Tomatoville® Gardening Forums - View Single Post - Diatomaceous Earth as a seed starting medium

RayR · August 7, 2012

I haven't had any damping off problems with DE. I've seen a number of references about professional growers who use silicate minerals, mainly coarse sand or crushed granite (bird grit) as a top layer over a seed starting medium to prevent damping off. I've done this myself with great results, the only times I've had any damping off problems was when I was using seed starting mix alone. I've seen a recommendation from a hydroponics grower to use DE as a top layer over seed starting medium for the same reason. I don't know if the effectiveness is due to a dryer surface or if the mineral layer is just inhospitable to the growth of damping off pathogens, maybe both, I don't know for sure, but it seems to work well.

There is some fine dust even with the granular DE, but not bad and only when first pouring it out of the bag. Misting it good with water will eliminate any dust kick up when filling your cells.

I judge the bottom watering by the color of the top surface, when the DE is getting dry it appears very white, when it is moist it turns darker and the earth tones come out.

It'll be interesting to hear your results.

August 7, 2012	#57
RayR Tomatovillian™ Join Date: Jun 2010 Location: Cheektowaga, NY Posts: 2,466	I haven't had any damping off problems with DE. I've seen a number of references about professional growers who use silicate minerals, mainly coarse sand or crushed granite (bird grit) as a top layer over a seed starting medium to prevent damping off. I've done this myself with great results, the only times I've had any damping off problems was when I was using seed starting mix alone. I've seen a recommendation from a hydroponics grower to use DE as a top layer over seed starting medium for the same reason. I don't know if the effectiveness is due to a dryer surface or if the mineral layer is just inhospitable to the growth of damping off pathogens, maybe both, I don't know for sure, but it seems to work well. There is some fine dust even with the granular DE, but not bad and only when first pouring it out of the bag. Misting it good with water will eliminate any dust kick up when filling your cells. I judge the bottom watering by the color of the top surface, when the DE is getting dry it appears very white, when it is moist it turns darker and the earth tones come out. It'll be interesting to hear your results.