When I sow scorzonera indoors, it germinates well enough. But it doesn't take well to being transplanted. So I sow it in large patio pots (for ease of harvesting); germination is poor, and still most of the plants wither. Is the soil too damp, or too dry? There seems to be no leeway between the two. The local soil is clay, so I'm using compost made largely from forest wastes, mixed with sand. Should I try vermiculite or something else?