Grass has the amazing attribute of being able to produce tons of livestock feed then to be mowed or grazed and grow greater quantities and better quality again and again. Some trees can be pruned or trimmed and continue to grow and produce fruit but only after considerable time for rejuvenation. Ornamental flowers are clipped and expected to grow back next spring or summer, but grass can be grazed or harvested repeatedly in a growing season. Grasses are tremendous producers. But not all grasses react to defoliation in the same way, so grasses must be studied to best utilize this outstanding feature.

A grass seed contains nutrients to help the plant begin to grow. In spring, soil temperature, moisture, planting depth and seed vigor contribute to a seedling (cotyledon) emerging from the seed. All grasses are hypogeal, which means the first leaf remains below the surface of the soil. Also from the seed, a primary root called the radicle emerges. Additional roots soon develop from the seed and are called seminal roots. These roots are crucial for the absorption of water and nutrients but are short-lived. After the root growth is underway, the shoot (epicotyl) emerges and grows towards the surface. At first, since the development is underground (hypogeal) and since there is so little leaf material available to manufacture sunlight energy for growth, the plant uses stored carbohydrate reserves within the seed. But quickly a tube containing leaves (coleoptile) elongates toward the soil surface and emerges. It then stops growing, but leaves within unfurl and begin utilizing the sunlight. Since the primary root and seminal roots are short-lived, new roots (adventitious roots) develop if soil moisture is sufficient. With appropriate temperatures, leaf production then proceeds rapidly. Within a week, buds at the bottom of sheaths of lower leaves develop into new stems called tillers. Usually by the time three leaves appear, one or two tillers are visible. For the first month or so, the plant is busy producing leaves and tillers. This will continue until climatic conditions trigger the plant to focus on reproduction. Then the plant will elongate and send up a flag leaf and then a peduncle which is a stem that will support a reproductive inflorescence. The goal of forage production is to utilize grass growth before the reproductive stage when stems thicken and quality and palatability decrease. Managers must learn to use leaf material wisely and, if possible, postpone the reproductive stage.

It is interesting to learn that various grass species have specific patterns of leaf/tiller growth patterns. For example: perennial ryegrass will produce three leaves and then a tiller. And leaf formation will directly reflect a specific number of growing days when temperatures are conducive for growth. It is wise to learn the specific growth pattern of the grass species you produce.

Growth Sequence

When a grass plant has been defoliated (grazed or mowed) and some leaf material remains, the plant can continue growth because leaves will utilize sunshine and so photosynthesis continues. If defoliation severely reduces the leaf material, stored carbohydrates must be used for new growth because there is not enough leaf surface to support photosynthesis. The plant stops root growth and other functions to focus on replacing leaf tissue. Managers need to encourage leaf growth without using carbohydrate reserves and stopping root growth. This requires managing defoliation so that enough leaf surface remains to continue the photosynthesis process.

Another way to address this same growth process is to look at the apical meristem. Grass plants have a growing point called the apical meristem located in a bulge in the stem. It initiates new leaf growth, supports new buds and develops cells of the nodes. All of these functions actually determine the growth rate of a plant. This meristem remains close to the soil surface for quite a while. When climatic conditions are right and the plant is of good size, the meristem develops (differentiates) into a flower (inflorescence). Then it is pushed to the top of the plant, produces seed and dies. The root system of a plant also dies when the inflorescence dies. But while the meristem remains vegetative (not differentiated) and intact, the plant can be very productive in leaf developement even after grazing or mowing. If the meristem is grazed or mowed, however, new growth will cease. New growth can only continue from other sources like "daughter plants" called tillers. Tillering can take two forms, a vertical growth pattern which results in grass growing in bunches or horizontal growth resulting in grasses that form a sod or carpet. Bunch grasses, like orchardgrass, big bluestem, and wheatgrasses, sometimes only produce a few tillers. But sod-forming grasses, like Kentucky bluegrass, bermudagrass, and some bromegrasses, may send many tillers out and away from the plant by either underground (rhizome) or above ground (stolon) branches. Bunchgrasses allow for more competition from other plants by leaving open soil, so legumes are often planted with them. Sod-forming grasses usually have abundant terminal meristems and lots of leaf area close to the soil surface which results in better stability when the grass is closely or frequently grazed or mowed. They also work better for areas of heavy traffic.

As the growing season progresses, grass can be mowed or grazed and will continue to regrow as long as the meristem remains intact. The meristems may be the growing point or the area where the leaf blade wraps around the stem called the intercalary meristem. Growth is high-quality, leafy forage resulting in high animal performance. When a plant is reproductive (after differentiation of the growing point meristem), the palatability and digestibility of a grass plant is lower than leafy vegetative grass plants. Unless the grower is interested in seed production, forage plants are better feed when in the vegetative stage and repeated defoliation actually helps maintain that.

Once defoliated, grass will grow back from several ways but there are variations in how that is done. Grasses grow back because the base of the leaf blade, if not removed, expands and grows. Or regrowth can come from new leaves, tillers and buds. Some plants also have corms, which are carbohydrate reserves that look like bulbs near the surface of the soil.

Some grasses grow back in the same way they first grew. They are sometimes called jointed grasses but that terminology is confusing because all grasses have jointed stems. Basically "jointed grasses" grow back with the same leaf/tiller pattern and elongation of the stem during the reproductive phase as was seen in initial, undisturbed growth. These grasses must be managed carefully because the growing point can be elevated and become vulnerable to defoliation. These grasses include timothy and bromegrasses. However, some grasses regrow without the repeating the elongation of the stem for reproduction. These "nonjointed grasses" are more tolerant of continued grazing because the growing point is not continually elevated and therefore remains intact for future growth. Pastures with a mixture of grasses can be difficult to manage when jointed grasses are growing with nonjointed grasses.

Another factor involved in regrowth is that all grasses produce some tillers that do not flower. They are sterile tillers. Some grasses have many sterile tillers while others have a low percentage of sterile tillers. The sterile, nonflowering tillers maintain a low growing point so are less vulnerable to defoliation. The growing point may affected by long periods of dry conditions and long rests may cause the leaf blade base (intercalary meristems) to extend and be removed by grazing or clipping. But, generally, grasses with many sterile tillers will respond well to intensive grazing.

At the end of the growing season, a manager of grasses and legumes must consider when to mow or graze for the last time before winter arrives. The grass plant needs enough reserved carbohydrates to last the winter and begin new growth in the spring. A severe defoliation late in the season will remove the site of late photosynthesis and the plant will utilize reserves for root growth and plant functions and then will not have enough reserves for winter use and spring regrowth.

Forage managers can produce much more forage and have forage stands persist much longer when they understand how grasses grow and regrow. Though most grasses grow similarly in initial growth and when left undisturbed, grass species vary in regrowth mechanisms. This is crucial since the greatest benefit of forage is its ability to regrow many times in a growing season.