<p>Hardy geraniums (<i>Geranium</i> spp.) are popular perennials valued for their ornamental traits. As the ornamental industry constantly seeks novelty, breeding remains a driving force for the development of new cultivars. Polyploidization offers several advantages, including phenotypic modifications (e.g., altered leaf and flower size) and fertility restoration. This study aimed to induce polyploidy in two hardy geranium genotypes, <i>Geranium</i> ‘Sanne’ and <i>G. sanguineum</i> ‘Blushing Turtle,’ selected for their ornamental value and strong regeneration ability. Various concentrations of colchicine, oryzalin, and trifluralin were applied to in vitro plantlets in solid and liquid media. Ploidy levels were then assessed using flow cytometry. <i>G.</i> ‘Blushing Turtle’ showed a lower mortality rate after antimitotic treatment and a lower incidence of polyploidy compared to <i>G.</i> ‘Sanne’, but it did not yield any acclimated chromosome doubled plants. In contrast, <i>G.</i> ‘Sanne’ produced seven chromosome doubled plants out of 270 treated explants. Six of these were induced by trifluralin at concentrations of 3 and 6 mg.L^− 1 in a solid medium and one was induced by oryzalin at 10 mg.L^− 1 in liquid medium with a 24&#xa0;h exposure time. Morphological alterations in the chromosome doubled plants were clearly distinguishable from the control group. Statistical analysis showed increased flower diameter and style length in chromosome doubled plants, while flower number and flowering time remained unchanged. Notably, the fertility of three of these plants was restored, enabling the initially sterile <i>G.</i> ‘Sanne’ to produce seeds. This outcome provides breeders with new opportunities to expand the hybridization potential of future hardy geranium cultivars and introduce novel trait combinations.</p> Graphical Abstract <p></p>