Publications (Paul's Blog)

September 13, 2011

Filed under: Uncategorized — Paul Dowlearn @ 3:20 pm


Having been in the landscape and nursery business for many years, I have learned to compare plants and humans. There are many good correlations and analogies that work. Since even non-gardeners understand human physiology to some extent. This tactic works well to help folks understand plants better. However, when it comes to heat plants are entirely different from humans. Plants love it!
Somewhere around 90 to 95 degrees we humans begin to feel stressed, especially in high humidity. At 100 degrees, most of us are making good use of outdoor shade and are extremely grateful for indoor air conditioning. Heat makes us lethargic and cranky. Unfortunately as we get older our ability to withstand heat becomes diminished. Even young folks can have serious problems from too much sun.
Because of this, people seem to think that plants that are in full sun or that are planted (God forbid) on the west side of a structure need to be especially heat tolerant. For sure there are some exceptions. Heat is not conducive to cool season annuals or some of the plants better suited to northern climates. You certainly should not plant shade loving woodland plants in the sun. Maybe somewhere in the northeastern United States you could plant say, a hydrangea in full sun with western exposure. Not in my part of Texas. That hydrangea better be in shade from midday on. These exceptions aside, it really doesn’t matter because most plants love heat.
Think about it. Didn’t we invent the edger to keep the grass off of the sidewalk? Of course we did. That same sidewalk on a hot summer day may reach temperatures in excess of 200 degrees. Did we not melt our crayolas or actually fry an egg when we were kids? Sure we did. I can remember kids on my block seeing who could stand barefoot on the asphalt the longest. If heat was a problem for plants then shouldn’t they shrink away from these areas? No sir, you see plants growing through the cracks in asphalt all the time.
One more fact, as we look at our planet we find the most heavily vegetated areas to be near the equator and adjacent tropics. This part of the planet is hot or at least warm all the time. There is no winter in the tropics. There are so many plants in the tropics that I’ve heard it said a good botanist will find a dozen new species………….on the first day! So it is obvious that plants respond favorably to heat as long as adequate moisture is available. And that, my friends is the key,
Perhaps you have heard the rain forests of Africa and South America referred to as the “lungs” of our planet. As the moisture contained in all these plants transpires it creates a perpetual cycle of rain that forms during daytime heating. In fact, the tropical storms that affect our Texas coast actually start out as a puff of moisture from the rain forests of Africa that gets carried out to sea. As this disturbance moves across the Atlantic Ocean it feeds off the warm water, gaining moisture until it becomes a tropical storm or full blown hurricane. The same thing happens in the Pacific from moisture produced in tropical South America.
So heat is not the enemy. It is instead lack of moisture. Humidity, morning dew, fog, and rainfall keep plants hydrated as heat simply speeds up the growth rate. Without adequate moisture, the plant will slow its growth rate and begin to shed older leaves to conserve moisture. As drying continues, the plant will wilt, then finally die. Unfortunately, in the western two thirds of Texas, our hottest part of the year is also typically dry. Low humidity combined with hot southerly winds, few (if any) isolated showers, no morning dew or fog can spell disaster for any new plantings. Even in shady locations. Make no mistake about it.
This is why we recommend native and well adapted plants. Emphasis should be on drought tolerance for the western two thirds of the state. Be aware that true drought tolerance does not kick in until after the plant has become established. I think this may be one reason that some folks have trouble in hot locations. On a hot summer day evaporation rates may surpass the equivalent of ¼” of rain per day. Most people plant in the Spring when the weather is favorable. Then along comes Summer, just when our homeowner is most reluctant to venture outdoors. The rain quits, things begin to dry out, and the inevitable happens.
East side, west side, full sun, or partial shade, we should always keep the dry days of summer in mind. This does not mean you should have to settle for cacti or some other desert flora to take that reflected heat of a south or west wall. Just remember that those plants that catch that reflected heat will dry out faster. If you are using the right kind of plant material then which side of the house you are planting should not matter unless we are talking deep shade. Don’t forget that a shade lover planted in the sun is toast…………..Regardless.
So many people come into the nursery and describe the time of day that their intended spot gets sun. In truth, any time after 10 AM until 7 PM is hot and the Summer sun is intense. Anything beyond four hours of midday sun would be considered full sun in Texas. Most plants will thrive in that sun provided they have adequate moisture. Even a prickly pear will appreciate a bit of help during a serious Texas drought.
I know that far too often those of us in the landscaping business tend to get carried away when proclaiming the ease of growing the plants we know do well in our respective areas. I also realize that some people take everything said as gospel. They want a schedule, easy procedure, and simple instructions. Experienced gardeners know that you must water according to the weather. No schedule can match our roller coaster weather. Watering every day doesn’t work either. The leading cause of plant death is not the heat of summer, or the cold of winter for that matter. It is too much, or too little……………….water!

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