Nasturtiums are a popular annual flower, prized for their attractive foliage and brightly colored flowers. While seedlings can sometimes be found, most growers plant their own nasturtium seeds. The seeds are fairly easy to grow, and remembering a few simple tricks and tips will help ensure success. Refrigerate seeds that you have collected from the previous year, and soak the seeds in water overnight to speed up germination. Seeds should be planted in a sunny location and do not require much fertilizer.
The first thing to consider when starting nasturtium seeds is whether to use collected seeds or purchased seeds. If you are using seeds that you have collected the year before, they should be stored in the refrigerator for up to two weeks before starting. This simulates the winter season and is important to successful germination. Purchased seeds will not require this treatment.
Planting any kind of flower or vegetable seed is fairly straightforward, and nasturtium seeds are no different. One important thing to take into account is the large size of nasturtium seeds. They are a good deal larger than the seeds of many annual flowers and can be rather slow to germinate for this reason. One way to counteract this tendency is to soak them overnight in water. This will help the seeds germinate much more quickly.
As a tender plant, nasturtium seeds should be started after the danger of last frost in your area. Alternatively, you can start seeds indoors, in any basic commercial seed starting mix, four to six weeks before the last frost. Seeds started indoors should be placed in their containers near a sunny windowsill. For starting seeds outdoors, choose a location that gets lots of sun. Nasturtiums prefer full sun and while they will grow in less well lit areas, they will not produce as many flowers.
Prepare the soil by removing weeds. Fertilizer is not usually necessary as nasturtiums thrive in most poor soils, and an abundance of fertilizer will result in big leafy plants with lots of greenery but few flowers. Whether starting seeds indoors or directly sowing them outdoors, plant the seeds fairly deep, approximately 1 inch (2.5 cm) beneath the soil, and space the seeds about 1 foot (30 cm) apart. Cover the seeds with soil, but do not pack the soil down over the seeds. Water the soil thoroughly upon planting, but do not water again either until the new nasturtium plants appear or until about ten days have passed, whichever comes first.