Garden Clippings for August 18, 2018
Photothermoperiodic. I learned a new word last week. Actually, I learned it in Dutch and found the English translation for it at the time of writing this week’s Garden Clippings.
My cousin, Henk DeGroot, recently retired from DeGroot en Slot BV gets credit for teaching me the definition of photothermoperiodic, which is a term used to describe how a plant is sensitive to both daylight and temperature.
Henk knows all about photothermoperiodic, because he, along with several other relatives on my Dad’s side, runs one of the world’s foremost onion seed businesses.
About 65 years ago, soon after my parents made the decision to emigrate to Canada, Dad’s two brothers and one brother in law broke tradition in their small town of Broek op Langedijk by slowly switching from growing cabbage to producing onion seed. The company grew steadily and soon they were shipping onion seed beyond Holland to the rest of Europe. But when they tried shipping their quality seeds to India, the Americas, and throughout the world, they realized that onions were photothermoperiodic which meant onions grown in Holland at 52.6 degrees latitude won’t perform well in places like Toronto at 43 degrees, Sarnia at 42.9 and Rome, Italy at 42 degrees.
For onions, growth is mostly about day length. The further north you go, the greater the summertime day length. Most other vegetables don’t really care about day length. Planting a Beefsteak tomato in Toronto will give you the same success as planting in Whitehorse which has a latitude of 61 degrees.
Growing onion from seed is a two-year process. In our region, seeds are usually sown in fall. Sprouting will begin in 7 to 10 days and leaf production begins. Small bulbs, about the size of a marble will begin to form. Onions are frost tolerant. In spring, leaves will continue to grow, but bulbs won’t begin forming until temperature reaches 15 degrees C, and day length is 13 to 14 hours.
If growing onions from seed sounds too complicated, just buy the small onion bulbs (setts) first thing in spring. Soon after planting they will produce stems and once the days are long enough, they will put their energy into bulb formation.
If planting setts, mark out a little furrow in the soil bed and plant about half inch deep, so the tops are still visible. Mix a phosphorous rich fertilizer such as bone meal into the soil. Space the small bulbs about 4 inches apart. Onions like moisture, so add water during periods of no rainfall.
Onions can be harvested anytime after planting. In spring the stems or leaves can be eaten as scallions, and in summer the mild flavoured bulbs can be eaten. By the end of summer, bulbs will have their most distinctive flavour.