This one is tall, with red stems and clusters of flowers of a purple Caesar would envy. As fast as we see improvement in pastures we are beginning to graze intensively, a glance at the fields in July and August is always a little discouraging; iron weed can grow to as much as ten feet , and it self-sows generously. Neither the cows nor the sheep will browse it significantly. Additionally, according to Ohio State, “research showed that 9 successive years of mowing on two dates during the year caused no significant stand reduction of tall ironweed. Herbicides controlled top growth of tall ironweed in the season of application but had little effect on regrowth from surviving roots.”
Good news: intensive grazing seems to be much more effective than that. After six years, where once the iron weed grew thick and tall, our home pastures now show only a few scattered plants. Why should intensive grazing work when mowing does not (after all, the animals aren’t grazing the iron weed, just its companion plants), and why might the process take a few years to show its effectiveness? We’re not experts, but we speculate that individual plants already established continue to push through the pasture grasses for several years until either their viability is sufficiently compromised by competition, or until they have completed their natural life cycle, while new plants can’t get established through the improved ground cover that goes with intensive grazing.