Scientists, corporations, mystics, and movie stars have convinced policymakers around the world that a massive campaign to plant trees should be an essential element of global climate policy. Public dialogue has emphasized potential benefits of tree planting while downplaying pitfalls and limitations that are well established by social and ecological research. We argue that if natural climate solutions are to succeed while economies decarbonize (Griscom et al. 2017), policymakers must recognize and avoid the expense, risk, and damage that poorly designed and hastily implemented tree plantings impose on ecosystems and people.