Nasturtiums ( Tropaeolum spp.) are annual flowers, easily recognized by their vivid, often spurred blooms and distinctive lily-pad-like leaves. The entire plant—from the flowers to the leaves and immature seed pods—is edible, offering a pleasant peppery flavor to salads and garnishes. Cultivating this flower is straightforward, and its seeds sprout quickly. Direct sowing into the garden is the preferred method because the seedlings possess a fragile root system that responds poorly to transplanting.
Optimal Timing for Direct Sowing
The most appropriate time for direct sowing nasturtium seeds is after the threat of the last spring frost has passed. These plants are native to warmer climates and are easily damaged by freezing temperatures. Gardeners should aim to sow seeds one to two weeks following their average last frost date to ensure a safe start.
The successful germination of the seeds relies heavily on soil warmth. The ideal soil temperature range for nasturtium germination is between 55° and 65°F (12° and 18°C). Sowing the seeds into colder soil will delay sprouting or may cause the seeds to rot before they can establish.
To ensure a continuous display of flowers well into the autumn, gardeners can employ a technique called succession planting. This involves staggering the direct sowing of a new batch of seeds every two to three weeks. The succession planting schedule should continue until mid-summer to maximize the blooming period before the first heavy frost arrives.
Preparing the Planting Site
Selecting the correct location determines whether the nasturtium plant produces lush foliage or abundant blooms. Nasturtiums perform best in a site that receives full sun (at least six hours of direct sunlight daily). They will tolerate partial shade, particularly in hotter climates, but plants grown there tend to produce fewer flowers.
Nasturtiums thrive in poor, well-draining soil. The common gardening practice of amending soil with rich organic material or high-nitrogen fertilizer should be avoided. Soil that is too fertile encourages excessive vegetative growth, resulting in lots of leaves at the expense of colorful flowers.
Before sowing, the planting area should be cleared of any weeds or debris that could compete with the new seedlings. The top few inches of the soil should be lightly loosened to a fine, crumbly texture for easy seed placement and initial root penetration.
The Direct Sowing Process
To encourage a quicker start, the hard outer shell of the nasturtium seed can be softened before planting. Soaking the seeds in lukewarm water for 12 to 24 hours prior to sowing speeds up germination. This hydration softens the seed coat, allowing moisture to penetrate the embryo.
The seeds should be planted at a depth of one-half to one inch and covered completely with soil, as darkness is required for germination. Spacing depends on the variety chosen; compact, bushy types can be spaced 8 to 12 inches apart. Trailing or climbing varieties require more room, sometimes needing up to 36 inches of space.
Immediately following sowing, the soil needs to be thoroughly watered to settle the seeds and initiate germination. Consistent moisture is required until the seedlings emerge (typically within seven to fourteen days). Once the young plants are established, their watering needs decrease, and they prefer drier soil conditions, though they should be watered during extended dry periods.