Actually, watercress is extremely SIMPLE to grow. You can grow from seed (most catalogs and larger seed racks have it) or you can plant the sprigs from the grocery store. It does NOT need standing water, just consistently moist soil. If it does get flooded or submerged, that's ok, too. Easiest way to do it is just to get a large container with no drainage, something like a storage bin, fill it most of the way to the rim with rich planting mix, and water until it's very wet but not submerged or floating. Surface sow the seeds, then dust with a tiny bit, no more than 1/4 inch, of mix, sand, or vermiculite. It will grow quickly, and can be harvested in about 4 to 6 weeks. Sun or shade is OK, but I found that it didn't dry out as fast in the shade, and the plant was more tender, succulent, and not as prone to being hot or bitter, when shade-grown (light shade, not deep shade). It's really an easy, easy plant to grow. Just make sure the soil NEVER dries out -- you can kill it quickly with drought, but you really can't overwater it.

Pfaf.org... " sow spring in a pot emmersed to half its depth in water. Germination should take place within a couple of weeks. Prick out seedlings into individual pots whilst they are still small and increase the depth of water gradually until they are submerged. Plant out into water in the summer. Cuttings can be taken at any time in the growing season" If doing this indoors, you may want to change the water in the holding container from time to time. And provide a fan periodically for air movement...but that's thinking out loud, I haven't grown watercress.

Marshmarigolds grow wild up here in Alberta and have successfully wintered for me both with wet and dry conditions. The watercress will come back from seed with luck even after -40 but the plant will not survive. I have it in my spillway which I keep running all winter with a stock tank heater in my pond and it stays green except when it goes below about -30 it springs right back as soon as the temp warms up above -30. I shut my pump off last winter as the spillway was leaking and the watercress was back in the spring from seed. One thing about watercress is that the roots create a massive sheet and can divert the water over the edges if you don't prune them regularly. Great for extra filtration not so much for water levels. Only thing worse that I have found for that is water mint. Water iris is also a super plant for extra filtration i find

Barbara, I have used hoop houses made of PVC pipe frames covered with 4 or 6 mm plastic to extend the harvest by growing earlier in the spring or later in the fall. You can use the same types of hoop houses to grow cold season crops all winter long if you want to. I suspect the hardest part for me would be to build one that could handle the hard north winds. If you are in town where there are other houses, other buildings like sheds, some fences and hedges, trees, etc. in close enough proximity to serve as a windblock, I think a hoophouse would be very easy to erect and maintain all winter. As Ilene mentioned, Eliot Coleman's "Four Season Harvest" is the classic book on the subject. One technique I learned from him was to use a frost blanket-type row cover on top of plants that then have further protection from a hoop house or high tunnel. That way, there are two layers of protection from the cold weather. However, Mr. Coleman, who is nothing less than a national hero to many farmers/market growers and serious hobby gardeners, has a brand new book out (April 2009) called "Winter Harvest" and even though it is primarily aimed at market growers, a serious home gardener could benefit greatly from reading it and applying his techiniques. People who've read both "Four Season Harvest" and "Winter Harvest" have stated in their reviews that basically "Winter Harvest" is an updated version of "Four Season Harvest" that includes what he's learned or changed or refined since he wrote "Four Season Harvest", so I don't know that you'd need to read both. Although, I do have to say that every word he's ever written in a book or magazine article or in any of the speeches he's given over the years is well worth reading! A couple of the most important things to remember about growing in a hoophouse or high tunnel or in short tunnels (more about them later) or cold frames is that you have to be able to open doors or vents to let heat out during the day or your plants will roast. Also, the larger the structure, the easier it is to maintain the appropriate temperature because very small structures heat up too fast and also cool down too quickly. You can use short tunnels that consist of wire or PVC hoops placed over garden rows and covered with floating row cover, plastic or both. They'll keep plants somewhat warmer, but not as well as a larger structure that has more mass. You can help increase their ability to hold heat by using a soil heating cable run down the row or plastic bottles spray-pained black and filled with water and used as solar collectors. I have used those big cat litter jugs spray-painted black as solar collectors in a hoophouse to protect early tomatoes from a late freeze with sleet and snow (and didn't lose a plant). If you use only a frost blanket type of floating row cover, I believe you pick up about 8 degrees of winter protection. With plastic, you can increase that and you can increase it a bit more with solar collectors. I haven't read "Winter Harvest" yet, but it is on my list of books to read before winter arrives. Finally, although some people have success using PVC framing, others may need to use electrical conduit as framing if they are in a high wind area or in an area where snow or sleet are likely. Another way to support a hoop house structure in those more difficult conditions is to use cattle panels as part of the support for the plastic roof. The Ardmore-based Noble Foundation has done a great deal of research into using hoophouses in agriculture. I've linked some of their data below that tells you how to errect a low tunnel. Also, you can cruise around their website or google to find their various instructions for making hoophouses (and raised beds) of different materials. Dawn Here is a link that might be useful: Nobel Foundation's Low Tunnel How-To