Growing in the Kootenays

Daylight Hours

Castlegar was chosen as the chart, because the data is easily accessible. The length of daylight our regions southern boundary (around Creston) and the northern boundary (around Nakusp) is about 4 minutes in winter and around 10 minutes in summer, so for all intents and purposes, the chart would remain the same for all areas of the Kootenays.

Light - General Information

The sun emits a wide range of radiation. The light we see is called visible light. It is a small segment of all the radiant energy given off by the sun. Visible light is what drives photosynthesis. Some other types of radiation are X-rays, gamma rays, ultraviolet rays, microwaves, and radio waves. Radiation travels in waves. The wavelengths of the different rays are measured in nanometers. Based on their wavelengths, the rays have been placed on an electromagnetic spectrum.

Light Colour

Sunlight contains a complete blend of visible colors, including red, orange, yellow, green, blue, and violet. Plants need mostly blue and red to activate their chlorophyll. Other pigments collect other colors of light and pass that energy to the chlorophyll to make more sugar. Different colors of light solicit different plant responses.

Red and blue light have the greatest impact on plant growth. Red light promotes seed germination, seedling growth, and stem elongation. Red wavelengths also influence flowering and the formation of anthocyanins (pigments in blue, red, and purple flowers). Blue light reduces

stem length, increases branching, and promotes stem strength. Blue light improves leaf and flower color, too. Far-red light triggers a shade-avoidance response in plants when levels of blue or red light are low. Stems stretch and become weak while leaves become thinner and wider. Far-red light also plays a key role in the breaking of seed dormancy and in photoperiod responses.

Light Intensity

Light intensity influences plant growth. Intensity of light depends largely on the angle of the sun and on clouds and dust in the atmosphere. Light intensity is greater in the summer months when the sun is higher in the sky.

Light intensity is measured in foot-candles. A foot-candle is the amount of light distributed by a single candle 1 foot away. A sunny summer day provides about 10,000 foot-candles of light. The high light intensity elevates the rate of photosynthesis, and plants are able to produce more food.

Plants receiving the optimal level of light will be compact and have good leaf color. Symptoms of lower than optimal light levels include a slower growth rate, thin leaves, small flowers, dull leaf and flower color, and etiolation, or stretching. Extended periods of cloud cover can slow crop growth and ultimately reduce yields.

Light Duration

Some plants are responsive to the length of time they are exposed to light. These plants have a photoreceptor, or light-sensitive pigment, that absorbs light. Phytochrome is a type of photoreceptor within plants that detects day lengths. The length of the days or the length of the light period is known to influence different phases of plant growth, such as flowering.

Other phases are seed germination, enlargement of leaves, and development of buds. The length of a plant’s daily light exposure is its photoperiod.

Plants can generally be separated into three groups based on their photoperiod response.

Short-day plants (SDP) are plants that begin to flower when the nights are more than 12 hours long. Long-day plants (LDP) are plants that begin to flower when the nights are less than 12 hours long. Day-neutral plants (DNP) are plants whose flowering response is unaffected by their photoperiod.

The 10 hours of daylight line.

Whether growing plans commercially or for your own use, it is important to recognize that there are times of the year that it is impossible to grow plants, irrespective of the temperature, because the availability of light is not there.

Generally for most vegetables, this cut off point between growth and non-growth at our latitude is 10 hours of daylight. This means that for part of October, November, December and January - there is insufficient light to support growth. This period may be extended by the presence of heavy cloud or valley cloud. In 2006, the valley cloud between Castlegar and Nelson was unbroken until the end of  March - and although the temperatures were above the level needed to allow growth - none took place.

So at the end of the growing season - harvest  everything you can by the end of October as there will be no growth until the next year.

For warm season crops such as tomatoes, peppers, cucumbers and eggplants look to finish with these by the middle to end of September. There will by this time, (middle of September) be insufficient light to support the plant and generate the sugars to ripen fruit.

For those who over winter vegetables such as spinach, even in a greenhouse, stop cutting or harvesting by the end of October to allow the plants to stabiles before going though the winter. If in a greenhouse, growth will commence again in February or March when harvesting can resume again .