I compared SWC with & without plastic last year. Used a faster draining mix than you buy from Earthbox or Gardener's Supply. The SWC with plastic did better, it helped keep the top of the soil wet.
However the Earthboxes are relatively shallow, so if you use a mostly peat based mix with them. The top of the soil might keep damp without plastic. I'd try it out, if the soil top stays wet without plastic, that is probably better.
I use something similar called an Growbox and the vitamins & nutrient pack is attached on the underside of the burlap top. Without it the plants may not do as well and you would have to do the watering with feed from the top which isn't necessary with the well below.
emgardener
luv2gardengirl_yahoo_com
Related Professionals
San Juan Landscape Architects & Landscape Designers · Goodyear Landscape Contractors · East Haven Landscape Contractors · Gallatin Landscape Contractors · Pleasanton Landscape Contractors · Seven Hills Landscape Contractors · Antioch Landscape Contractors · Holliston Solar Energy Systems · Fort Washington Window Contractors · Snoqualmie Window Contractors · New Haven Fence Contractors · Olive Branch Fence Contractors · Sandy Springs Fence Contractors · Summit Fence Contractors · Woodinville Fence Contractors