complex of fungal disease that can affect germinating seeds and seedlings. More information about that at “How to Prevent Seedling Damping Off.”