The traditional method of growing cabbages has been to sow in a seed bed and transplant.

There they take the punishment from the weather, the pests and diseases.

If you are growing only a small number of plants, to start them off indoors can produce a few very strong plants that will resist the pests, even club root.

These Nero Kale are ready to go out.

kale

They are in big Origami Pots, fine root hairs are protruding through the sides. Strong tap roots from the bottom. When planted out they will be head and shoulders above any weeds that may germinate. Hopefully too tough for the Slugs and Snails. Also Cabbage Root Fly which often attacks young soft plants at transplanting time.
Water them in once and they can be almost forgotten about.