I went to the pharmacy the other day to buy a thermometer.  I have a new baby boy and my wife and I wanted to be able to take his temperature.  From our daily weather forecasts to the news about climate change temperature is and integral part of our daily lives.  Understanding temperature is important and without all the instruments to measure it; we can turn to plants for help.  Plants tell us about temperature because every plant has something called hardiness.  Hardiness is the minimum temperature a plant can survive in before it dies.

Hardiness is broken into zones and is variable across regions and countries.  I live in the Luther Burbank Neighborhood in Santa Rosa, California and we are in zone 9, where the average minimum temperature is 30-20 degrees F.  Zone 9 is milder than my hometown in Connecticut where the average minimum temperature is 0-(-10) degrees F.  In my garden, plants behave in a particular way as they respond to temperature.  I grow pepper, broccoli and barley and each of these three plants tells a different story about temperature.

I grew a pepper plant all summer long and it is hardy above freezing temperatures.  When the temperature drops below 32 degress F, the pepper experiences a frost.  The water in its cells turns from liquid to solid.  Given that ice is less dense than water; the same amount of water when frozen takes up more space.  When the ice melts the next day, water rushes out of the plant cells and the pepper shows symptoms of permanent wilt before drying up.

Broccoli is typically grown as a annual plant when cultivated as a vegetable for supermarkets.  In my garden I am able to grow it as a perennial.  In the cool months, broccoli grows during the day and does very well at night even if the temperature drops below freezing.  But, it is only hardy to 20 degree F.  Broccoli tells us about temperature in summertime as well.

Unlike the pepper plant that thrives under temperatures as high as 90 degrees F; broccoli begins to wilt and look sick.  In order to keep my broccoli plant alive, I used a horticultural technique of removing leaves and watering to keep it alive until temperatures cooled down in autumn.  Understanding how the plant responds to temperature is how I was able to the same broccoli plants alive for over one year.

The final plant I want to talk about is barley. Barley is grown for grain and it is also used in crop rotations as an annual winter cover corp.  As summer turns to fall, farmers plant barley seed and barley only germinates at a specific temperature.  The seedlings grow to a certain height and during the cool season they slow their growth in order to survive the winter.  Barley begins to grow again during spring as the temperature warms up.  In my garden, I plant barley as a cover crop to add carbon to the soil and to break up compacted layers that I am too lazy to dig up.  I developed a strategy where I harvest the leaves and use them in my compost.

Different plants tell us different things about temperature.  Plants like pepper die at frost, broccoli survives under a wide temperature range, but only thrives in cool weather and barley follows a specific life cycle based on temperature.  I have one question for you .  What type of experiences have you had where plants told you something about your environment?

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Tags: cycles, garden, hardiness