Vegetable Garden

What does it mean when your vegetables are ‘bolting’?

September 29, 2012
onion flower

Onion (Allium) Flower

When you’re involved in gardening it’s very easy to forget that simple terms we use on a day-to-day basis might as well be written or spoken in another language to non-gardeners. A question I’ve been asked a few times recently is “What’s a bolting vegetable?”, followed by “Why does it do that?” and “Can I stop it happening?”. As several of my plants are currently bolting, or in other terms ‘going to seed’, it seems like a good time to explain.

What is Bolting?

Visions of carrots uprooting, donning Lycra and sprinting across fields aside, the term bolting is used to describe plants that are starting to flower prematurely – or in other words before we’d like them to. Many plants can be affected – this year I’ve seen lettuce, spinach, cauliflower, kale, chard and onions produce flowers much earlier than we would have liked.

Parsley Flowers

Parsley Flowers

What causes Bolting?

Vegetable plants will turn to seed automatically when their life cycle is coming to an end – it’s their natural state to want to reproduce and spread their seed before they die. However, if they become stressed they may produce flowers much earlier.

Another reason is that some plants (radish, lettuce and spinach for instance) are sensitive to the lengthening daylight hours and will take the opportunity to start producing flowers.

How do plants become ‘stressed’?

So what causes our onions to throw out long stems with pretty pompom flowers on top or our kale to develop delicate yellow flowers that the bees and hoverflies adore?

Unsettled weather conditions are a prime cause of stress that will cause bolting and 2012 gave us a good example.

Chive Flower

Chive Flower

We experienced a mild winter which continued into early spring. This was followed by a couple of weeks of lovely warm weather at a time many of us were sowing our seeds – if memory serves me correctly the end of May was a bit of scorcher (by Irish standards) and under normal circumstances would have been the prime direct sowing time for many plants. However, by early June the warm days continued (albeit quite damp) but night-time temperatures plunged, almost to zero on a few occasions. These fluctuations in temperature would have been enough to stress developing seedlings.

Another stress factor might include dry soil – a result of warm days and erratic watering which can be avoided once you’re aware of it.

Kale Flowers

Kale Flowers

Can we stop bolting?

We can certainly delay it. As soon as you spot a thick stem starting to appear in the middle of your onion plant, snap it off – if you allow it to continue it will put all its energy into producing a flower and not into developing an onion bulb as can be seen in the example below. If you notice kale developing flowers rather than leaves, snap them off too.

An onion that has been allowed to flower ~ at the expense of a large bulb

An onion that has been allowed to flower ~ at the expense of a large bulb

You can buy bolt resistant seeds for vegetables that are prone to it – there’s a popular variety of beetroot for instance called ‘Boltardy’.

Starting seedlings off in modules and planting them out once temperatures have settled often helps (although this year may have proved the exception).

Ensure your soil is in good condition. If it is, your plants will be stronger, grow faster and you’ll be harvesting them earlier, often before they’ve had a chance to become weather stressed or succumbed to the lengthening days.

Is there anything else I can do?

It might be worth remembering that many vegetable flowers are not only beautiful but edible too. There’s a lovely article here in the State-by-State Gardening Newsletter that has images of some very pretty vegetable flower arrangements. Here’s an example of one I like that is totally edible containing flowers from kale, fennel, verbena, rocket, peas, onion, beet and chard:

Edible Bouquet

Photo credit: Cindy Shapton,

Did you notice an increase in bolting this year or have you made flower arrangements from vegetable flowers? I’m heading out now to pick a few kitchen garden flowers for my table that I mightn’t have thought of before. If you can’t afford to buy cut flowers on a regular basis, perhaps you need look no further than your own garden or hedgerow…



  • Reply Brian (@_secretgarden_) September 30, 2012 at 6:29 pm

    A popular topic at today’s talk…..and I will be giving people this link as your post clearly explains what causes bolting and how to delay and embrace it.

    • Reply greensideupveg September 30, 2012 at 7:04 pm

      Thanks for that Brian and hope you had a good crowd today for the talk. It’s great to hear that garden centres are educating as well as selling their products 🙂

  • Reply ayearinredwood September 30, 2012 at 6:47 pm

    Dee, I’ve been using ‘bolted’ broccoli flowers and others in flower arrangements for the church!

    • Reply greensideupveg September 30, 2012 at 7:11 pm

      Yeay, that’s great to hear Margaret! My kale is more yellow flowers than green or red leaves at the moment so may just go and snip them off now and fill a few vases


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