Gadenin日本語Get the appOrnamental kale is a biennial and spring is its second year
This plant runs on a two season clock. It spends the first season building a rosette of leaves and storing food in the stem and roots. The winter cold it needs to color is the same cold that satisfies its requirement for a chilling period, and once that requirement is met and the days lengthen in spring, it does what it was always going to do: it flowers. The rosette that took months to build is dismantled from the inside in a matter of weeks to fund a flower stem.
So the spring flower spike is not a failure of care, a symptom of stress, or something you did wrong. It is the end of a completed life cycle. Understanding this changes how you plan, because it means ornamental kale is a single season display that finishes in spring, not a plant you keep from year to year. Treat it the way you would treat a spring bulb display that is over rather than a shrub that has disappointed you.
How the spike develops, and what you see first
The first sign comes before any stem is visible. The center of the rosette, which has been a flat colored whorl all winter, starts to look domed and slightly ruffled, and the smallest central leaves change shape, becoming narrower and more upright than the leaves around them. Within a week or two a thick stem elongates out of that center, carrying those narrow leaves up with it and pulling the colored whorl apart.
The stem goes up fast, typically reaching two to three feet (60 to 90 cm), and it branches at the top into loose sprays of clustered green buds. Those open into small four petalled yellow flowers, the standard flower of the cabbage family, and they keep opening upward over several weeks. The color in what remains of the rosette drains away to green as the plant pulls resources up into the stem, and the lower leaves yellow and drop steadily.
| Stage | What it looks like | Roughly how long |
|---|---|---|
| Center domes up | Middle looks raised and ruffled, small leaves narrowing | 1 to 2 weeks |
| Stem extends | Thick upright stem lifting out of the rosette | 2 to 3 weeks |
| Buds cluster | Tight green buds in sprays at the top | 1 to 2 weeks |
| Yellow flowers open | Small four petalled yellow flowers, opening upward | 3 to 5 weeks |
| Seed pods form | Slim upright green pods along the stem | 4 to 6 weeks |
You cannot stop it, and cutting it out does not help
Cutting off the emerging spike is the obvious reaction and it does not work. The plant has already committed, and it will simply push side shoots from lower down that flower in turn, on a plant now missing its center and looking considerably worse than it did. The colored rosette is gone either way, because those colored leaves were the youngest leaves at the growing point and the growing point has become a flower stem.
Nor can you delay it by feeding, watering, cutting back or moving the plant. The trigger is the combination of accumulated cold and lengthening days, both of which are outside your control. The only real choice is between removing the plant when the display ends and letting the flowering run for the reasons below.
Record the date the center first domes up, in the same place as your sowing date and your first color date. Together those three dates describe the full useful life of the plant in your particular garden, and they tell you precisely how many weeks of display you actually get, which is the number worth knowing when you plan next year's sowing.
Reasons to leave it flowering
There are decent arguments for not pulling it immediately. The yellow flowers open at a point in early spring when very little else does, and they are heavily worked by early bees and hoverflies at exactly the moment those insects most need something. The hoverflies that breed nearby will spend the rest of spring eating aphids on your other plants, which is a practical return on leaving one or two plants standing.
The flowering shoots are also the best eating the plant ever offers. Picked in bud, before the yellow opens, the tender top few inches of the stem cook like sprouting broccoli and are noticeably sweeter and less coarse than the winter leaves ever were. Picking them repeatedly keeps the plant producing side shoots for several more weeks, which is the one intervention that genuinely extends its useful life, even though it does not bring back the color.
Seed, and why saving it is usually a waste
Left to finish, the flowers set slim upright pods that dry to pale brown and split. The seed is viable and easy to collect. The problem is that the cabbage family is promiscuously insect pollinated and will cross freely with any other member of the species flowering nearby, which in a garden means any kale, cabbage, broccoli, brussels sprout or collard that has also run to flower.
On top of that, the plants sold and grown for winter color are highly selected, and seed saved from them segregates badly. Sowing it typically gives you a mixed row in which some plants make a decent colored rosette, many make loose, mostly green leaves, and a few are simply plain kale. Pull the plants once the display is over and the flowering has served whatever purpose you wanted from it, clear the debris so it does not carry aphids or clubroot forward, and start again from fresh seed in mid summer.