How late in the winter/early spring can I sow flower seeds using this method? I live in zone 6 and would like to continue sowing annuals and perennials now, in early April. How late can I sow seeds using this method?
You'd need snow. A decent covering. It needs to be around for 4-6 weeks. I don't know how late Spring arrives where you are, but here in Canada it's already too late to begin in most areas.