Brassica rapa Grow in a greenhouse or protected area. Grow in shallow trays or 20-row flats. Broadcast seed thickly on the media surface with seeds 1/4"- 1/2" apart, and cover lightly with sowing mix, vermiculite, etc. Ideally, soil temperature should be 75Â°F (24Â°C) until germination, then reduced to 60Â°F (16Â°C). Maintain air temperature around 60Â°F (16Â°C). Bottom water or mist to prevent sowing mix from splashing on the seedlings. Maintain even moisture and do not allow sowing medium to dry out. If fertilizing, incorporate fertilizer into the sowing mix before sowing, or use a bottom watering system for liquid applications to avoid residue on the leaves.