Nasturtiums are popular annuals known for their vibrant flowers, lily pad-like foliage, ease of growth, and versatility. They quickly create colorful borders, ground cover, or trailing displays. Their edible leaves and blossoms add a peppery flavor to salads. Sowing nasturtium seeds directly into the garden is a straightforward process that results in a rewarding display of orange, red, and yellow hues throughout the summer season.
Preparing the Planting Site and Seeds
Sowing time depends on soil temperature, as nasturtiums are sensitive to cold. Plant them outdoors only after the danger of the last spring frost has completely passed. The soil needs to be warm, ideally between 55°F and 65°F, to encourage strong germination. Locating the planting site in full sun, where plants receive at least six hours of direct sunlight daily, will result in the most abundant flowering.
Nasturtiums thrive in average to poor, well-draining soil; rich, highly-fertilized soil should be avoided. When the soil contains too many nutrients, the plants produce abundant foliage rather than colorful blooms. If the planting area has heavy, compacted soil, amending it with sand or mature compost can help improve drainage and texture.
The seeds have a hard, thick outer coat that can delay water absorption and germination. To accelerate this, pre-treat the seeds by soaking them in warm water for four to eight hours prior to planting. This process softens the seed coat, allowing moisture to penetrate and trigger the embryo inside. Alternatively, the seed coat can be nicked with a nail clipper or file, which achieves the same result of weakening the hard exterior.
Direct Sowing Steps
Direct sowing outdoors is the recommended method for nasturtiums because their root systems are delicate and respond poorly to being transplanted. Once the planting site is prepped and the seeds have been soaked, sow the seeds at a depth of approximately one-half to one inch into the prepared soil.
The required spacing depends on the variety of nasturtium being grown. Bush or mounding varieties, which remain compact, should be spaced 10 to 12 inches apart to allow for proper air circulation and growth. Vining or trailing varieties spread more aggressively and may require 24 to 36 inches of space between plants.
After placing the seeds, gently cover them with the surrounding soil and lightly pat the surface down to ensure good seed-to-soil contact. Immediately water the planting area thoroughly. This initial watering helps settle the soil around the seeds and provides the moisture necessary to begin germination.
Post-Planting Care and Germination
Maintaining consistent, even moisture in the soil is important until the seedlings emerge, but the soil should never become waterlogged. Nasturtium seeds generally sprout within 7 to 14 days; pre-soaking often leading to faster germination. Once the seedlings are established, the mature plants become relatively drought-tolerant, requiring less frequent watering.
When the seedlings have developed their first set of true leaves, thin them out if they were planted too closely. Thinning involves selectively removing the weaker seedlings to leave only the strongest plants at the recommended spacing. Overcrowded nasturtiums compete for light, water, and nutrients, resulting in fewer flowers and a less impressive display. Adequate space ensures they receive the resources necessary to mature into healthy, colorful flowering plants.