I use 'sterile' ingredients. I dig topsoil from the second spade down or else buy loam with a clay content, designed for cricket pitches and tennis courts, I sometimes use concrete (coarse)sand, I buy peat or "multipurpose" (humus based) compost, I make leaf mould from hedge clippings and leaves which I am careful not to put seeds of weeds such as grass or bluebells in -or plants such as Ranunculus ficaria, and the grits I buy are effectively sterile too, 3-6 mm "Horticultural Grit" is cheapest at around £2.00 for 25 K but finer grits are sometimes better (and are more expensive) in the mixes the cheapest of these are Dashing Grits. I use 6 or 10 mm gravel for topping. I have considered buying a steriliser (Heat) in order to sterilize used compost, (and heat the greenhouse), but I haven't done this yet. My main mix contains ratios of perhaps 3 bags 6mm grit, 2 bags 2-3mm grit, 1 bag coarse sand, 4 bags loam and 2 bags JI no 3 or "Top Soil" (both products have become very high in humus now). I add fertiliser. Essentially this mix is 50/50 aggregate to soil. I then mix in humus as required and sometimes extra sand, I plant both seeds and bulbs in this, Trilliums would get an equal volume of humus and leaf mould , crocus would get about 1/3 leaf mould and extra sand. most Alliums, leontocoides Corydalis, Rhinopetalums, scree dwellers and Tulips would get the 50/50 mix, as would most junos though a few get extra humus (eg aucheri, cycloglossa..) Peter (UK) On Wed, Jul 11, 2012 at 7:49 AM, Bulborum Botanicum <bulborum@gmail.com>wrote: > Hello Peter > > How do you sterilise larger quantities seeding mixture >