hours of sunlight

Seasons In The Sun

Seasons In The Sun

By Lois Hole

Originally Published in the summer of 1998, the following article highlights Lois Hole's respect for the natural change of seasons and her acknowledgment that no garden is eternal and unchanging. As she describes, the passing of seasons – while daunting for some -- is just one more beautiful reason to enjoy gardening.

A friend of mine had always grown wonderful tomatoes in her backyard. She loved their fresh taste and the satisfaction she got from growing the plants herself. Over the years, however, she noticed that the flavour of her tomatoes gradually began to diminish. She hadn’t changed her watering or fertilizing practices, and she was planting the same varieties year after year, so the reason for the change was elusive.

My friend also had several trees in her backyard. She finally noticed that as her trees grew, they were shading out the tomato patch. The tomatoes were being deprived of their crucial source of energy—the sun’s rays—and that was enough to rob the tomatoes of their flavour. Such stories remind me that the sun has the most profound influence in the garden. Success in the garden ultimately revolves around the sun.

Just out of curiosity, I pulled out my copy of Climates of Canada to see how summer sunlight levels vary across the country, since day length is one of the ways that the sun affects plant growth. Many people are surprised to learn that corn will grow in Yellowknife, despite its rather short growing season. This is possible because northern areas have many more hours per day of sunlight, which somewhat offsets the cooler temperatures in these regions. Although the average frost-free period in Yellowknife is only 111 days, on June 15 the sun rises at 2:45 am and sets at 10:30 pm! Compare the average hours of sunlight between Yellowknife and Toronto: the southern city receives a little over 1000 hours of sunlight during July, while Yellowknife gets almost 1400 hours of sun. It’s no wonder that cabbages of monstrous size are often grown in the Territories, since those long days allow the leaves to use more sunlight, which generates more growth. The same sort of effect happens in Peace River, in northern Alberta: corn grown there will mature only a few days later than corn grown in Medicine Hat, close to the US border—even though the corn in Peace River gets planted much later! I have friends in both communities who grow vegetables, and it’s interesting to watch the friendly competition between north and south: whose crops will mature first? The south usually wins, but it is by no means a foregone conclusion.

The same combination of long days and cool temperatures creates the most vibrant flower colours, too, and long days can boost flower production. Snapdragons, for example, often enjoy an increase in flower numbers as the day’s length increases. Flower stalks that mature in June are about one-third longer than those that mature later in the season.

As you might suspect, low light levels tend to have adverse effects on nearly all plants. Fruit flavour can deteriorate quite noticeably under these conditions; tomatoes that get less than six hours of sunlight per day may taste mealy and unpleasant, and the sharp tang of apples won’t develop without plenty of bright sunlight. Most flowering plants won’t bloom at all if there isn’t enough light. Mandevilla, for example, is a gorgeous vine that produces pink, trumpet-shaped flowers, but it needs to accumulate a lot of energy from the sun’s rays before it will even consider producing flower buds.

However, too much sun can be just as bad as too little. Sunscald—the plant version of a sunburn – is a concern right across the country on hot, bright days. Plants affected by sunscald develop pale-yellow or greyish white patches on their leaves or fruit. This often happens when the plants are in a location that reflects the sun’s rays, such as next to a white stucco wall. I’ve had the fruit of my pepper and tomato plants burned badly by reflected light, so I’ve learned to plant them where this won’t happen; next to a darker-coloured wall, for example.

One danger, though, is exaggerated. According to a commonly held belief, you shouldn’t water on really hot days because water droplets on the leaves will magnify the sun’s rays and burn the plant. I can’t tell you how many times I’ve heard this, from friends, professional growers’ magazines, and even community-service bulletins. But think about it for a minute: we often get bursts of rain followed by intense sun. I’ve never noticed hundreds of holes or burn marks on my trees or on the grass. In all my years of watering, I’ve seen no evidence of water droplets searing leaves or fruit. Perhaps this notion came about because pouring cold water on plants like African violets can sometimes cause chilling injury. White spots appear on leaves and flowers because of the sudden cold shock, but sunlight is not to blame.

There’s not much we can do about day length or the sun’s intensity, of course, but we can breed varieties that are adapted to these conditions. Strawberries, for example, typically bear fruit in June, when the days are longest. There are everbearing varieties as well, which bear mostly in June, but also sporadically through the course of the summer. The newest varieties of strawberry are the day neutrals. These plants are not influenced by day length and so bear fruit heavily from July until the first frost. Day neutrals were developed by crossing and back-crossing June-bearing types with a wild everbearing strawberry found in the mountains of Utah. (“Back-crossing” is the process of crossing hybrid varieties with original, heirloom cultivars.) The result is a vigorous plant that bears fruit much longer and much less sporadically than other varieties. I switched to the ‘Tri-Star’ day-neutral variety several years ago, and the difference in yield and flavour has been just tremendous. I always look forward to seeing what kinds of new varieties will be tested in our trial gardens; many of these, like the day- neutral strawberries, will be able to make more efficient use of the sun’s energy.

Keeping the sun in mind will give you a big leg up in your pursuit of the perfect garden. As the Beatles used to say...here comes the sun, and it’s all right.