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You should know how grass grows

It’s important to understand how grasses grow so you can better manage them. In this column, I will talk only about cool-season grasses such as ryegrass, tall fescue, orchardgrass, smooth bromegrass, timothy and reed canarygrass, and not warm-season grasses — bermudagrass, bahiagrass and switchgrass, for example.

New seedings

The ryegrasses and festoliums will come up first and dominate early in the season. In July you should expect to see some of the longer-term perennial grasses growing and contributing to the stand. We usually only think of soil pH with regard to legumes, but it is important to recognize that, while all grasses will survive at low soil pH, some will yield significantly more if the soil pH is above 6.0.

Second, it is important to recognize that most cool-season grasses do not head out in the seeding year. They require vernalization, exposure to a period of cold, to flower and produce seeds. Therefore, grasses should be cut or grazed by height in the seeding year.

The general recommendation is to cut when the associated legume is flowering, or to graze or cut when the grass reaches 12 to 15 inches height. This is especially crucial if seeding a cover crop (such as oats or ryegrass) with a longer-lived species so the cover crop does not shade out the slower-establishing grass (e.g. tall fescue, orchardgrass, etc). The main consideration with grazing is to ensure the plant has a sufficient root system so the grazing animals do not pull the plants out of the ground.

Regrowth in stands

Grasses have three types of growing points:

Apical meristem is the growing point in the crown at the tip of the stem that produces a head. It stays at or below ground level early, producing a cluster of leaves; then the stem extends, pushing up the head. If the head is grazed off or clipped, this meristem quits growing.

Intercalary meristem is the growing point at the base of the leaf and the leaf sheath. All cell production and growth for the leaves and sheaths occur here, not anywhere else along the length. This is why grazed or mowed plants show leaves continuing to grow.

Axillary buds at plant nodes produce regrowth triggered by grass maturity or removal of growing points in timothy and smooth bromegrass. If the head of these species is removed, new shoots may develop from stem nodes. The effect is triggered by environment and genetics in orchardgrass, tall fescue and ryegrass.

Because most cool-season grasses require vernalization for heading (except timothy and ryegrass), they only produce seed heads on first growth in the spring and only leaves on regrowth. Two exceptions are smooth bromegrass and reed canarygrass, which produce stems (but no seed heads) during regrowth. Orchardgrass, ryegrass and tall fescue store energy in basal stems; therefore, cut at 4 inches for rapid regrowth.

A basic rule of grass growth is that growth takes priority over storage for carbohydrates. If grazing animals remove most of the available leaf area every few days, the plant allocates nearly all growth energy to new leaf growth, the root system diminishes, and less energy is stored. Frequent leaf removal without adequate time for the plant to restore its vigor is the physiological basis of overgrazing. Overgrazed pastures produce far below their potential, maintaining only a low stand density and poor vigor. Most grasses store some energy for regrowth in stem bases, so grasses need to be taller (3 to 4 inches) than legumes.

Some grasses are slow to recover because they only produce buds for regrowth after they have been cut or grazed (such as bromegrass and timothy). Other species produce buds sooner in the growth cycle and therefore recover faster for haying or grazing (such as orchardgrass and tall fescue).

Some grasses have basal leaves that remain after mowing or grazing, which help the grass grow back faster (such as bluegrass and ryegrass). Orchardgrass, reed canarygrass, tall fescue and smooth bromegrass will have some leaf area remaining if cut or grazed at 4 inches or higher, but not if cut shorter.

Adequate N

Last, it is important to note that grasses need nitrogen fertilization continuously throughout the season. Grass takes up available N on a growth cycle and leaves little for the next. Nitrogen deficiency is most visible in pastures where the tall green ring around a manure pile indicates how tall the rest of the pasture could be if it had received the same N.

We generally recommend about 50 pounds of N per acre applied three times during the year (early spring, mid-June and early August). A single application of 150 pounds will provide too much N early and will result in N deficiency and reduced growth in the fall.

Undersander is a University of Wisconsin-Madison Extension and research forage agronomist.

This article published in the August, 2010 edition of WISCONSIN AGRICULTURIST.

All rights reserved. Copyright Farm Progress Cos. 2010.