Microclimates – What is that?

If you work in the tree tube business long enough, you use terminology on a daily basis that you yourself at the beginning didn’t completely understand. I have to remind myself that customers are sometimes hearing these terms for the first time or may not completely understand the term although they may act like they do. I used the term microclimate maybe 5 times this week and thought are my customers asking themselves “What is that?”

So everyone, except the southwest, is probably experiencing winter weather at this point in the year and in my tree tube nerdness I had an experience that mimicked what I feel a tree feels inside a tree tube. I was taking a hot shower this morning and when I pulled the shower curtain a bit to get my towel, a rush of cold air poured in and I quickly closed the curtain. How could I still be warm in the shower without the water running and yet it be so cold in the bathroom? I had created a microclimate inside my shower. Of course more than just temperature is happening inside the tube just as in the bathroom.

Plants breathe through tiny openings on the undersides of their leaves called stomata. Plants can (and do) open and close their stomata under certain conditions, for example if heat or wind becomes excessive and causes a plant to start loosing more water than it can take up, the plant will close it’s stomata to slow down the water loss. Unfortunately, by closing the stomata and slowing evaporation the plant also has slowed down it’s cooling mechanism. This causes heat to build up in the plant tissue, and if temperature becomes too hot the plant actually cooks itself. It is important to understand the opening and closing of the stomata and how it, in turn, controls plant transpiration.

Plant transpiration is how plants breath. Plants do not have lungs, however, so when molecules of gas and water vapor are released from the stomata they tend to just hang there in the absence of any breeze. That is why it is so important to have venting on the tubes to circulate the air (in addition to exhaust fans). This venting is actually like the plant’s lungs, and without them the plants would have no way of moving fresh CO2 molecules into contact with their plant tissue. The plants would slowly choke on their own transpired gasses and water vapor.

As water evaporates from the surfaces of leaves, the surface tension of the water molecules tend to pull the next water molecule along behind it, up through the plant’s veins. Water is pulled up through the plant stem, which is pulled from the plant’s roots. This creates a negative water pressure in the root zone and allows the roots to suck moisture up out of the root zone like a straw. The process of water absorbing into the plant through the roots is known as osmosis

Which brings me back to humidity. Water vapor is humidity. As a plant transpires, the humidity immediately surrounding the leaves will become saturated with water vapor. Now, the entire plant transpiration cycle is controlled by evaporation. When gasses surrounding a leaf become saturated with water vapor (100% humidity), there is no place for the next molecule of water vapor to evaporate to.

The end result is that water vapor is not evaporating, so water is not being drawn up from the root zone…and neither are any nutrients. If nutrients are not being taken up, than developing fruits are not getting the food they need to be healthy. This is exactly why high humidity will cause blossom end rot in fruiting tomatoes just like a Calcium deficiency. It is another reason why it is so important to have venting to keep the air circulating.

So, evaporation controls plant transpiration. High temperatures and low humidity therefore both cause fast transpiration. Fast transpiration means your plants will be taking up and using lots of water (and nutrients). Any of us living in the south and many in the north this past summer know all too well that we don’t get high temperatures and low humidity. We have high temps and high humidity, but the tubes help keep the trees in an environment that is most beneficial to growth.

This is why tree tubes work. They create low wind conditions to allow for plants to continue growing and to keep the stomata from closing. Basically on windy days, other trees have slowed growth down, but trees in tubes are wide open and growing. The venting controls transpiration which allows the tree to more efficiently use nutrients and water during high stress periods. The tubes have created a climate that other plantings don’t have. A microclimate.

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