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Shine a light on issues that matter—support local news with your gift today. As spring approaches, landowners and conservationists may be considering prescribed burns on Conservation Reserve Program (CRP) acres. While an early burn may satisfy contract requirements and clear the way for other projects, the timing can have significant effects on both native and invasive vegetation. "The dog days of March, before field work begins, are a popular time to complete required burns on CRP acres," said Greg Schmitt, private lands biologist with the Iowa Department of Natural Resources, in a release shared earlier this month. "But what is the impact on desirable vegetation that doesn't start growing until the ground warms? And could an early burn actually encourage invasive species like Canada thistle or volunteer trees?" Understanding Soil Temperature and Vegetation GrowthAccording to Schmitt, native warm-season prairie vegetation generally starts growing when soil temperatures at four inches deep reach 50 degrees, whereas invasive species like Canada thistle and smooth brome begin growing at around 45 degrees. "All springs are different, and soil temperatures can fluctuate," Schmitt explained. "I've seen temperatures jump to 50 degrees for a few days and then fall to 45 degrees for weeks before rising again. That was a very bad year for Canada thistle." Burn Timing and Tree GrowthWhen it comes to controlling unwanted trees, Schmitt noted that timing is critical. Burning before leaf-out does little to impact established trees. "The tree will resprout with a vengeance, using its energy reserves to create new stems and leaves," Schmitt said. "However, a prescribed backburn conducted after leaf-out—typically in early May—can severely stress the tree, depleting its underground energy reserves and limiting its ability to recover." However, for CRP compliance, prescribed burns must be completed before May 14 to avoid disrupting the primary nesting season for ground-nesting birds. Balancing Grass and Flower GrowthLate spring burns tend to benefit native grasses while setting back wildflowers, particularly in stands dominated by grasses. Schmitt emphasized the importance of a balanced seed mix. "The best way to prevent grass dominance is to plant a diverse 20/20 mix with equal amounts of grass and flower seeds," he said. "Pollinator CRP mixes typically contain 10 grass seeds and 30 flower seeds per square foot, making them more resistant to grass overgrowth—even with later burns." Making the Right DecisionUltimately, the best timing for a prescribed burn depends on site conditions and management goals. "If trees and weeds are present, a slow backburn in early May is the best approach," Schmitt advised. "If the CRP stand is surrounded by trees, has a history of Canada thistle, or is dealing with brome encroachment, late April to May 14 is the best window to burn. Burning too early, before soil temperatures reach 50 degrees consistently, could create openings for thistle and tree invasion—leading to more work and expense down the road." For more information on prescribed burns and CRP management, visit www.iowadnr.gov. Stay informed, stay inspired! Newsletter sign up is free and join hundreds of free subscribers who rely on DecorahNews.com for trusted information and fresh perspectives.

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Timing a Prescribed Burn on Prairie CRP: Too Soon or Just Right?