I have bought these for years and never had a flower off them yet. You dont need more than a few plants as they reproduce quickly, same as the water lettuce (nice plant but also not hardy). I have tried to keep them over winter in a bucket in the shed but failed miserably, might be worth you having a go though. All the ones in the pond seem to be rotting come spring so have to buy new. I would recommend the water hawthorne though, that is hardy, long floating strappy leaves and strong scented flowers (white).