kevokie,
Wow, we are on the same wavelength today!! Just came back from Lowes with 4 bags of their Sta-Green Potting Mix. I recalled when I used it last year that it had a larger particle sized composition than the Miracle-Gro. What I am learning now is that larger particle size media will lessen the moisture content, so will give this a try in a 'Tainer later today.
I am also going to load up a 'Tainer with the Cactus Mix to evaluate wetness although, I am a bit concerned about the sand component of the Mix. Again as above, the smaller particle size of the sand will actually cradle more water (think of walking on the beach on the shoreline, and how saturated that sand is when you dig into it). The sand might be good at draining a traditional container with top down watering, but how it will impact "bottom-up" capillary watering in a SWC is to be determined.
Regarding your suggestion of removing the plastic mulch, that is EXACTLY what started me off on my quest to "tune" the moisture content of the potting mix. I planted a pair of Big Beef some time ago and left off the moisture barrier. These two plants are the healthiest in my entire 'Tainer Farm today:
Green foliage from bottom to top. No "leggy" vines, etc. Perfectly shaped tomatoes. My other Big Beef with the moisture barrier has wilted branches at the bottom, and the fruit are heavily lobbed. The only downside of leaving the moisture barrier off (two actually) is that the 'Tainer will use more water per week due to evaporation give-off, and the fertilizer strip running around the top of the 'Tainer would not make good moisture contact to disperse throughout the 'Tainer.
I can bury the strip deeper into the potting mix as an option, but again, I would rather keep the moisture barrier and instead focus on controlling the top-to-bottom moisture within the 'Tainer by blending a combo-mix to give the desired "Moist" reading on the meter, and not just have the top 3 inches being drier.
I have also just purchased a couple of 2 cubic foot bags of Perlite to also blend in with the original Miracle-Gro potting mix. Not sure of the ratio that I should use, so it will be trial and error for a couple of iterations. Fun stuff!!
Ray
