Reseeding Horse Pastures in the Fall

Q. I’m reseeding our pasture this fall, and in looking for seed I’ve found mixes that are warm-season grass mixes and others that are cool-season mixes. What are warm- and cool-season grasses, and which one should I plant?

A. The difference between cool- and warm-season grasses lies in how they conduct photosynthesis. Both types use light energy from the sun and, using water and carbon dioxide, make sugars as an energy source for the plant.

Carbon dioxide + water + sun light energy → sugars + water+ oxygen

Because of the different pathways grasses use to capture carbon dioxide during photosynthesis, cool-season grasses are sometimes referred to as C3 plants and warm-season grasses as C4 plants. These pathways are associated with different growth requirements.

Warm-Season Grasses

For instance, C4 plants are more efficient at capturing carbon dioxide and nitrogen from the ground and air than C3 plants. They also tend to have lower crude protein contents, need less water, and prefer warmer climates. In fact, warm-season grasses don’t begin to grow until the soil temperature is 60-65 degrees Fahrenheit, and they grow best when the air temperature is between 90 and 95 degrees. Examples of warm-season grasses include Bermuda grass, blue gamma grass, and buffalo grass.

Cold-Season Grasses

As the name suggests, cool-season grasses do best in cooler weather conditions. Growth begins when temperatures are as low as 40 to 45 degrees, and they grow best in between 65 and 75 degrees. As temperatures rise, these grasses become less efficient and lose more captured energy (anywhere from 15 to 40%) to photorespiration (a wasteful process by which plants take up oxygen and give out carbon dioxide).

Grasses for Horse Pasture

Many grasses horses consume in pastures or as hay are cool-season species. Cool-season grasses can be annual, such as rye and oats, or perennial, such as timothy, orchard, fescue, and perennial rye. Cool-season species also tend to have higher protein levels than warm-season grasses. Alfalfa is a cool-season legume and can have very high crude-protein levels.

Generally, cool-season grasses have the most active growth in spring and fall due to cooler days and nights, shorter days (less energy lost via photorespiration), and higher soil moisture. They go somewhat dormant in the summer, especially if seedheads develop. Conversely, warm-season grasses are most active in the hotter summer months and are dormant from fall through spring.

As to which grass you should plant in your horse pasture, the decision will come down to factors such as the climate where you live, seasonal high and low temperatures, day length, etc. If you live in a region where much of the summer remains at temperatures at or above 90 degrees, then it would be smart to seed at least some of your pasture with a warm-season grass. The warm season grass would be coming in to its own as the cool-season grasses become dormant in the hotter weather, and visa versa in the spring and fall.

Pasture Grass Planting Tips

Fall isn’t the time to plant Bermuda seed, because temperatures are dropping. Warm-season pasture grasses like Bermuda need to be sewn in spring and/or early summer. Even cool-season species do better when seeded in spring but can be seeded in early fall in time for fall growth. Exact timing of seeding will depend on your location, elevation, exposure, prevailing moisture, and weather.

Don’t let horses graze seeded pastures for a considerable time, because they graze very close to the root. Depending on the species, allow plants to reach at least 8 inches (for perennial rye) to as high as 20 inches (for alfalfa) before grazing or mowing. Allowing your horses access before this risks damaging young plants that don’t yet have an established root base.

With careful consideration of your climate and needs, you can determine the best grass species to plant. If in doubt, contact your local university extension office, because staff and faculty there will have good working knowledge of your area, what grows best, when to plant, and how to manage for optimal results.