Nutrient availability limits phytoplankton growth throughout much of the global ocean, and this has led scientists to consider fertilizing the ocean with phytoplankton growth‐limiting nutrients. We studied the response of phytoplankton to the addition of natural materials such as rice husk and bamboo leaves through field mesocosm experiments. Rice husk released only SiO 4 4− while the bamboo leaves released SiO 4 4− and also N...