Parsnip - White Gem This popular variety has some resistance to canker and produces wedge-shaped roots with smooth, white skin and flesh. Sow outdoors thinly from February to May, where they are to crop, 1.5cm deep, directly into finely-prepared, light, fertile soil, which has already been watered. Allow 40cm between rows. Early sowings may benefit from cloche protection. Seedlings usually appear in 14-32 days. Thin plants to 20cm apart. Replace any dislodged soil. Water well until plants are established. Leave roots in the ground until required, as they improve after exposure to autumn frosts. Harvest from October to February.