Publications (Paul's Blog)

August 25, 2009

HEAT

Filed under: Uncategorized — Paul Dowlearn @ 7:00 pm

Always a good topic during summer. It’s a pretty safe bet to go ahead and predict a hot one. When it gets over 90 degrees, humans don’t like heat much. It makes us cranky, sweaty, and lethargic. About the only thing worth the effort of getting out in it is the prospect of icing down some beverages and heading to the swimming hole. However this is the time when our plants need us most. Even a mesquite will appreciate an occasional deep watering when the heat is on. No wonder that summer is the time when most landscape plants die.

Oddly enough, if we study the tropics we find that they also have 100 degree plus days (sometimes in excess of 120) whenever the earth tilts that particular piece of real estate closer to the sun yet these are the most heavily vegetated areas of our planet. Apparently plants respond favorably to heat. The difference between a tropical forest and a desert is actually moisture. So from this we can logically assume that heat is not our enemy when it comes to plant life, instead it is the lack of moisture.

Another obvious example is the greenhouse (also called a hothouse).On a cool spring day you can walk into a greenhouse and immediately feel the difference in temperature. Greenhouses are designed to increase heat and trap humidity. By mid spring here in Texas most greenhouse owners will have an exhaust system in operation to keep the place from turning into a steam bath. If you’ll check the thermometer recording inside a greenhouse you will find that it is not uncommon to see readings above 120 degrees yet the plants are loving it.

Okay……….now I can imagine most of you are saying you will just water more during summer and everything will flourish…….Right? Watering will be a great help but there are two other factors that are working against us. Humidity is the measure of moisture that is carried in the air. We can increase the humidity as we water but that increase will be short lived. Early morning is the best time to do this. Plants will open their stomata (breathing pores) to exhale oxygen and inhale carbon dioxide in the morning when humidity is at its highest and the temperature at its lowest. However by noon evaporation will have dried any residual moisture so we are now dealing with whatever humidity levels are present for that day. Wind speed also plays a big part in evaporation rates. Wind speeds are generally at their highest during the peak heat of the afternoon. This is also when humidity tends to be lowest. Here in North Central Texas we typically lose the equivalent of 1/4 inch of rain per day during summer. During a serious dry spell with southwesterly winds blowing 20 to 30 mph combined with 15% humidity and temps at 105 or more we can easily lose 1 inch or more daily. You can imagine what a tremendous amount of water it would take to offset this. Here’s some things you should do.

Select native and drought tolerant species. This is by far the most important thing you can do to survive a serious heat wave. Check out the plants that live in your part of the state. See what Nature provides. You will likely notice that there aren’t many plants with great big leaves. Instead you will see that most native plants sport smaller or thinner leaf structures. The growth can be lush and the blooms abundant but the plant must be thrifty to survive Texas summers. Some plants will have silver, gray, or white foliage to reflect heat. Others may sport green stems that produce chlorophyll even when leaves are not present. In the case of cacti and succulents, the entire above ground surface can photosynthesize. Many plants store water and nutrients in fleshy leaves, bulbs, and tubers. These plants not only survive but many actually wait until hot weather to bloom and some will bloom all summer long.

Am I saying that it is not a good idea to have a landscape full of broad leaved tropical plants? Exactly right, unless you live on the Gulf Coast. Even though tropicals thrive in heat they will require water and plenty of it. On the other hand, growing an elephant ear or a banana tree can be fun so if you have a fetish for this sort of thing, try to keep it limited but go ahead and experiment. Am I saying that to live in Texas you should rely on desert plants? Absolutely not, unless you live in the desert. Most of us live in places that support lush vegetation. There are many native and well adapted plants that will survive with little or no care given normal rainfall. Use them for the bulk of your ornamental displays.
Compost Compost improves the water and nutrient holding capacity of all soils. It is the perfect “fertilizer” for any and all plants. Add to the top of lawns and existing plant beds. Incorporate into the top layer of new plantings. Just do it.

Water wise. An occasional good deep soaking is what most woody and flowering plants require. This can be supplied with a simple slow trickle from the water hose laid about in various places. However the ultimate in irrigation technology is drip. Drip is far superior to soaker hoses and can be used with automatic timers and underground moisture sensors to create a true hands off “set it and forget it” type system. Pop-up spray heads and conventional sprinklers are slowly but surely becoming obsolete. Too much water is wasted due to runoff and evaporation. Mulch Bare soil heats up and dries out quickly. Even rock or gravel will help reflect heat and conserve moisture. Organic mulches (leaves, straw, shredded wood, etc.) will eventually break down to feed the soil. This is an integral part of the life/death/decay/new life cycle and is the absolute best thing for most forms of plant life.

Most of us have marveled at the plant that manages to grow in a crack of our concrete or asphalt. We wonder how a thing could grow in such a hot and hostile environment. Yet when you consider the facts, underneath that asphalt is a cool moist environment, plus the asphalt acts as a mulch to absorb and reflect the heat. Most plants just love that sort of arrangement. If you have ever tried to kill weeds growing in a parking lot you know what I’m talking about. While you and I will begin to wilt in high humidity, with no breeze, and temps above 90 degrees, plants will flourish. Get out in the early morning and check things out. Water as necessary to offset rainfall or the lack thereof. Put plenty of compost on everything and top it off with a layer of mulch. With any luck at all you should be done and back in the air conditioning by noon.

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