Pine straw is an excellent mulch that helps keep plant roots cooler in summer and warmer in winter. (Photo by Mark Claesgens) For Release On Or After 08/15/14
By Dan Gill
LSU AgCenter Horticulturist
I once saw a refrigerator magnet that said, “When Momma ain’t happy, ain’t nobody happy.” Substitute “roots” for “Momma,” and you will have an essential message when it comes to plants. Always remember that the roots are the foundation of a healthy plant. And whether you realize it or not, much of what you do as a gardener is guided by the needs of the roots.
The condition of a plant’s root system has a profound effect on its overall health. While plants can tolerate a fair amount of damage to their upper parts, they are not nearly so forgiving of damage to their roots.
Think about it. A leaf spot disease can attack and severely damage the foliage. The disease may cause virtually every leaf to fall from the plant. Yet, if the roots and stems remain healthy, the plant can grow new leaves and recover.
We are currently seeing an example of this in crape myrtles with Cercospora leaf spot. Even with major leaf loss, crape myrtles are able to fully recover, and their lives are not in danger. Indeed, cut a crape myrtle down to the ground, and the base of the trunk will sprout and grow vigorously.
This shows the amazing ability of plants to recover even from extreme damage to their upper parts, as long as the roots are in good shape.
Now, take a plant and cut off all of its roots. There is no way it can recover. It’s done for and will die. Plants are much less forgiving of damage to their roots than they are any other of their organs.
This is due to how roots function and the role they play in the life of a plant. Two of the primary root functions are absorbing water and minerals from the soil and anchoring the plant.
The role roots play in absorbing the water and minerals plants need is why plants are so dramatically affected when their roots are injured. Plants don’t just drink when they are thirsty like we do. They must continuously absorb water from the soil. Constantly absorbing water is important to their ability to move fluids up through their circulatory system without a pump (heart). Damage to the roots from root rot fungi, construction, filling or transplanting reduces a plant’s ability to absorb the water it needs. Root damage is often life-threatening and can have an immediate and profound effect on the health of a plant.
Roots also anchor plants in place. This is an especially critical role when it comes to our shade trees and the high winds of hurricanes and strong storms. Never forget that the only thing that keeps a big tree from falling on your house in high winds is a strong root system.
As a result, we need to carefully protect the roots of our trees from damage. Damaging a tree’s root system, most of which is in the upper 18 inches or less of the soil, by digging, trenching, using heavy equipment, etc., not only affects the health and life of the tree but can make it less able to withstand high winds.
Gardeners rarely realize how many gardening techniques are done with the roots in mind and for their wellbeing – including tilling the soil and adding of organic matter during bed preparation, the timing of planting or transplanting and using mulches. Here are some gardening terms that are useful to know and how they relate to plant roots.
Establishment: The growth of roots by a newly planted plant into the surrounding soil.
This is critical to the long-term survival of a plant in the landscape or garden. Once a strong root system has grown into the surrounding soil, the plant is considered established. During the establishment period, a plant requires extra attention and care, particularly when it comes to watering. The limited root system cannot obtain water as efficiently or from as large a volume of soil. Flowering bedding plants and vegetable transplants generally take about two to four weeks to establish. Shrubs take about a year to properly establish. Trees are generally established after about two years.
Well-drained: A location or bed where water does not stand for extended periods of time, or stay saturated for long periods after rains.
Roots need oxygen to be healthy, and that oxygen is obtained from air spaces in the soil. Although some plants are adapted to wet or boggy soils, the vast majority of the plants we grow and cultivate will not tolerate soils that stay too wet too long. Planting in well-drained beds is done specifically to make the roots happy.
Filling: Applying soil over an area to raise the grade.
Filling over tree roots too deeply deprives them of oxygen and can lead to root death and the loss of a tree.
Bed preparation: What is done to the soil in an area to change or improve it in a way to encourage the plants we plant there to grow their best.
A common aspect to bed preparation is tilling or turning the soil down about 8 inches. Breaking up the soil makes it easier for plant roots to penetrate the soil and grow. It speeds establishment and encourages a strong root system. It also incorporates oxygen into the soil. Organic matter commonly added during bed preparation helps to create a soil environment more favorable to root growth and health. When planting trees, holes are dug two to three times as wide as the rootball. Loosening the soil out from the rootball encourages the tree’s roots to grow out and establish the tree.
Organic mulch: Materials such as pine straw, leaves, wood or bark chips applied to the soil surface.
Although we often focus on the attractive appearance and weed-control functions of mulches, roots also benefit. Mulches moderate soil temperature – keeping the roots cooler in summer and warmer in winter. Mulches also help reduce wide swings in moisture content by preventing evaporation from the soil surface and conserving moisture.
Rick Bogren