Publications (Paul's Blog)

November 19, 2009


Filed under: Uncategorized — Paul Dowlearn @ 6:47 pm

There is a fellow by the name of Dr. Carl Whitcomb who spent the bulk of his career studying the part of the plant we don’t often see. Much of Dr. Whitcomb’s research set the horticulture industry on its ear. One of the simpler yet more enlightening ideas that came from this lifetime study was the fact that roots grow during winter. This was proven correct in subsequent studies and so it came to pass that Fall and Winter became the optimum time to plant trees, shrubs, and most long lived perennials.
While it is true that warm season annuals, vegetables, and warm season grasses by their very nature must be capable of vigorous root growth during Spring and Summer, the plants that have longer life spans apparently have a different agenda. You may even recall old timers who expressed this as, “The sap rises and the sap falls” as trees green up in Spring and go dormant in Fall. Even though sap is produced in the upper portion of the tree and does not “rise and fall” (there is no sap in root systems), it is clear that our forefathers at least had a concept that seems to agree with modern science.
Roots store energy. This is highly apparent in the many bulbs, tubers, and rhizomes that can be dug up and dried but still come to life after transplanting. Plant a potato or an onion set in late winter. Dig one up periodically and check on it. Before the soil has warmed enough for the top to emerge, roots will have begun to grow.roots1 Obviously these plants have to be drawing stored nutrients from the bulb or tuber. The same holds true of all plants that have a large or extensive root system.
When you think of underground temperatures, root growth during the cool season makes perfect sense. No matter where you live, once you get below the frost line, underground temperatures remain constant year round. This is the main principle behind geothermal heating and cooling, your local building code for underground utilities, not to mention the old fashioned “root cellar.” It comes as no surprise that many early Texans chose to live in dugouts. They were naturally warmer in Winter and cooler in Summer.
As plants shut down for the Winter we eventually have days when the temperature above ground is much colder than the temperature below ground. This is a time when plants will concentrate on root expansion. The top is cold while the roots are down in the well insulated warmth under ground. The top of the plant has stopped growing therefore the stored energy can be used by the roots. Seems logical doesn’t it?
Another period when we see a marked increase in root activity is in late Winter and early Spring as the topsoil begins to warm. We have known for a very long time that trunk expansion occurs during this same time. Tree trunks and limbs are above ground and easily measured. Root growth and trunk expansion will occur generally before bud break.
During the growing season our trees, shrubs, and flowering perennials spend most of their energy making new leaves, branches, flowers, and finally seeds. Here we get to a point where the air temperature is typically warmer than the soil. At this point our roots are busy supplying water and dissolved minerals to the top. The roots do remain active during the warm season but the bulk of the energy goes to the top. During our typical long hot summer there is often a second dormant season.
Dr. Whitcomb along with other innovators such as the late Benny Simpson actually proved you could dig up transplant trees in the heat of summer as well as the dead of winter. Apparently active top growth does shut down during this second dormant season. The problem with moving trees in summer has more to do with the physical characteristics of the soil itself.
roots2 If you have ever put in a fence or dug a hole for any reason in summer you likely found the dry soil to be just slightly harder than your average brick. You learn real quick to water those post holes and come back the next morning to dig. Digging trees in August is just plain hard work. Conversely, those same rock hard soils dig nicely after the Fall rains soak in. Evaporation rates are low in the cool season so what moisture does fall tends to soak in and stay there. Now I ask you, if you were a root, when would you want to grow? In the dry hard soil of summer? I think not.
So the season for maximum root growth begins in Fall, lasts through Winter in our warmer southern states, and ends with a good spurt of growth as the soil warms in Spring. Here is an easy way to check this for yourself if you would like. Buy a small tree or shrub in April when most folks think is the best planting season. Dig this plant back up in mid Summer. You will observe that the roots will have grown very little. Generally the roots will still retain the shape of the container it was in when you bought it. Now, apologize to your specimen for the inconvenience and put it back in the soil. Inspect it once again as the next April rolls around. You may have set the plant back a good deal in the name of science but you should see a remarkable difference.
So what we have here is a general misconception that late Winter and early Spring are the ideal times to plant. On the other hand, we continue to hear from Dr. Whitcomb and indeed, from nearly every well informed member of the nursery and landscaping industry that Fall is the time to get busy. At least for those of us who live in the south and especially in the western two thirds of Texas where bone dry summers with seriously hot temperatures are considered normal.
Remember that the first thing that emerges from any seed is the root. The top comes later. If you keep this in mind and apply it to all your gardening endeavors your success rate will definitely improve. That beautiful potted plant you bought certainly had healthy foliage. That healthy foliage is a reflection of a vigorous root system. Cut the top off and new growth will soon emerge. Cut the roots off and what you have is a dead plant. Think about the roots and you will automatically become interested in improving the soil. Why did your plant turn brown “all of a sudden?” Could it be that the roots may have dried out? Quite likely………………….
The season of the root begins in Fall. It has always been that way and as long as we have four seasons that will not change. Because we humans live above ground and rely heavily on our eyes as the most useful of our sensory input we tend to draw the wrong conclusion. The most important part of any plant is below ground. The old phrase “Out of sight, out of mind” fits perfectly. If we could only see underground then our habits would surely change. Planting in Fall would not be hard to sell.
Instead, yours truly along with every other gardening columnist in the south will continue to write these articles each Fall. Next Fall we will likely write another. Next Spring the Mega marts will saturate the local media and clean up with their ad campaigns. Next Summer most those Spring beauties will suffer. Many will die, especially during drought years. Novices and newcomers will write it off and decide they just don’t have what it takes to be good at gardening.
Meanwhile you can try these experiments or one of your own and pass it along. Plant a tree this Fall and another tree of the same type next Spring. See which looks best during the stressful time of Summer. By all means, draw your own conclusions. Perhaps the day will come when the Mega marts will do landscaping ads in the Fall???……………..Don’t hold your breath.

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