Geraniums are popular bedding plants used in urban public space and private gardens. Although well adapted to drought they often suffer from water stress, especially when planted into containers. In this trial, a response to periodical soil water shortage was tested on potted geraniums fertilized with a fertilizer containing 36% silicon and 20% phosphorus. During five weeks of culture under the experimental conditions, half of the greenhouse-grown plants were subjected to two 7 and 10-day periods without irrigation, separated by the periods of standard watering (7 and 10 days, respectively) (stressed plants) while the other half were irrigated (control plants). Half of the plants in each watering regime were planted into a growing medium enriched with the Si+P fertilizer. The parameters of growth and flowering were evaluated on the 35^th day and the leaves were analyzed for RWC, chlorophyll a+b and free proline contents. Water stress had little effect on plant height but decreased by one third the fresh weight of the above-soil plant parts. The number of flowers remained unaffected but the number of flower buds developed under the experimental conditions fell to 30% in plants subjected to stress as compared to the watered control. The application of the fertilizer enhanced plant growth regardless the watering regime but decreased flower numbers in both groups. However, this treatment positively affected development of new flower buds, especially in stressed geraniums, where the increase in bud number was nearly 8-fold relative to the non fertilized plants. The relative leaf water contents remained unaffected by the watering regime while the fertilizer increased RWC in both plant groups. Total chlorophyll contents doubled under stress, and were further increased by the fertilizer in both plant groups. Water deficit increased the free proline content in leaves by a third. However, in the non-stressed and fertilized plants it increased by 48% and remained unchanged in stressed fertilized plants. The experiment demonstrates that Si+P fertilization may mitigate the undesirable effects of water-stress in potted geraniums.

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