Abstract. Gerbera hybrida is an ornamental plant of great commercial interest, which
is primarily propagated by seeds. We investigated whether increasing fertilizer
concentrations during seed set enhanced plant biomass, number of flower heads, seed
set, and seed weight. Furthermore, we studied whether an additional foliar calcium
application influenced the same parameters. Subsequently, the effect of the various
treatments on the germination of the obtained seeds was explored. Two identical
experiments (A and B) were carried out with five concentrations of nutrient solutions
corresponding to an electrical conductivity (EC) of 1.25 mS·cmL1, 2.50 mS·cmL1, 3.75
mS·cmL1, 5.00 mS·cmL1, and 6.25 mS·cmL1. Additionally, plants were sprayed with
a 0.5% foliar-applied calcium solution or deionized water (control) three times
during the experimental period. In Expt. A, the concentration of fertilizer significantly
affected seed production. Number of flower heads and seed weight were not
influenced by the dose of fertilizer, but plant biomass and number of seeds were
significantly reduced at the highest concentration (6.25 mS·cmL1). In Expt. B, the
fertilizer concentration did not affect number of flower heads and seed number, but
seed weight and plant biomass were significantly reduced at the highest fertilizer
concentration. In both experiments, the seeds germinated slower and less seeds
germinated when plants had received the largest amount of fertilizer (6.25 mS·cmL1).
In none of the experiments did applied calcium affect the number of flowers, seed
production, seed weight, or the total biomass. Our data indicate that seed producers
of G. hybrida should not apply standard fertilizer in a concentration higher than
corresponding to an EC of ’1.25 mS·cmL1. It would have been valuable if we also had
included a treatment with a lower EC value like 0.75 mS·cmL1 to improve the estimate
of the optimal EC level from a curved function for the seed production and quality
parameters.