I usually sow seeds of Tropaeolum polyphyllum[i] in deep pots (6 inches minimum or as deep as you like) with the seeds about an inch below the soil surface. I sit the pots outside for the winter, protected from birds and mice. On germination, the roots rush to the bottom of the pot and, with luck, form small tubers there. Sometimes the tubers form actually in the drainage holes of the pot, which can mean cutting up the pot to extract them. When the seedlings go dormant, these small tubers can be planted out or potted on into larger pots to grow on for a further season or two. I have never yet tried sowing seed directly into the open ground, but there is no reason why this should not work perfectly well as long as there is sufficient depth of soil for the roots to develop (yes, they can go down one metre) and it is well-drained. The important thing to remember is that, though this species can cope with conditions 10,000 feet up in the Andes, the tubers cannot tolerate frost, therefore tubers must be planted deeply and tubers grown in pots must be adequately protected through the winter. The seeds, however, seem to benefit by stratification. I hope this is helpful. T.polyphyllum is a wonderful species, so good luck. Graham.
