WHAT CAUSES BOLTING IN PLANTS?
Submitted by ~ Sheri Kisch
I had planned to answer this question, plain and simply. Bolting in any plant is not plain or simple. I and others just want to know why the spinach is bolting at 2” tall and another year it doesn’t bolt till July. And what’s up with mums in full bloom in July?
“Bolting is the premature production of flowers, especially of vegetables usually triggered by environmental or cultivation factors” according to the Dictionary of Gardening.
That being said I found that many things rule bolting in plants. To start, it can be induced by plant hormones. Really! Gibberellin regulates different developmental processes that include germination, stem elongation, dormancy, flowering and flower development. When plants are exposed to chilly temperatures more GA’s are produced. You can see how cold wet spring weather can start the process.
Bolting can sometimes occur from changes in day-length called photoperiodism. The critical day length for spinach is 13 hours. So when I planted seed in May, I would already be behind as the May day-length is at 14 hours. My row of spinach that was left to seed on purpose, then chopped up and turned under for mulch. It started growing last fall. It was very hardy – but – it was also very cold with a rainy spring that triggered the GA’s which in turn started senescence. The plants already had small flowers forming at 2” high. You can find calendars and charts online that give day length and critical hours. Scientists have long thought it was the length of daylight that made differences in plants. They have now found that the amount of complete darkness is what makes the most difference.
Take a deep breath. Ok, you have heard about planting by the moon. We now go into a whole other realm. Root crops are planted in the dark of the moon and above ground vegetables are to be planted in the light of the moon. The moon controls gravity, which influences soil and water. The Old Farmer’s Almanac is a good source of information.
Senescence is the aging process of a plant or part of a plant. Trees are a good example of senescence because of the amount of leaves changing color and falling off, dying. Sometimes it’s a natural process or it can be caused by environmental factors such as day length and season change. It can be triggered on only part of the plant due to pests, disease or drought. The plant can shut down the part that is diseased to save the whole plant or tree and prevent disease from spreading. All natural senescence is regulated by hormones.
There is so much more about bolting for me to learn and tons of information out there. Using your favorite search engine, type in bolting, photoperiod, day-length, moon phases, or senescence. This is where level 2 & 3 come in laying the ground work. Dara Palmer gave me some good extension websites.