Hello all,

Common advice, here and elsewhere, is to use a sterile medium for seed starting. However, there's a body of research building up that suggests certain kinds of biologically active media may be beneficial to suppressing damping off and other diseases. I've been personally experimenting with using vermicompost (worm poop) and mycorrhizal inoculants in my seed starting mixes, with good results so far.

Researchers have shown that vermicompost can suppress fusarium wilt ( M. M. Szczech 2008 ) and pythium fungi, along with other diseases (Chaoui and Edwards et al. 2002; Simsek-Ersahin 2010). There's also evidence that vermicompost in seed starting mixes can increase germination rates for at least some species (Arancon and Edwards et al. 2008; Zaller 2008 ), although there've also been some papers suggesting reduced germination (Ievinsh 2011). Some of this variability may be due to the wide range in composting feedstocks, and resulting differences in chemical and microbial properties of the processed material.

Mycorrhizal fungi refers to fungi that live in mostly symbiotic relationships with plant roots. There are some studies showing disease suppression from inoculation with these fungi (Chandanie and Kubota et al. 2009; Calvet et al. 1993), as well as a growing body of literature suggesting benefits to plant growth. See Artursson et al. (2005) for a review.


My living space is in an old building in a heavily polluted area, and germinating plants in sterile media was a constant losing struggle with damping off diseases. I've had much greater success since switching to my current seed starting mix of equal parts vermicompost, coarse sand, and pumice - perlite would do as well - inoculated with a mycorrhizal mix ("Myconox" brand). I've lost very few seedlings with this composition. It does drain freely, so some attention is required to watering.

In general, there's a shift happening in the agronomy world towards an awareness of the importance of microbiology and trophic interactions in the soil, and that by thinking of microbial factors in addition to agrochemistry we can grow healthier plants with fewer inputs. "Teaming with Microbes" is a popular general audience book about of this idea.

Has anyone else here experimented with seed mixes with high levels of microbial activity? From my experience I think it's worth trying for anyone struggling to keep seedlings alive.