Spring Technical Guide: Managing Plant Health Through Better Root Growth

That’s the root of all evil.”

“This is about as much fun as a root canal.”

How many times have you heard similar analogies about “bad” roots? Now, how about a good title, such as, “Up with Roots?” No, that would never work — it’s not agronomically feasible. How about “Roots —Out of Sight and Out of Mind?”

Understanding roots means we must go back to the basics — what, how and why roots benefit plants. One of the more obvious benefits is that roots are essential for plant growth. They provide anchoring for the plants and permit the absorption of nutrients and water.

Root systems generally fall into two classifications: fibrous or tap root. Grasses are classified as having fibrous root systems characterized by a fairly shallow, multibranching arrangement.

Many other plants have a tap root system characterized by a primary root, which remains the largest root of the plant and develops downward with other roots branching from it. Tap root systems are present in large and small plants. The dandelion is an excellent example of a small tap root system.

By knowing about the plant’s root system, a lawn or landscape contractor can select the best practices to allow for maximum plant growth. Knowing whether the root system will require depth or lots of lateral space, as well as how quickly it will develop, will help you prepare a growing site or select the proper container for that plant.

ENVIRONMENTAL EFFECTS. Various environmental factors affect plant root growth, as well as the direction and extent of root growth. Some of these factors include temperature, light, gravity, salt concentrations, condition or texture of soil or planting medium, oxygen supply and nutrient availability. All of these factors combine to facilitate root growth and, as such, dictate the amount and direction of root growth.

For example, the effect of light on plants is called “phototropism.” The light availability causes an imbalance of hormones in some parts of the plant which may cause the plant to grow toward the light (positive phototropism). Some roots will turn away from light (negative phototropism). Gravity causes an imbalance of hormones in roots which causes them to grow downward (positive geotropism). Growth toward moisture is called “positive hydrotropism.” Growth toward favorable temperatures is called “positive thermotropism.” One landscape manager even claimed that willow trees exhibit special effects he called “septic tanktropism.”

At any rate, plant roots do not seek out favorable growing conditions, but they do grow in the direction of the most favorable conditions that they encounter.

GROWTH PATTERNS. Roots grow by cell division and elongation. Basically, new cells are formed behind a tough battering ram called a “root cap.” Once formed, these new cells begin to elongate, which accounts for the movement of roots through the soil.

Directly behind the elongation zone is the area where root hair and vascular tissues are formed. This area is primarily responsible for absorbing nutrients and water.

Primary, or seminal roots, develop directly from the seed and are generally short-lived, lasting only about six to eight weeks before being replaced by the adventitious roots. These roots form from underground stems, older roots or aerial plant parts. Adventitious roots also develop from nodes of rhizomes and stolons of perennial grasses. On more developed, older turf, most of the new roots develop on the outer edges of the original shoots and from nodes of the newest tillers or creeping stems.

Turfgrasses can develop root systems which can reach a depth of 5 to 7 feet for warm-season grasses like Bermudagrass, St. Augustine or bahiagrass. By contrast, roots of cool-season grasses like bentgrass or Kentucky bluegrass seldom reach below 1½ to 2 feet when turf is maintained at a 2-inch cutting height. The root system of a healthy turf plant is usually thick , multibranching and forms a heavy, fibrous net. Newly formed roots appear thick and white, while older roots are thinner and darker in color.

Root longevity depends on a number of factors. Primary roots usually do not live past the first year following seeding or planting. Adventitious roots may last as long as the plants they support. In cases of unfavorable growing or soil conditions, however, these roots may die while the plant shoot will survive. This case is particularly likely for cool-season turfgrasses during the midsummer heat stress periods.

Most cool-season turfgrass root growth occurs in the spring and, to some extent, during fall weather. Warm-season turfgrass root growth will occur mainly in the summer months.

Root replacement will vary with the type of turfgrass. Kentucky bluegrass will retain most of its roots for more than one season and is referred to as a “perennial rooting grass.” Other grasses like bentgrass, perennial ryegrasses and rough bluegrass replace most of their roots yearly and are considered annual rooting grasses.

New research is being conducted to see if altering the turfgrass plant’s growth habits can aid in root system retention and also increase root growth.

STUNTING GROWTH. What can go wrong for roots? What evil lurks in the soil that can cause their demise? Unfortunately, there are numerous factors that inhibit root growth and longevity. They include pH, salt concentrations, moisture variations (either a lack or a surplus), lack of oxygen, chemical actions, soil compaction and high soil temperatures. In addition, some cultural practices inhibit root growth, including mowing at less-than-recommended heights or with too much frequency, excessive amounts of nitrogen fertilizer and a deficiency of potassium fertilizer.

All of these root-inhibiting conditions can be managed.

BREATHE DEEP. One of the cardinal rules for all living cells is that they must have access to oxygen. Amounts necessary for active growth will vary according to the species, but cutting off the supply through flooding or soil compaction can either reduce or completely eliminate root growth and survival.

“Compaction is the foremost turf problem,” stated researcher J.H. Madison, “by causing an overall decline in growth, quality and vigor.”

One of the major problems with compaction is that it is seldom recognized as the cause of root decline and, therefore, overall turf demise. Soil compaction’s most conspicuous rooting response is altered root distribution. Most times, a decrease in deep rooting will occur, while a substantial increase in surface or lateral rooting is a strong clue that compaction is the culprit.

During summer months, compaction has been shown to increase root dieback, although it could be attributed to increased soil temperatures and less favorable soil oxygen levels. Both of these problems are directly related to soil compaction and both have been proven to hasten root maturity.

Several studies have borne out the related problems of compaction, low oxygen soil content and reduced water uptake. In one study, compacted Kentucky bluegrass was shown to suffer both root and shoot growth reduction, often exhibiting lack of moisture symptoms even after frequent irrigation. Exercise care on frequently irrigated, high-use recreational turf areas to prevent undue compaction which can result in decreased plant vigor and growth.

The author is an industry consultant with Key Solutions, a division of Iris Sales & Solutions Inc., Rocky River, Ohio.