Seeds lose viability quickly. Preferably sow with fresh seed in the autumn into pots or pans of standard loam based seed compost with added sharp sand (horticultural sand)
at a ratio of 2parts compost to 1part of sharp sand. Lightly cover with grit sand and place into a cold frame. Germination may take up to 2months.

Peter.

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Thank you very much, Peter, but that was what I do! I had many nice seedlings and have been very, very careful for them. But then came the winter, where I stored them in the garage in order to avoid frost and too much humidity. Even, I never gave them water the whole winter. And then, in the spring, nothing came back. All the nice seedlings were lost! And that's what I wouldn't experience again. What did I wrong?
rosacentifolia