Why does my Coriander bolt to seed?

Last Sunday my son, Ben and I spent the day at the Frankston Toy Library’s Teddy Bear’s picnic. Fortunately it didn’t get too hot. Ben and I run a free “pot a plant” stall. At community days they usually have the petting zoo, which Ben loves and I let him sell off surplus plants to the parents who can’t help themselves. Sadly Ben has had a lesson in free market economics this weekend; he has at previous fetes pocketed as much as $100.00 which is immediately blown on computer games or Lego. On Sunday, with the nursery industry in the doldrums he took less than $20.00 (and I am too mean to pay for his services). We potted flowers and vegies all day with the kids, but their parents just were not interested in buying this time.
Any way, I like potting days because I meet gardeners and I can work on building our newsletter mailing list. The standout question from the weekend was, “Why do my vegies bolt to seed?” On the spot I found this difficult to answer properly and having done a little research I know why. This is a common symptom but the reasons vary depending on the vegetable variety.
Let’s focus on Coriander today.
Coriander is from the Carrot and Parsley family. It originates from southern Europe and the Middle East and is widely grown and used throughout Asia. You would imagine that it likes hot weather. However, Coriander is a classic annual. If it is stressed its first priority is to set seed and ensure the survival of the next generation. In its natural Mediterranean environment stress is most likely to come from heat, so extreme heat is a common trigger for Coriander bolting to seed.
How do you prevent this? Minimize plant stress. Provide light or dappled shade in the hottest part of summer, make sure plants are well watered and take extra care transplanting. Many sources recommend direct seeding to prevent transplant shock. Of course I would prefer that you didn’t use this option and remind you that direct seeding is fine, as long as you get good germination! Germinating can be the trickiest part of the job.
By the way, a number of people have suggested just cutting the flower stem out and continuing to pick the leaves. Another thought is to pick the stem before the flowers open. The stem is very flavorsome (actually this suggestion was for Bok Choi, so if Coriander tastes terrible I’m sorry).