Proper root care reaps big rewards: Dan Gill's garden advice

(Illustration by Kenneth Harrison)
on August 30, 2013 at 11:50 AM, updated August 30, 2013 at 12:01 PM
Plants don't just drink when they're thirsty. They must absorb water from soil constantly.

A plant's root system has a profound effect on its overall health. Look at the roots of a sick, struggling plant, and you'll generally see a sick, struggling root system. While plants can tolerate a fair amount of damage to their upper parts, they're not nearly as forgiving of damage to their roots.

Think about it. A leaf spot disease can severely damage a plant's foliage. The disease may cause virtually every leaf to fall off. Yet if the roots and stems remain healthy, the plant can grow new leaves and recover.

Lately we're seeing examples of this in crape myrtles with Cercospora leaf spot. Even with major leaf loss, crape myrtles are able to fully recover.

I'm sure most of you have seen tropical plants that were frozen to the ground by a hard freeze and then rebounded. Since the roots were protected in the soil and not damaged, the plant could rapidly regrow.

In a similar way, you can cut some trees down to the ground, and the base of the trunk will sprout.

Now, take a plant and cut off all of its roots. What chances would you give it? None, of course. It will die.

The work of roots

There are three primary functions for roots: food storage, absorption of water and minerals, and anchoring.

When we eat carrots, turnips, radishes and sweet potatoes, we take advantage of plants that store food in their roots. Plants often store food in their roots to get them through a dormant period.

The ability of roots to absorb water and minerals is key to plant health. Plants don't just drink when they're thirsty. They must absorb water from soil constantly. It's 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 work, transplanting or filling is often life threatening to plants.

Roots also serve to anchor plants in place. This is an especially critical role when it comes to our shade trees and hurricane winds. A strong root system is key to preventing a tree from going over on your house.

Damaging a tree's root system -- most of which is in the upper 18 inches or less of the soil -- by digging, trenching or the use of heavy equipment can not only effects the health of the tree, but, if it survives, can make the tree less able to withstand high winds.

Gardeners rarely realize how many gardening techniques are done for well being of roots -- from tilling the soil and the addition of organic matter during bed preparation, to potting soil selection, the use of drainage holes in pots, the timing of planting or transplanting, and the benefit of mulches.

Here are some useful gardening terms and their relationship to roots.

Establishment: Root growth into the surrounding soil after a plant is newly planted. This is critical to the long-term survival of a landscape plant. Once a strong root system has grown into the surrounding soil, the plant is considered established. During the establishment period, plants require extra care, particularly with watering. A limited root system cannot obtain water as efficiently. 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 where water does not stand for extended periods of time or remain saturated long 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 situations, the vast majority will not tolerate soils that stay too wet for too long. We plant in well-drained beds specifically to make the roots happy.

Filling: Applying soil over an area to raise the grade. Filling over tree roots too deeply can deprive them of oxygen and lead to root death and the loss of a tree.

Bed preparation: Work done to improve soil for plant growth. Tilling or turning of the soil down about 8 inches is a common aspect of bed prep. Loosening and breaking up soil makes it easier for roots to penetrate 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 an environment more favorable to root health. When planting trees, dig holes two to three times as wide as the rootball. That will encourage the 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 the summer and warmer in the winter. Mulches also help prevent evaporation from the soil surface, conserving moisture.

When it comes to the importance of root health, I'm just getting started. Whether or not a plant survives being transplanted depends largely on digging it up with enough of its roots.

As for container plants, they only can live in a pot for a limited time before the roots run out of space and become pot bound. The plant will need to be shifted into a larger container or planted in the ground to remain healthy.

I once saw a refrigerator magnet that said, "When Momma ain't happy, ain't nobody happy." Substitute "root" for "Momma" and you will have the essential message of this column.

Always remember that 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 their needs.