The present invention relates to the promotion of the growth of at least one plant by providing a fertilizer composition-comprising at least one zeolite, into the pores of which at least one basic L-amino acid has been adsorbed； adding the fertilizer composition to a medium for plant growth； and culturing a plant therein. The invention will provide the release of nitrogen from the fertilizer composition during culture of the plant at a rate which is advantageously used by the plant. The invention also relates to a fertilizer composition as such, optionally combined with a medium for plant growth to make up a growth-promoting material. The invention is advantageously used to reduce the resources required in the fertilization of slowly growing plants, where repeated supply of nutrients as well as leakage of nitrogen amounts to large costs to society.
