done with wire netting.
you can harvest spring cabbage at three different stage of their development. in early spring you can pull them before a head has formed, giving you young spring greens, if you do this every other plant then those plants left will have more space to mature to their full size.
the hearted plant should be ready in late spring and can be harvested by either lifting with a fork and then removing the heart, or if you are not clearing the ground for another crop you may want to cut the heart from the stem leaving the roots in the ground, these will then produce a second or 