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What is bolting


Swiss Chard with large leafy leaves Oriental salad in a container

Early bolting is a serious affliction in vegetables grown for their leaf production: Swiss Chard (left) and a tray of Oriental brassicas (right).


At Sea Spring Seeds, we are serious about bolting. And so we should be since bolting is an irreversible change that brings the productive lives of both root and leafy vegetables to a sudden and unceremonious end. Cold weather often triggers bolting, especially in young plants, and sowing when temperatures are warmer can sometimes solve the problem. Drought is also a stimulus, so be sure to keep your plants well-watered. Fortunately, varieties display huge differences in their resistance to bolting, and every year we design our trials to help us identify the most resistant.

What is bolting?

Often used but seldom understood, the term 'bolting' refers to a fundamental change in a plant's life cycle. Bolting progresses in series of fairly predictable steps, most of which can be clearly seen and identified in mustards and Oriental leafy brassicas.

If you look at an individual plant of both these leafy vegetables, you will see that the leaves are arranged in a whorl around a short, almost indiscernible stem. At the very top of the stem, in the centre of the whorl, is a microscopic growing tip from which the leaves are initiated. And as long as the tip produces leaves, the whorl remains intact, and the plant is said to be in a vegetative state.

Mizuna var. Broadleaved plant in the vegetative stage Yukina in the vegetative state

Two Oriental brassicas – Broadleaved Mizuna (left) and Yukina Savoy (right) – in the vegetative state. Note the whorl of leaves.

Unfortunately, the vegetative state doesn’t last forever, and at some point a trigger – such as cold weather, water stress or age – stimulates the growing tip to stop producing leaves and switches to developing a flower head. The plant is then said to be in the reproductive state. When this happens, the plant undergoes some visible changes:

  • The short stem below the growing tip starts to stretch upwards like a car antennae, and the leaves attached to it then become spaced more or less equidistance along its length.
  • A flower head develops, first noticeable as tight buds. 
  • As the stem gets longer, the flower head is lifted upwards, and the tight buds open out into flowers, followed in due course by the formation of seeds.

bolted stem of mustard Bolted tatsoi plant showing the flower

Left: Mustard plant showing elongated stem with the leaves arranged more or less equidistance along its length. Right: The flowering head of tatsoi var. Yukina Savoy.


The dual nature of bolting

Bolting is either good or bad, depending on who is doing the growing. From a gardener’s point of view, bolting is bad since the productivity of both leafy and root vegetables is brought to an end. From a seed producer’s perspective, however, bolting is good since the end product is seed, without which there would be no vegetable gardening. In the end, we all need bolting, just as long as it is delayed long enough for us gardeners to get some vegetables to harvest.


© Michael Michaud

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