Nasturtiums are popular garden annuals prized for their versatility, vibrant blooms, and ease of cultivation. These cheerful plants feature lily pad-shaped leaves and showy flowers that range from buttery yellow to deep mahogany. All parts are edible and possess a delightful peppery flavor. Planting nasturtium seeds directly into the garden is a straightforward process that encourages robust growth and a plentiful harvest of both foliage and flowers.
Site Selection and Soil Requirements
Selecting the correct location is crucial, as nasturtiums have specific light and soil preferences that differ from many common garden plants. These flowers perform best in full sun (six or more hours of direct sunlight daily), though they can tolerate partial shade, particularly in regions with intense summer heat. Full sun promotes the most prolific flowering; plants grown in shadier conditions often produce more foliage at the expense of blooms.
The timing of planting is critical, as nasturtiums are not tolerant of frost and should only be sown outdoors after the last expected frost date has passed. For optimal germination, the soil temperature should range between 55 and 65 degrees Fahrenheit. Nasturtiums prefer poor or average soil conditions that are well-draining, rather than rich, fertile ground.
Enriching the soil with too much organic matter or fertilizer can lead to an undesirable outcome. Highly fertile soil encourages the plant to produce abundant, lush foliage, meaning the gardener will see a canopy of leaves with very few flowers. The goal is to avoid fertilizing and instead use average garden soil with good drainage, which prioritizes flower production over excessive vegetative growth.
Preparing Seeds and Direct Sowing
Nasturtium seeds possess a hard, protective outer coat, which can delay or prevent water absorption and germination. Gardeners often prepare the seeds by either soaking or scarifying them before planting. Scarification involves lightly nicking or scratching the tough seed coat with a nail clipper or sandpaper, which allows moisture to penetrate more easily.
Soaking the seeds in lukewarm water for four to twelve hours helps to soften the shell and kickstart water intake. Seeds that float after soaking are sometimes considered non-viable, but it is recommended to plant them anyway, as some may still germinate successfully. Direct sowing into the garden soil is preferred over starting them indoors because their fragile root systems are sensitive to transplanting shock.
Once the seeds are prepared, they should be sown 1/2 to 1 inch deep into the prepared soil. Spacing varies depending on the variety selected, as nasturtiums are divided into compact bush types and vining types. Bush varieties require 6 to 12 inches between seeds, while vining varieties may need up to 12 inches or more between planting points.
Establishing New Nasturtium Plants
Consistent moisture is essential immediately following planting for successful germination. After sowing, water the area deeply and thoroughly to settle the soil around the seeds. The soil must be kept consistently moist—but not waterlogged—until the seedlings emerge, which typically occurs within seven to fourteen days, depending on the soil temperature.
Once the seedlings have developed their first set of true leaves, they are considered established and require less attentive watering. If the seeds were sown too closely together, the emerging seedlings may need to be thinned to the recommended final spacing. Thinning involves carefully removing the weaker seedlings, leaving the strongest plant at each desired location.
Seedlings should be monitored closely for early signs of pest pressure, particularly from aphids, which are often drawn to the new, tender growth of nasturtiums. Nasturtiums are frequently used as a “trap crop,” meaning they attract pests away from other garden vegetables. A strong blast of water from a hose can often dislodge and control small infestations on young plants.