In fall of 2011 I built our slug moat to protect nursery pots from slugs while providing rainwater catchment and other typical aquatic benefits. A few months later, to prepare for spring and make the most of the contraption, I added a hoophouse over the nursery table to provide a warmer, protected microclimate for the plants, without interfering with the use of the pond as an irrigation source.
I wanted ducks to use the pond, but knew that with unrestricted access they would trash such a tiny area, destroying all plants and fish and filling the pond with poop and stirred up muck. To exclude ducks from enough of the pond to allow sheltering of fish and growth of poop-filtering cattails, I put a fence across the middle of the pond and around the excluded perimeter. Ducks could still be allowed into the protected area periodically, under close supervision.
I constructed a little ramp to make it easier for the ducks to get in and of the water.
Using thin plastic which had wrapped our lumber deliveries, I constructed a skirting sandwiched onto the table sides and posts with lathe and hanging to the water below. I hoped this would create a lower seal preventing air from coming up into the nursery table.
Next, I built a ventable upper enclosure for the plants from clear vapor barrier plastic left over from the house project. I created the end "wall" closest to the house by rolling a piece of lathe into a short piece of plastic, clamping it closed with three strong binder clips. I secured the lower half of this plastic to the vertical posts with more lathe, and tacked a couple of nails into the posts to allow the wall to be "hung" up for closure, or unhooked from the nails to half-open that end of the hoop house.
Since I didn't have posts to work with at the far end of the table, I used a single large piece of plastic for the rest of the hoop house, supported by plastic hoops screwed to the sides of the table, and draping down as the far wall. I used more binder clips to seal the junction between the large piece of plastic and the end wall, unclipping as necessary to move the sheets for ventilation.
I secured the sides by creating a small gap between the existing pallets on top and new wood I attached to the table sides just below. Tucking the plastic into the gap and wedging in some lathe created a strong seal, while allowing easy access or ventilation of the sides by pulling out the lathe.
On the whole, it worked. It definitely created a warmer microclimate and allowed faster early spring growth of the plants. Using all scrap materials, it had a distinctly amateur look to it, but was fairly easy to use for ventilating and accessing plants. I'm especially pleased with the side attachments of wedged lathe, which worked surprisingly well.
Despite lathe sandwiching it to the posts as low as possible, the lowest part of the skirting, pushed outwards by the concrete pier blocks, tended to blow around, failing to make a reliable seal. Often the skirting got stuck on the perimeter fence, potentially negating the slug-proofing function of the slug moat. The plastic scrap I used was just barely long enough to reach the water surface; with more material to work with I could have wrapped the bottom with some weights to ensure a straight drop to the pond.
The cross fence within the pond was of very flimsy construction and even flimsier attachment. A fence could have been secured to two of the table legs and anchored against their concrete piers stacked in the water below, but the placement of the table within the pond didn't make sense for that. It would have created either too tiny a pond for the ducks to use, or too small an area for plants to grow without duck disturbance.
The perimeter fencing, secured very loosely with metal stakes salvaged from political yard signs, also failed to inspire confidence. Neither the perimeter nor the internal fence were tested long-term against inquisitive ducks, and I suspect both would have required some adjustment and fiddling.
The binder clips came loose easily from slippery plastic, both where I wrapped lathe into the plastic to create the end wall and especially where I tried to clip the two upper sheets together. Again, I was using pieces just barely long enough to meet, so any significant wind put a lot of force on the joints. Slightly longer pieces with more overlap and slack would have helped. Ultimately the system needed a better connector - perhaps snap-on grommets.