Komatsuna is one of the cheapest all year round vegetables to buy in Japan when I was living in Niigata (新潟) apart from bean sprout (Malay-tauge, Japanese-moyashi). A poor student with a tight budget, every week I will grab a bundle of komatsuna from the shopping market rack to last me for a week. It usually cost about 100japanese yen a bunch (~RM3.20 at that time).
Komatsuna is more tolerant to cold than pak choi types, and can grow from cool-temperate regions that have temperatures down to- -10 degree celsius to subtropical climates.
I sowed komatsuna seed in middle of July. After more than 7days the seeds germinated. Picture taken on 19th July 2010.
I find that when the weather gets colder (in winter), the seedling grow very slowly compared grown in autumn. Growth development of komatsuna about 3 weeks later. They look ready to be transplanted in their final position. Dilemma ~space.
Komatsuna sowed in autumn and still growing nicely without any sign of bolting. Other asian leaf vegetables in our patch has already bolted producing many flowers like choi sum, pak choi, wong bok and chinese broccoli. Komatsuna has proved that it is the most hardy vegetable in cold temperatures compared with pak choi types.
Interestingly, I have less pests attack on komatsuna compared with its other brassica family. It seems caterpillars, snail or slug will dine on other brassicas leaves first, komatsuna will be the last resort to those pests.
The leaves, stalks and flowers are tasty, and are usually enjoyed in stir fries, but are also used in salads, added to soups, or pickled in salt. In eastern Japan, the leaves are added to ceremonial New Year rice cakes. The leaves are rich in minerals. Is only a relatively new sub-variety, and has been cultivated in Japan for only~100years.
Reference: Discovering vegetables herbs & spices by Susanna Lyle.