How to Keep Cabbage Starts From Bolting
I have started several January King cabbage seedlings indoors under lights for growing over the winter. It's time to get them out into the garden, but I had a hard time this spring with my bok choy and kohlrabi bolting when they were still only four inches tall! How do I get my fall plants to grow without bolting this summer? I live at about 150 feet above sea level in West Linn within a half mile of the Willamette River, if this helps with climate. My backyard gets a lot of sun and is pretty darn warm on sunny days.
Clackamas County Oregon
Thanks for your question about your cabbage. Your last sentence says it all. Cabbage is a member of the brassica family, which, in (typically) mild climates such as ours, can be grown year round. They, like the 'cool weather' plants listed in this article can tolerate cooler weather, but wide swings in the temperature can also make them start to produce seeds (their only goal in life), or 'bolt.'
So, although it may seem counter-intuitive, planting them in early spring (after the last frost) or late summer (when the nights are getting cooler) will slow down the bolting process. Here's a little synopsis of it from the RHS; you can find cultivars of slow-bolting cabbage through several seed supply stores on the Internet. Here's another short article on the subject from UC Davis, with tips on some other cabbage issues.
Hope these are helpful. Good luck!