I just soaked some castor bean seed (24 hrs.). Some have sank to the bottom of the jar and some are still floatig. Is this an indication of viability? If so which is which?
How do you tell viable soaked bean seed
The rule of thumb is that the ones that float aren't viable, but I've planted floaters before and had them sprout so I'd try them anyway.
Actually, it is not a rule of thumb about floating seeds, but more an old wives tale. Yes it is true that some seeds that float in water may not be viable, but it is equally true that some seeds that float will be viable (and the same is true for seeds that sink). This will vary among species and floating seeds may mean nothing more than there is a small air bubble adhering to the seed or there is air trapped under the seed coat.
The thing you should be looking for when soaking seeds (presumably after scratching or nicking the seed coat) is if the seeds have imbibed water and increased in size. Those that haven't may need more time in the water or may need more scarification. However, just because a seed has imbibed water doesn't mean that it is viable, it just means it absorbed water.