Experiments were conducted in Mayagüez, Puerto Rico, to determine the effect of two biostimulants on the in-nursery growth of grapefruit budded on 'Cleopatra' rootstock. A kelp (Ascophyllum nodosum) extract (Stimplex®) and a commercial mixture of amino acids (Macro-Sorb Radicular®) were drenched at several rates, starting one month after budding and repeating the applications every 10 days until the plants reached the adequate transplanting stage. Biostimulant-treated plants attained the adequate transplanting stage earlier than untreated plants. 'Duncan' and 'Marsh' responded equally to the biostimulants, and the extent of growth response was greater as the biostimulant rates increased. These results indicate that both biostimulants may be useful to accelerate the production of 'Duncan' and 'Marsh' grapefruits budded on 'Cleopatra' rootstock.
