Abstract: The present invention relates to methods for injecting desired amounts of fluids into plants, in particular embodiments, woody plants, e.g., trees and woody vines. A metering device is provided which dynamically measures an amount of fluid that is injected into the plant. A system and method are also provided for creating a pressurized reservoir of injectable fluid in the plant to assist in the injection of the fluid. A pressure release valve is also provided to prevent overpressurization of the pressurized reservoir of injectable fluid. In one embodiment, fluid is returned to a metering device of an injection system when the pressure within the pressurized reservoir exceeds a predetermined amount of pressure. A pressure gauge is also provided that measures pressure within the plant. A falling pressure indicates that fluid is being injected into the plant. Manual and battery-powered plant injection devices are also provided.