September began with the warmest weather of the year. Such weather is not uncommon for late summer here. It can happen as late as early autumn. Still, it can be disconcerting while weather should be cooling. Cool season vegetable plants that are technically now seasonable dislike such warmth. Cole vegetables are particularly responsive to weather.
Cole vegetables are within the Cruciferae family, which is alternatively the Brassicaceae family. They therefore also classify as crucifers or brassicas. They include various forms of broccoli, cauliflower, cabbage, collard, kale, kohlrabi, mustard, turnip, radish, arugula, rutabaga and Brussels sprouts. As variable as they are, several are of the same species.
Broccoli and cauliflower are floral vegetables, since their primary edible parts are bloom. Brussels sprouts, cabbage, collard, kale, arugula, mustard greens and turnip greens are foliar. Turnip, radish and rutabaga are roots. Kohlrabi is a distended stem. Mustard seed, which is a seasoning instead of a vegetable, is the only common fruiting cole vegetable.
Therefore, unlike most warm season vegetables, cole vegetables should not fruit or go to seed. Broccoli and cauliflower only begin to bloom, but do not finish prior to harvest. This is why most cole vegetables are cool season vegetables here. Warmth stimulates bolting and bloom, which ruins flavor and palatability. Cool weather prolongs vegetative growth.
Contrary to the implications of recent weather, cool season vegetables, including several cole vegetables, are seasonable. This is the time to sow seed for turnip, radish, rutabaga and other cool season root vegetables directly into the garden. Transplant of seedlings is disfiguring to roots. Weather should be cooler by the time new seedlings start to develop.
Arugula, turnip greens, mustard greens, collard, kale and kohlrabi likewise develop most efficiently from seed. However, transplanted seedlings can be adequately productive too. Because only a few broccoli, cauliflower, cabbage and Brussels sprouts plants are likely sufficient, cell pack seedlings are likely more practical than seed. Since they are already growing, they can get planted a bit later.