April showers bring May flowers, but the reverse may also be true. Two studies show that pollen and fungus-generated material broken up into nanometer-sized fragments effectively nucleate water droplets and ice in lab experiments, suggesting that such particles play an important role in seeding clouds and promoting precipitation (Geophys. Res. Lett. 2015, DOI: 10.1002/2015gl064060; Sci. Rep. 2015, DOI: 10.1038/srep08082). Researchers had previously looked at micrometer-scale pollen grains and fungal spores and concluded that they were too large in size and too few in number to have much effect on clouds. Breaking up the material into bits, however, changes the equation. In one study, a team led by Allison L. Steiner of the University of Michigan looked at how pollen fragments from ragweed and several trees can nucleate cloud droplets. In the other study, a group led by Daniel O’Sullivan and Ben J. Murray of the University of Leeds, in England, investigated ice formation from fragments of birch pollen and Fusarium fungus. Including the effect of the fragments in weather and climate change models could help improve understanding of feedback between vegetation and clouds.