The effects of three slow-release fertilizers on the growth, development and the abundance of flowers were compared for six cultivars of New Guinea Impatiens: ‘Hot Rose’ and ‘Salmon’ from the Petticoat group, ‘Pink’ and ‘Deep Salmon’ from the Riviera group and ‘Moala’ and ‘Moorea’ from Paradise group. The following fertilizers were applied: Osmocote Plus at the dose of 5 g·dm⁻³, Osmocote Exact at the dose of 5 and 7.5 g·dm⁻³ and Polyon at the dose of 2.5 and 5 g·dm⁻³. Sphagnum Peat, neutralized with chalk and dolomite to pH 6.2 was used as a medium. Growth dynamics, plant diameter, habit, and flowering were evaluated. NGI responded favourably to all the applied fertilizers, although to different extent depending on the cultivar. The plants were of appropriate compact habit, well branched and maintained high decorative value for a long time. Taking into consideration 4-5 month flowering period the most favourable effects on the flower abundance were observed in the case of higher doses of Osmocote Exact and Polyon and Osmocote Plus at the dose of 5 g·dm⁻³.