In The Garden


Last night, the man in the house remarked that it is getting darker. You’ve noticed that, right? Well, so have our plants. At least plants don’t suffer seasonal affective disorder ... or do they? Perhaps some do, in a way. Daylength (the number of hours of daylight each 24-hour cycle) does influence the successes and failures of many plants.

I remember a student once sighing because she missed the ‘white nights’ of her far north home village – 20 hours of sunlight at the summer solstice, I believe. Perhaps some plants yearn for that also.

Why is the Peace River Valley such a productive agricultural area for some crops? Well, it certainly isn’t their temperature, with an average annual temperature not much above freezing. The summer rain helps, but the real key is its scant seven hours of darkness each day. That doesn’t sound like much of a difference from us, but it can have a real impact.

A critical principle for both home gardeners and farmers is that daylength makes a difference to many plants. Actually, botanists have determined that it is the number of hours of darkness – not sunlight – that some plants are sensitive to. However, the term “daylength” was already in common gardening parlance before they passed that fact on to us gardeners.

Why does daylength (or darklength if we want to coin a new but more accurate term) matter to many plants? Some short day species like broad beans, heirloom strawberry varieties, Christmas cactuses, chrysanthemums and asters are genetically programmed to flower (and subsequently fruit) only when days are short and nights are long.

Although each plant species has its own critical hours of darkness to begin formation of the structures that will eventually result in flowers, many seem fixated on 12 hours each day. We transition out of 12 hours of darkness at the spring equinox and then transition back at the autumn equinox. That means that dark-loving broad beans must be strapping adolescents beginning flower formation early in spring or at the beginning of autumn (in a location protected from frost).

So if you want a fava bean crop next year, you need to start the seeds this autumn or very early next year, and grow them protected from killing frosts. Plant them in summer, and they will be mature and healthy enough to bloom. But with fewer than 12 hours of darkness each night, you won’t get many flowers or beans.

Want to force the issue when you forget all this and end up planting them next May? You’ll need to encourage flower formation by providing dense shade for at least part of the day. Seems like too much trouble to me. The short message: if you want blooms and not just a healthy plant, hustle a short day plant to maturity before the spring equinox. Think of short day plants as the vampires of the plant world.

Happily, most of our garden plants are long day species, genetically programmed to begin setting flowers when darkness is in scant supply ... the happy sun-loving flowers of the plant kingdom for whom darkness is the abhorred absence of life-giving sunlight. Plant these in mid to late spring so that they will be forming flower structures near the summer solstice, which happens to be when we relish being outside in the garden.

The only problem with long day plants is that many of our favorite herbs and vegetables are long day plants, and so set flowers (bolt) when nights are short. Lettuce, cilantro, spinach, radishes ... they all pour their energy into flowering as the white nights approach. Plant these early in spring to get an early harvest, forget about midsummer planting, and then plant them again in late summer for an autumn harvest. Your dining table will be happier.

Day neutral plants are happily oblivious to daylength, so we can plant them in spring and they will bloom or bolt on their own internal clock. That’s pretty much true of tomatoes, although our climate is not ideal for growing large-fruited tomatoes. And it is true of many garden flowers. Horticulturalists have put effort into developing day neutral cultivars so that nurseries can sell their seeds and plants to a wide clientele from subtropical to far north gardeners. That’s how we got some day neutral strawberries that will flower and fruit on and off – sometimes from June right through until early autumn. UC Davis alone has patented eight-day neutral strawberry cultivars, some of which, like Albion, are available to home gardeners.

If you don’t want to research which plants are day and night lovers, I suggest that you go online to find West Coast Seeds’ planting guides for B.C. coastal gardens. They’ve done the research for you, and have even factored temperature into account. How cool is that?


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