Finding your nasturtium seeds floating in the water can feel like a botanical verdict of guilt, as if the seed itself has raised a tiny white flag of surrender. It is a common assumption that a seed which does not sink is a seed that is spent, but the reality is far more nuanced than a simple sink-or-swim test. While buoyancy can be an indicator of the seed's internal condition, it is not the sole judge of its viability, and a floating seed is often just waiting for the right conditions to reveal its true potential.
The Science of Seed Buoyancy
Nasturtium seeds have evolved a specific structure that explains their initial behavior in water. The hard, round seeds possess a natural, waterproof outer shell that traps air within microscopic pockets, creating a buoyant force that keeps them afloat. This air-trapping mechanism is a standard feature of many garden seeds and is not inherently a sign of decay. The goal of the floating test is not merely to check if the seed sinks, but to determine if that air pocket is stable or if the internal architecture of the seed has broken down.
Why Seeds Float: Air vs. Decay
To understand if a floating nasturtium seed is bad, you must look past the surface and examine the seed itself. A healthy, mature seed will often float because of its design, but it will feel firm and heavy in your hand. Conversely, a seed that has gone bad due to rot or dehydration will feel lightweight, soft, or spongy. If you press a floating seed between your fingernails and it feels brittle or crumbles, the cellular structure has failed, and it is unlikely to sprout. The float test is most effective when you squeeze the seed; buoyancy combined with resilience indicates a living seed, while buoyancy combined with fragility indicates a lost cause.
Environmental Factors and False Positives
Sometimes, the reason a nasturtium seed floats has nothing to do with its viability and everything to do with the environment in which the test is conducted. Water temperature and salinity can dramatically affect buoyancy. Cold water is denser, which may cause even healthy seeds to float, while warm water might cause marginal seeds to sink temporarily. Furthermore, if the seed recently encountered moisture, a thin layer of biofilm or soap residue on the seed coat can create surface tension that keeps it afloat. Always ensure you are using room-temperature, fresh water for your test to eliminate these variables.
The Germination Test: The True Verdict
The most reliable way to answer the question of a floating nasturtium seed is to conduct a controlled germination test rather than relying solely on the float test. Take a paper towel, moisten it until it is damp but not dripping, and place the floating seeds on the surface. Sandwich them with another damp paper towel inside a plastic bag, and store the bag in a warm, dark location. Check the bag every few days. If a seed swells, cracks open, and develops a rootlet within one to two weeks, it is very much alive. This method bypasses the ambiguity of buoyancy and gives you direct evidence of metabolic activity.
When you examine the floating seeds post-germination test, you will likely notice a distinct pattern. Seeds that were hollow, shriveled, or discolored will remain stubbornly on the surface and show no signs of growth. These are the seeds that are definitively bad. Meanwhile, seeds that were healthy but simply trapped air will eventually absorb water, become denser, and sink as they germinate. At this point, they are no longer floating because they are busy transforming into a new plant.
Best Practices for Sowing
Whether your seeds float or sink, the method of planting plays a crucial role in success. Nasturtiums dislike being transplanted and prefer to be sown directly into their final growing position. If you started them indoors for an early jump, ensure the pots are deep enough to accommodate their long taproot, which seeks depth just as the shoot seeks height. Plant the seed approximately half an inch to an inch deep in well-draining soil; burying a floating seed too deeply can exhaust its energy reserves before it reaches the surface.
Ultimately, the question "if nasturtium seeds float are they bad" is answered not by the water, but by the seed's physical integrity and your patience. Treat the float test as a quick filter to remove obviously rotten seeds, but rely on the damp paper towel method for confidence. With a little time and attention, you will find that many of those floating seeds are merely holding their breath, waiting for the moment to dive in and grow.
