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Plant propagators must take two technological critical decisions: the plug-cell size and the growing medium, both of which have been mentioned as abiotic stress sources for bedding pot plants. However, only a few recent reports on bedding pot plants have simultaneously included limiting and non-limiting plug cell volumes and growing medium during nursery. The aim of this work was to assess the nursery performance of Impatiens walleriana seedlings grown in four plug cell volumes and four growing media with significant differences in both physical and chemical properties. Plants were sprayed or not with an early and single benzyl aminopurine (BAP) dose, aiming to understand how they interact on determining biomass accumulation at the pot transplant stage. The hypothesis tested was that, both plug cell volume and growing medium, must be seen as additive abiotic stress sources, which can be partially overridden by exogenous cytokinin supply. The main result was that, in I. walleriana seedlings, the abiotic stress imposed by the growing medium quality during nursery had a higher effect on biomass accumulation (on both fresh and dry base), leaf area expansion and photo assimilates partitioning than plug cell volume and constitute an interactive process associated with cytokinin synthesis. From a grower´s point of view, one expensive option to avoid root restriction is to use high quality growing media and increase the plug cell volume. In contrast, a single 100 mg L-1 BAP spray can partially override the root restriction symptoms related to abiotic stresses. The novelty of this work is related to the fact that growing media quality would be a more limited factor than plug cell volume for I. walleriana seedlings during nursery.

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Higher bedding plant yields per unit greenhouse area was reaching through two grower´s currently decision-making: plug cell volume during nursery and growing media quality for both nursery and pot cycle. With the goal of maximizing bedding plant yield to identify the main limiting factor at the pot stage, we evaluated Impatiens walleriana yield to the end of the pot growth stage when four different pre-transplant cell volume and four pre or post-transplant growing media with different physical properties were used. The hypothesis tested was that only one of the potentially negative stress source (pre-transplant cell volume or growing medium quality) is the main responsible for decreasing biomass accumulation at the post-transplant pot growing cycle. The experimental design was a randomised factorial with three blocks of five single-pot replications of each treatment combination (plug cell volume × growing medium × pre- and post-transplant).The main result was that, in I. walleriana seedlings, the combining abiotic stresses imposed by both the growing medium quality and nursery plug cell volume defined biomass accumulation (on a fresh and dry base), leaf area expanded and photo assimilates partitioned as opposed to a previous report, which indicate that that growing media quality would be a more limited factor than plug cell volume for I. walleriana seedlings during nursery.