I use a rating system to help me decide what to grow and it considers lots of factors, but the main ones are how tasty it is, healthy it is to eat, how expensive it is to buy, how big it's harvest is, when it's harvest period is and whether I can buy it organically and if not how much it's sprayed.
Perennial kale scores exceptionally well in this system. The leaves taste good, a little more cabbagy than most kales, the plants are extremely prolific and provide their best harvest in late winter and spring when annual kales are at their least prolific.
Perennial kales seem to grow in most soil types, they will also tolerate light shade and surprisingly grow fairly well in large containers, of 50 litres or larger.
Plants are started from cuttings, which can be easily sourced on eBay. Cuttings are potted in a large (1 litre) pot and left to root for a few months. Then planted into their final location where they will grow strongly for a few years.
<aside> 💡 I do supply free cuttings to members of my buymeacoffee club, when I have them
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I find that plants are best replaced after 3 years though as they grow very tall and loose a lot of lower branches in storms.
Perennial kales rarely seed, but if the conditions are ‘right’ they do produce viable seeds, which I’ve successfully germinated and grown on.
Perennial kales are usually grown from cuttings, which I find are best taken in spring and autumn, but any time works. These plants are then large and well established the following year.
Perennial kales can be harvested at any time, but I prefer to leave mine alone during summer, and early autumn when annual kale is readily available. This means I have strong plants ready for harvest in winter and spring, when I need them most.
https://airtable.com/shrP0xL88HrlcPytS
It’s also possible to grow perennial kales as an annual, take cuttings in early autumn and over winter them in an unheated polytunnel or greenhouse (they might be ok outside in mild winters). Plant then out under fleece in March and leave the fleece on for about 2-3 weeks. They will be ready for harvesting in May and early June, a bit like a spring cabbage. You could have course continue to harvest these plants all through summer if you wanted to.