Autumn Will Soon Tip Into Winter. The Ten Hour Tipping Point Is When The Lack Of Daylight Limits Plant Growth With A Ten Hour Daylight Limit That Severely Limits Growth . It Starts on Oct 26th.

Ten Hour Tipping Point   Sunshine in a forest
Ten Hour Tipping Point   Sunshine in a forest

Of course the ten hour tipping point is just a simple way to remember the fact that less light means less growth. Plant growth is dependent on light for plants to photosynthesise and, all other things being equal, more light means more photosynthesise and less light sees a reduction in growth. And that means that we dont see lots of growth one day and none when the ten hour tipping point is reached. In reality its a tapering off of growth. But it is true that most plants fail to make significant growth when theres less than ten hours light per day.

“Day“ Length in 2022-23

In 2022, on October 26th, daylight is for ten hours and one minute in my area. Sunrise is at 7:43am and sunset at 17:54pm.

The day with least daylight will be December 22nd, though theres only one second difference with the 21st. At this time daylight hours last for 7 hours 49 minutes and 42 seconds. On February 15th we are back to a 10 hour and one minute day!

From the above you’ll note I talk about daylight length rather than day length as many people say this for ease. They talk about the days getting shorter, whereas the reality is that each day is roughly 24 hours long. But it depends how you define a day. By most measures each day is 23 hours, 59 minutes, 59.9997123 seconds (approxiamately 😀). But due to the tilt of the earth we lose, or gain, around 3.5-4 minutes of daylight a day, giving us the seasons. And that’s not the only complication.

Daylight Versus Sunlight – Sunny Versus Cloudy Days

I’ve talked about daylight hours as it that is all that mattered. But it isn’t. The reality is that light intensity matters as well. We get cloudy days and we get sunny days. And on a sunny day the plants get more energy from the sun, on an hour by hour basis, than on cloudy days.

So though a day might be longer, it might not be sunny, and this means less energy available for the plant to use in photosynthesis.

So the reality is that plants need both day length and light intensity to prosper. Plus of course they need all the other necessities such as warmth, moisture, nutrients etc.

Sunflowers following the sun
Sunflowers following the sun

Phototropism and Heliotropism

Many plants exhibit phototropism. I define it in my gardening dictionary as follows

“Phototropism is the directional growth process in plants where they respond to light. Positive tropism is seen when leaves, stems and to much lesser extent branches, grow towards the light. Roots often demonstrate a negative phototropism response.  

Heliotropism is an associated process but is not primarily governed by phototropism.”

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Tag; Ten Hour Tipping Point  

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