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.

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