Nasturtium

Nasturtium is not hardy and dies at the first frost in the lowlands of Germany, Austria and Switzerland. Keep it annual: collect ripe seeds in autumn, store them dry and sow anew from mid-April. A container plant you can overwinter instead: cut it back before the first night frost, bring it indoors to a bright, frost-free place and water only sparingly over winter.

Sowing (main method): Nasturtium is a dark-germinating seed. When sowing, cover the seeds with a layer of soil about twice the size of the seed (approx. 1 to 2 cm). The seeds are hard and large; soak them in lukewarm water for a few hours (about 4 to 8 hours) before sowing, which noticeably shortens the germination time and makes germination more reliable. From mid to late April you can sow directly outdoors, as soon as night frosts are no longer a threat; a head start on the windowsill is possible from the end of March/mid-April and brings earlier flowering. At around 18 to 25 °C the first seed leaves appear after 7 to 14 days. If you start them indoors, prick out gently and plant the young plants out only after the Ice Saints (mid-May). In a warm spot nasturtium also self-seeds: ripe seeds fall and germinate the following year. Cuttings (alternative for keeping a variety true): If you want to keep a particular variety or colour true, cut non-woody shoot tips about 10 to 15 cm long during the growing season and insert them into moist, nutrient-poor seed compost. Keep the soil evenly moist without waterlogging and put the pot somewhere warm. New roots often form within the first week. Since nasturtium is frost-sensitive and grown as an annual in Central Europe, cuttings make most sense when you want to overwinter or propagate a favourite plant before the first frost. Layering (for varieties without viable seed): In summer you can lay an outer shoot in a shallow groove in the soil (or in a pot filled with soil placed next to it), cover it with soil and fix it with a stone or a wire staple, so that the shoot tip peeks out at the end. The mother plant keeps supplying the layer while it roots. As soon as the new shoot is visibly growing, it has rooted sufficiently and you can sever the connection. This method is especially worthwhile for special varieties that do not form viable seed.