Evaluation of the condition of three hundred and sixty eight rose cultivars in the Rose Collection of the Botanical Garden of PAS in Warsaw after the winter 2009/2010

The resistance to frost and winter conditions is a very important aspect of plant and rose cultivation in the Polish climate. The number of new cultivars from around the world available in Polish nurseries is constantly on the increase. The collection of roses in the Botanical Garden of PAS was founded in 1998. There are more than six hundred and ninety taxa and culta of all groups of garden roses. This paper describes the evaluation of the condition of three hundred and sixty eight cultivars from different groups (hybrid teas, floribundas, polyanthas, shrubs, miniatures, climbers and ramblers) after the long, cold and snowy winter of 2009/2010. These were from the Botanical Garden’s collection budded on various rootstocks or those growing on their own roots (two cultivars only). All the shrubs were covered for the winter. In spring 2010 injuries and winter frost damage to the shrubs were observed according to the scale of frost damage to deciduous plants by ukasiewicz (1992) and height of damage above ground level. At the first moment of flowering observations were made on the height of shrubs and the valuation of flowering according to a fixed scale. All damaged shrubs were evaluated according to the ukasiewicz scale from 4 (one-year-old shoot tips frozen) to 7 (shoots frozen to the ground but new shoots produced from the undamaged part of the plant) and several cultivars to 10 (the entire plant frozen). Shrub roses, ramblers and climbers over-wintered quite well. The most severe damage was to hybrid teas, floribundas and miniatures. Most of them were cut to ground level. Climbers and ramblers flowering on two-year-old shoots suffered the heaviest loss of ornamental value. For ninety four cultivars from different groups the frost damage didn’t have any negative impact on their ornamental qualities during the vegetative season.