Understanding how a plant grows through the grazing season is the key to figuring out when grazing it will make the most impact. The problem is that you have lots of different plants in your pasture, and so you also have to think about the ones that you’d like to have more of, and which ones you’d like fewer of. In addition, you also have to know whether your animals know that a particular plant is edible, and then factor in that they will be choosing what to eat based on how the plant meets its nutritional needs. It’s a balancing act, and as with all balancing acts it takes time and practice to be successful. To get you started, here are some of the grazing and growing balance points to keep in mind.
Most plants tolerate early-season grazing because that’s when soil moisture and nutrients are most abundant. They get grazed down, no problem! Their roots dig in a little, suck up what they need to grow and, TA DA!, new leaves! Growing new leaves is also easier because plants are still short in the spring so their growing tips (apical meristems) are close to the ground and are unlikely to be bitten off.
Plants that you’ll be able to control with spring grazing are those that have a short lifecycle and mature very early. Examples include Kentucky bluegrass, cheatgrass and medusahead grass. Because they green up and may even have finished their lifecycle before other plants have begun to grow, grazing these species in the early spring can help you make progress in controlling them. There’s an upside to this early grazing as well. You have plants that provide forage just when you’re tired of feeding livestock and grazing these “early bloomers” means you’re not damaging the forages you’ll need later in the season. Just be aware of when your other forages start growing so you can move your livestock on when necessary.
Plants are most susceptible to damage from grazing as they start to elongate in preparation for flowering. In forbs, this is called the bolting stage. In grass, it’s called boot stage. Plants are susceptible at this time in their growing cycle because they’ve put so much of their energy into reproduction. They can and do regrow if they’re bitten off but it takes a little more time. Growing points have to be recreated and that’s hard if it’s at the heat of summer and there’s not as much precipitation or soil moisture. Plants have also invested a lot of energy in creating bigger leaves that grab lots of sunshine, and photosynthesize to support a larger root system. Remove those leaves and the plant has to cut back on roots that no longer have enough energy coming in to keep them going.
If you’re trying to try to reduce weed populations it makes sense that you’d graze them as they’re beginning to develop buds. But you also want to time your grazing so that you’re not hitting plants, like grasses, that you’d like to have more of. Fortunately, grasses have often completed their life cycles and gone dormant, just about the time your weeds are bolting. One of the things you might see when you graze weedy plants like thistles or knapweeds is that they sometimes push out 2 blooms for every one a cow bites off. That seems scary, but what some research is starting to show is that the second round of blooms produce many fewer viable seeds. So graze away.
Studies have also shown that if you really want to make an impact on a plant you have to graze it more than once in a grazing season. You can think of this as a problem, or as an opportunity for more forage. You can graze weedy species, like spotted knapweed or yellow starthistle when they bolt, and then when they bolt again and after your grasses or preferred species have completed their seed production.
Once a plant has gone to seed and becomes dormant it’s done for the season, and grazing does little harm. Note that I didn’t say grazing in the dormant stage causes NO harm. That’s because you still need to protect plant crowns so that in the spring they have enough energy to grow again in the spring. Some studies show that it is possible to overgraze in the winter. You know enough about how things work to know that if you slick off your pasture in the winter, there are probably going to be spring time consequences.
Do Your Livestock Know What to Eat?
Of course, grazing to manage vegetation is a moot point if your livestock don’t know that weeds are good forage. I’ve been sharing information about that for some time now. Here’s a link if you’d like to make sure your livestock are prepared to become your vegetation managers.
I’ve put together examples of grazing to control leafy spurge, spotted knapweed and Canada thistle. Read more about it here.