Walk your pasture to find out what's changing

By Ellen Nelson
Larimer County Weed District

The summer growing season is winding down, and it is a good time to assess the condition of your pasture and plan your fall weed control.

Walk your pasture and note the height and vigor of your grasses. After above-average rainfall this spring and early summer, your grasses may be more vigorous and healthy than in years past when we were experiencing drought.

As you walk, ask yourself some questions about what you are seeing. Did grasses produce a seed head and set seed, adding to the seed bank of beneficial seeds in your soil? Are there new or unidentified plants in your pasture? Are they noxious weeds that you will want to control before they increase? Are they natives or useful forbs that will add diversity to your pasture? Are there plants that may be toxic to livestock? Are you seeing increased patches of bare ground?

As part of your pasture assessment, you may want to begin the practice of taking a picture of your pasture from the same location at the same time every year. These pictures will provide an accurate record of how your management practices affect the land over time. If you are seeing increased bare ground or large patches of undesirable plants, you may need to assess your grazing practices. Your goal should be to harvest 30 to 50 percent of the forages that grow in your pasture every year.

If your animals remove too much of any individual plant, over time these plants will become debilitated, less vigorous and unable to compete with undesirable plants. Your pasture will gradually become sparser, will produce less forage, and will be easily invaded by weeds. More annual grasses and weeds taking the place of desirable perennial grasses indicate pasture decline.

How do you determine when to graze and how long to graze? You will want to develop an awareness of the condition of the plants in your pasture. You are already adept at observing your horse and knowing its condition and general well-being. You can develop the same sort of empathy with plants.

It is important to understand how grass grows. The plant's leaves are solar collectors; they convert sunlight to stored energy. When an animal removes these leaves by grazing, the plant uses stored energy from its roots to replace the leaves. New leaves then go to work capturing sunlight, and producing energy to replenish the energy from the roots and to grow more leaves.

It is critical to replace energy removed from the roots, just as it is important for you to replace money in your bank account after you withdraw to meet your monthly budget needs. If you continually withdraw, but never replace, your financial state will rapidly become unhealthy. The same is true for the grass plants in your pasture. After being grazed, the plant requires a rest or recovery period to regrow leaves and to replace energy stores used to grow the new leaves.

For maximum plant vigor, the plant should not be grazed again until it has had adequate time and opportunity to regrow what was grazed. This regrowth can occur in as little as two to three weeks when there is adequate moisture, but during dry periods, it could take as long as three to four months. In some very dry parts of the country, a pasture will need to be rested an entire year before it can be grazed again.

Understanding what is required for plants to grow new leaves will guide your judgment about when and how long to graze. Spring growth may require more energy than can be provided by initial photosynthesis, so it is prudent to wait several weeks after grass plants have first greened up before turning horses out to graze. A good rule is to wait until the plants are 8 to 16 inches tall, and have at least four to six leaves.

As a guideline for how long to graze, use the second-bite rule: Remove horses from pasture before they have the opportunity to take a second bite of the same plant, and allow a grazed plant adequate time to regrow before it is bitten a second time.

Most small-acreage pastures in our area do not produce enough forage to support a horse. An acre of a typical dryland pasture in northern Larimer County will, on average, produce enough forage in one year to feed one horse for about one week. On small acreages, it's wise to purchase most of your forage and use your pasture as a turnout for an hour or so per day. Feed your horses before turning them out, and monitor your pasture to see if this change in grazing routine improves the health of your pasture. Another approach is to divide your pasture into several smaller pastures and rotate your stock through these smaller pastures, allowing the ones not in use to recover.

You may decide that it is simpler to let your horses graze whenever they want. However, when the grass gets short, your horse has fewer options and will eat more weeds. Many weeds grow better when the pasture is stressed or sparse. Some common weeds that can be toxic to horses are Russian knapweed, groundsel or Senecio, houndstongue, locoweed, milk vetch, fringed sage, larkspur and nightshade. Horses will usually not eat these potentially poisonous plants unless they are left with few alternatives.

The best way to prevent plant poisoning is to have a healthy stand of grass. The best way to have a healthy stand of grass is to understand how your grass grows and to manage how your horses graze.

If you need help identifying plants in your pasture, or want some advice on controlling the weeds, contact the Larimer County Weed District at 498-5768 to set up a site visit with a weed specialist.