We’ve been starting our cucurbit (squash family) seeds indoors under lights to get a leg up on the season for a few years. Last year, we noticed that the germination rate for these seeds was unusually poor. This was brought into painful focus when only 1 of 33 of our Baby Bear pumpkin seeds germinated. A clue presented itself when we noticed that this pumpkin variety was the only one of our cucurbit seeds that was offered as treated seed.
Following our notes from last year, we started all our cucurbits in sterile soil this year. The results are now in, and they are striking. The one-to-one comparisons are shown in the table below. Each of the varieties shown were grown under the same conditions from the same seed from the same source for that year (2017 for non-sterile and 2018 for sterile).
[It’s important to note that we start most of our indoor seeds in sterile soil. In fact, we sterilize compost and make our own soil mix using coir, sand, vermiculite, wood ash and organic fertilizer. However, we decided to risk the non-sterile mix for the cucurbits because we start them just 2 weeks before they’re planted in the garden and they seem like such robust seeds.]
On average for all the cucurbit seed, the germination rate went from 53% for non-sterile soil to 94% for sterile soil. As for the pumpkins, we opted for the treated seed this year… and the germination rate went from 3% to 83%.