Conventional garden wisdom advises that to plant kale well spaced out, around 45cms, but that tended to be when the very large varieties of Kale were popular. Modern garden plots do not really accommodate the large varieties of Kale. Should you decide to grow, say Redbor, which grows up to 90cms, you will need a lot of space, but there are many smaller varieties which are more practical to grow.
Illustrated top left from my own vegetable plot is "Dwarf Green Curled, " which is a smaller variety which I plant closer around 25cms. You can pick some tender leaves early in the season and keep picking. Kale will carry on cropping well into the winter. By picking the leaves regularly, you can harvest the softer leaves. To my taste, this variety of Kale is less bitter than some other varieties. I have also grown "Westland winter" described as a semi tall variety, introduced to me by listening to Chef Raymond Blanc, who recommends it and it is a delicious variety to grow.
The dwarf varieties of Kale are ideal to grow where space is in short supply, or you want to grow in containers, or you just do not want Kale to take over.
Kale will tolerate all soil types, although it may not do well on acidic soil. If your soil has a low PH, it may be better to grow Kale in containers using a peat free compost. Grow kale in fertile soil with the plants well firmed in. The taller varieties may need staking in exposed areas . Kale grows in full sun and tolerates partial shade and needs no attention once the seedlings are established.
Kale is pretty well pest free.
Kale can be harvested all winter and may even produce a late spurt of leaves in early spring.