We're talking a type of thistle, the kind that open up and emit those round cottony looking things with a seed attached, so light that they billow in the air even on a still day. Some are opening today, but 95% are in the bud stage. I'm pulling them from vegetable planting beds, and instead of throwing them over the hill I thought I'd use them as mulch on the garden beds. Should I be concerned that the underdevelopped seed in the flower head may be viable? Don't want to add weed seeds to my vegetable garden. Asking this question on the organic gardening forum also.