Gardeners are ‘light farmers’
When it comes to plant growth gardeners often think in terms of temperatures rather than daylight hours.
Temperatures do have a bearing on growth as warm soil and midrange temperatures between 20 to 30 degrees certainly assist growth, but it’s the amount of sunlight or even artificial light a plant receives that makes the real difference.
It was a common nursery practice to increase the amount of light hours some plants receive in the early or late part of the season by having lights in glasshouses.
In winter, lights were timed to turn on at 6am for about 2-3 hours and again at 4pm until 9pm. Instead of eight hours or so natural daylight, plants were receiving 15 light hours. These additional hours of light caused buds to form and flower much earlier than otherwise.
It’s the increasing daylight hours at this time that is initiating dormant deciduous roses and trees to open their flower and leaf buds.
A gardener from Twizel asked if these articles could be adjusted for New Zealand’s seasonal differences; the season he says is much shorter in Twizel than say Auckland.
Actually, the growing season is not as short as he thought in terms of the daylight hours southern gardeners have available.
On New Year’s Day, the sun rises in Auckland at 06.05am and sets at 08.43pm. In Invercargill it rises at 05.51am and sets at 09.31pm. That gives the southerners an extra hour and two minutes of sunlight.
In winter on June 20, the sun in Auckland rises at 07.33am and sets at 05.11pm. In Invercargill it rises at 08.20am and sets at 04.59pm – a loss of 1 hour and 9 minutes of sunlight.
This doesn’t matter all that much because winter cold means not too much is growing anyway. It’s the extra hour in the middle of summer during the growing time that is vital.
In Alaska where there are six months of darkness and six months of sunlight, a plant can reach maturity in the three months of 24/7 daylight that would take six months to grow here.
Cold southern winters reducing bug and disease problems, and the added sunlight hour in summer are the envy of northern gardeners.
An email I received summed things up nicely: ‘‘I think the fundamental shift in thinking that we have to make is that farming is about harvesting light.
‘‘Through the process of photosynthesis we’re changing light energy into biochemical energy, and that biochemical energy becomes our plants, our animals, and the carbon compounds that are made by that process.
‘‘We are fundamentally light farmers and when we make that realisation, the sky’s the limit.’’
Then there are what are known as microclimates. A gardener with a microclimate may be a month ahead of someone just down the street. For example, a nursery on the outskirts of Palmerston North has a growing-on/holding area for young plants at the bottom of an old gravel pit. The stone sides of the pit not only provide shelter from the wind, they retain a higher temperature than the surrounding area making for better growth.
Warmth and light are two essential ingredients for promoting growth.