wintersowing is great. You should have success with any seeds that have sowing instructions: Early Spring, As soon as the ground can be worked, X number of weeks before last frost, etc. Your wintersown plants may be a but small in May, but they will be awesome by June. I have found that wintersown Rudbeckias bloom within 2 weeks of early indoor started ones. So there's an example of time and work saved and just wintersow them. I wouldn't wintersow expensive seeds like petunias. They cab take up to 12 weeks to bloom from germination time. I like to do my wintersowing end of February till end of March. Our average last frost is May 23
