At about the end of June I scarred about 200-300 open pollinated HT achenes in a mixture of 3% hydrogen peroxide in a 1/3 cup of water (soapless mixture A of Don’s guide) for about 12 hours and I sowed them outdoors in seed trays. The temperature did fluctuate between an average of minimums of 3-7C (there were few days that reached 0-3C) and daily highs of 15-21C. About 70 days later I now have 30 seedlings and more are still coming up.
I’m quite happy with the results, the germination rate is currently somewhere between 10-15%. If I get any more hips which are open pollenated I’ll test them in summer conditions.