Depending on the temp in your ziplog bags, also if the sunlight comes (through the window) over the bags, if the temp was too high you cooked the seeds.
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If not, maybe too low.
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I used too this method (slightly different, not in a bag, but in a box, covered) and maybe I am not skilled enough or what, but I think will use no more. I have the feeling the plants grown this way are not so health (or at least as seedlings). I am using something from supermarket, some cells, where I put the soil, not filling them completely, watering, put the seeds, put a transparent cover. When the seeds start to sprout, I cover them with a tiny layer of soil. This way I can see if they are sprouting, and they grow directly in that soil.
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Put some picture, maybe will give a hint to somebody (a picture worth more than 1000 words).