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rrigated pastures are complex biological systems involving soil, sun, water, plants and animals that provide forage for your animals. Think of yourself as a “grass farmer” first and foremost. The forage is the crop; the grazing animals are the crop harvesters.

How Grass Grows

To maintain healthy grass pastures and livestock, a general rule of thumb is to manage grass height so that it ranges between three to eight inches high. These management heights vary by grass species. Graze the pasture when eight inches tall. Rotate the animals to the next pasture when grass is three inches tall.

The Deschutes SWCD has free pasture sticks available to help identify grass height.

Grass plants must have adequate leaf area (solar panels) to photosynthesize optimally Photosynthesis is the process of converting the sun’s energy into plant biomass. Plants with few leaves have fewer roots, making it more difficult to absorb necessary nutrients and water from the soil. Grass roots are actively growing in the spring and the fall; the roots are “shedding” in the summer and winter. Grass plants store most of their food reserves in the crown area (bottom two to four inches) of the plant. These stored food reserves consist of sugars and nonstructural carbohydrates. Grasses utilize food reserves for regrowth and to survive periods of dormancy. (Legumes store most of their food reserves in the root.)


Deschutes County Rural Living Handbook

Growth rates grasses vary seasonally. In general, our Central Oregon cool-season grasses grow rapidly in the spring (until about June 21), then go through a “summer slump” of reduced growth, then grow more rapidly in late summer to early fall, and then go dormant until spring. Managing for proper fall stubble height is important. Regrowth in the fall contributes to next year’s first grazing or first cutting of hay. The more green leaves, the quicker the plants will regrow to provide forage for animals. If grass is grazed short when the roots are actively growing (spring and fall), then the summer slump and winter dormancy will negatively affect grass growth and will negatively affect grass growth even more the following year. Fall is the worst time to graze grass very short. Legumes, like alfalfa and clover, grow better than coolseason grasses in hot weather. Clover can take over an overgrazed pasture in the summer because of its heat tolerance and comparative leaf-area advantage.


Pasture plants need nutrients, such as nitrogen, phosphorus, potassium and sulfur, as well as other nutrients to grow properly. Grazing can either concentrate or remove soil nutrients within the pasture; therefore, a fertility plan should be developed. Conduct a soil fertility test every three to four years (ideally in the fall) to determine what kind and how much fertilizer is needed and then monitor over time.


Grass plants can efficiently use about 50% of the available water from the soil. Grasses will extract water to a depth of two to three feet, depending on grass species and soil depth. Once half of the available water has been used, it is time to irrigate. Daily plant water requirements vary based on factors such as air temperature, solar radiation, day length, wind and

Deschutes rlh 2010