French marigolds were grown in sand culture with five different P levels (1.1, 5.6, 11.3, 28 or 56 p.p.m. P ) in a Kimura nutrient solution. Plant growth rate increased steadily with increasing P concentration up to 11.3 p.p.m.; above this concentration increases in plant growth rate were slight. No symptoms of P toxicity were observed. The numbers of flower buds and florets increased in proportion to P levels. P concentration had no significant effect on acid phosphatase activity, but analyses of P compounds in treated plants showed that inorganic P concentration increased with plant growth rate.