Post date: Apr 1, 2020 1:35:53 PM
We spoke so much about coriander recently. Why can’t it be grown in the summer?
Plants have two distinct phases of growth: the regenerative stage where they sprout leaves and branches; and the reproductive stage when they form flowers and fruits.
Regenerative stage goes on unhindered, except when day length drops below 10 hours. At this time, the plants simply stall and do nothing. We call this the Persephone and in Atlanta this phase is between Dec 9 and Jan 9, usually. Gardner’s can take a true break from work :)
Back to the coriander. The reproductive stage depends primarily on day length. When a plant will send out flowers depends squarely on how much darkness it enjoys. Yes, not light, but dark!
The technical term is photoperiodism. Or in simple
terms seasonality. Coriander is a long day plant. That means, when length of day goes above length of night (March 21 equinox) it will produce flowers. We call it bolting.
Here are some notes:
1. Photoperiodism refers to the amount of light and dark a plant is exposed to. It was earlier thought that the amount of light was critical to a plant. Research then showed that how much of darkness a plant experienced was critical to flowering and fruiting.
2. Plants are classified as short-day, neutral-day and long-day plants. A short-day plant, like avarekkai, will begin to flower and fruit only when the length of the day is shorter than the length of the night. Post Sep 21 equinox is the season for Avarekkai.
3. A long-day plant will flower only when the length of the day is longer than that of the night. Those of us who planted bhendi in the winter know what a disaster that turned out to be. Post March 21 equinox is the time for the long-day plants.
4. Neutral day plants don't care much, and are quite fine flowering and fruiting through the year. Corn and tomatoes are examples of neutral day plants.
5. Spinach and coriander thrive in the winter. But in summer, they simply bolt and flower, because they are actually long-day plants whose trigger to flower and fruit is set off when the day gets longer.
6. Research has shown that ensuring the required number of hours of darkness can enhance the productivity of plants. Turning the decorative lights off at night helped one of the gardens I set up to become productive :)
7. Plants have an internal calculator that is sensing the length of light and dark, and the flowering and fruiting happens based on this intelligence. We cannot get a poinsettia to burst in red in the summer, and nor can we get a azalea to bloom in the winter!
8. Eating seasonal food is based on a similar intelligence applied to the human body. Vegetables and fruits that grow in the summer hold water that the body requires to fight the heat, while winter crops hold sugars and starch to enable higher metabolism to keep warm.
Time to fight that urge to grow and eat all kinds of food all year round and align with the amazing intelligence of plants. If you are a commercial grower, you will invest in greenhouses that come with shades to modify dark hours for the plant. Store bought corianders have been this fooled for years into thinking that nights are longer than days forever!
Note: I posted a version of this note at the Organic Terrace Gardening FB group 5 years ago. This note revises the example for the Atlanta gardeners.