You already found your source. Watercress is incredibly easy to grow from cuttings. Just stick it in a glass of water or in very moist soil, and roots start to grow in under a week. Hopefully, Whole Foods will still have it when you go back.

Is it safe to assume the grocery store 'watercress' is true watercress? I bought some a week ago, placed it in the top of the waterfall as well sticking pieces out from rocks (with the stems in the water) and it definitely rooted fast, within 6 days. The price was right. Tonight I saw three Blue Jays splashing around in the top of the waterfall among the watercress, though I assume all they were after was a drink of water and a bath (the watercress didn't look at all harmed). I've never noticed so many birds visiting the pond since I redid my waterfall. Glen

Hi brodpro. The short answer is toss the pot along with the potting soil and get the watercress into the water where it will root & multiply and function as a filter. Watercress can be persnickety but it's easy to grow given the right conditions. It does best in cool temp moving water so a stream is ideal. I just tuck sprigs under rocks where water is flowing & leave it alone. It dies back in the intense summer heat here but reappears when cooler weather approaches and is back every spring. Btw, I buy mine in the produce dept of the grocery store for a buck & some change. It will root almost overnight once in the pond. I also toss a few sprigs in my skippy & it is totally obscured in short order. It fares better there as the skippy is shaded during the heat of the summer. No room for a floating island in my pond (actually three puddles that flow together) so I had to get creative. I took one of those rectangular foam pads meant for kneeling in the garden, drilled it full of holes & slipped a sprig of watercress in each hole. I anchored my tiny makeshift island at the base of my waterfall (a delusion of grandeur, more like a cascade). The foam kneepad was soon hidden by the watercress. Been doing this for years with excellent results. Can't beat a successful project for under $3 On the other hand, water hyacinth flat out refuses to perform for me yet I stubbornly continue to buy it year after year. It will live - and bloom even! - but it will.not.multiply. Makes me crazy to see ponders here tossing it by the bucket load on the compost pile. Good luck with your watercress. It's mid-spring for you isn't it? blessings, ~digger

The toxic algae does not appear to grow in colder water. Most of it seen here is in water in full sun, close to the surface where the sun can raise the water temperature. What we have seen here is if the water has higher than normal levels of Phosphorus and Nitrites and a lot of sunlight the toxic algae will grow, but if the water is shaded with little sunlight there will be no growth. Whether algae growing near a mineral spring would have more nutrients depends on too many other factors to say for sure.