Nierembergia- Purple Robe- 100 Seeds

I have grown the charming Nierembergia hippomanica "Purple Robe" from seed for decades. It is a super plant with no bug or critter problems and it often overwinters. I have bought it from various sources over the years and I have even harvested my own seed when I could not find anybody selling it. So I believe I know how to grow this plant. The germination rate can be variable: some years the rate is excellent and some years it is only 10-20%. Even with the latter, once the seeds sprout, the plants grow steadily. However, this year that did not happen. From an initial sowing in cells of about 50 seeds, I got only 4 plants and they did not progress to getting their second leaves; they just sat there and after weeks they died. This was not a great year for seed sowing in February, as we had an untoward hot spell, but still even the other plants that struggled at least put out their second leaves. I sowed the rest of the Nierembergia seed packet in late March; the same thing happened, only I had a lot more seed but got only 3 plants. Other flower seeds sown in March went forward, but again, the 3 new plants never put out their second leaves. I think that this seed was weak, possibly from a variety other than Purple Robe. It got to be too late to order more seed (besides which what was available from others was very expensive), so I had no new Nierembergia plants to set out this year. Fortunately, I had 4 plants from last year that overwintered and are blooming now. I will have to harvest seed again this year, I guess.