Do viable seeds sink or float?
Written by
Paul Reynolds
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Understanding seed buoyancy is crucial for determining viability through simple water tests. Most viable seeds sink in water because they have dense, solid interiors. Non-viable seeds have hollow cavities or decayed tissue and usually float. This, of course, provides an excellent and quick check before planting.
Not all floating seeds are dead. Seeds of corn frequently float, despite being good, in their natural air pockets. Sunflower seeds may float if their shells have a light air trapped in them. I had discarded floating corn seeds before, and afterward, they sprouted in a compost pile. Always check the results of water tests on seeds with germination tests.
The seed water test is best suited for larger seeds that are heavier, such as beans, peas, and squash types. Do not use this test with small seeds such as carrots or lettuce, where size affects the buoyancy. Use the germination test for these seeds. The water should be at room temperature, about 68-77 degrees F (20-25 degrees C), for best results.
Sinking Seeds
- Likely viability: High probability of germination
- Common types: Beans, peas, squash, melons
- Action: Proceed with planting or further testing
- Exception: Very old seeds may sink despite low viability
Floating Seeds
- Likely viability: Generally low but not absolute
- Common types: Corn, sunflower, hollow-seeded varieties
- Action: Verify with germination test before discarding
- Note: Some viable seeds float due to air pockets
It is essential to perform water tests correctly to obtain accurate results. The water should be at room temperature and in a clear container. Add the seeds and wait 15 minutes before testing the buoyancy. Then gently stir the water to release the air bubbles from the surface of the seeds. After 15 minutes have elapsed, remove all seeds that sink immediately in the water but later float to the surface.
Combine other methods with water testing to ensure accurate results. Germination tests give you positive evidence that the seeds sprouted. Tetrazolium tests indicate whether there is cellular activity. Water tests alone are only indicative. By using various means to assess seeds, you do not dispose of those seeds that may be good, based solely on the flotation practice.
Read the full article: Seed Viability Test Guide: Ensure Your Seeds Grow
