Nasturtiums are popular garden annuals, celebrated for their vibrant, edible flowers and lily-pad-like foliage. While generally easy to grow, their germination can be slow and inconsistent, which is a common frustration for home gardeners. This difficulty stems from a protective biological mechanism within the seed itself. Preparing the seed through “nicking,” or scarification, is the most effective way to overcome this hurdle and ensure a successful start.
Why Nasturtium Seeds Require Preparation
The low germination rate of nasturtium seeds is a direct result of their tough, water-impermeable outer shell, known as the seed coat. This dense covering creates physical dormancy, a natural survival strategy. The hard shell prevents the seed from absorbing moisture too quickly, protecting the delicate embryo inside from germinating during an untimely rain shower.
For germination to begin, the seed must absorb water, a process called imbibition. This signals to the plant embryo that conditions are right to sprout. The thick seed coat resists this process, often requiring prolonged exposure to soil moisture to naturally break down. By physically altering the seed coat through nicking, a gardener bypasses the natural defense mechanism, allowing water to penetrate the seed and trigger rapid germination.
Detailed Steps for Nicking the Seed Coat
The process of scarification, or nicking, involves creating a small breach in the seed coat using a sharp tool. Common implements include nail clippers, a small file, or coarse sandpaper. Since the nasturtium seed is relatively large, resembling a wrinkled pea, it is easy to handle and locate the spot for the incision.
To perform the nicking, hold the seed firmly and identify a spot along the curved side. Take care to avoid the small, dark spot (the hilum), which is close to the embryo. The goal is to make a shallow cut, just deep enough to break through the hard outer layer without damaging the soft, lighter-colored tissue inside. A successful nick will look like a slight opening or a small, pale scratch on the dark seed surface.
If using nail clippers, gently clip a tiny segment from one edge of the seed. If you opt for a file or sandpaper, rub a small corner of the seed coat until the lighter inner layer is barely exposed. Work slowly and be mindful of the tools, as the force needed to break the coat can sometimes cause the seed to slip. This intentional weakening of the seed coat ensures maximum water absorption while minimizing the risk of harming the developing embryo.
Immediate Steps After Scarification
Once the seeds have been nicked, the immediate step is soaking them in warm water. Placing the scarified seeds in tepid water for 8 to 24 hours allows for thorough imbibition, where the seed rapidly takes up the moisture needed to begin metabolic processes. Seeds that swell noticeably are absorbing water successfully and should be planted immediately.
After soaking, the prepared seeds should be sown without delay, as drying out at this stage can be detrimental to the now-activated embryo. Plant the seeds shallowly, covering them with about one-half inch of well-draining soil or seed-starting mix. Nasturtiums prefer full sun to partial shade and thrive in soil that is not overly rich. Keeping the soil consistently moist and warm (ideally 60–70 degrees Fahrenheit) encourages quick sprouting, often within seven to ten days.