I always suspect too much water when SWCs are involved. I see some black on your tomato stem that looks like a disease, but I've seen the same thing on plants that drowned. I've found one of the best ways to determine moisture level in a dual bucket SWC is to lift up the upper bucket and feel the weight. It's somewhat subjective, but if it feels heavy for its' size, then it's likely too wet. If it feels unexpectedly light, it's too dry (and in the middle is just about right). A 5 gallon bucket is very deep, so you can't judge the total moisture level by just the top 4 inches of mix. Did you recently have a heavy rain/s? If so, your mulch cover may have actually funneled too much water into the crown of the plant, the smaller plants would be more susceptible. Are your drain holes low enough? HomeDepot buckets vary in design depending upon region, so if you used the GB measurements you need to double check and make certain that the drain hole is at least 1/2 inch below the bottom of the soil bucket. Make sure that buckets are relatively level and if not, rotate the drain hole down hill. Lift out the soil bucket and look at your wicking cups. Make certain that they didn't get crushed or split, allowing too much water in. What size cups did you use? The cucumbers may not do as well in Raybo's 3:2:1 mix as tomatoes and peppers. I have a Zucchini that's doing gangbusters in straight Sta-Green potting mix, and another that's not doing that well in the same mix my tomatoes love (3 parts Dr. Earth potting soil, 2 parts Fafard Aged Pine Bark, 1 Part Pearlite). My point is that it's possible that there are different things wrong with the cucumber vs. the tomatoes/peppers. You can't rule out water problems just because one pepper plant died and one survived in the same container. One plant could have received too much water at the crown (mulch cover funnel), the other could have been large enough to withstand deluge, or could have been better adapted to the wet conditions. What brand potting mix and pine bark did you use?

Perhaps the potting mix dried out.

Ahoy matey seysonn has the general idea but he's confused his equinox with solstice, so here is the definitive information you can engineer perfectly a Melbourne VIC garden with: Here's your best info on the planet: Date, Direction, Maximum Solar Elevation, Mid-Day Shadow factor Nov 1 due North, 67 degrees, 0.42 Dec 1 due North, 74 degrees, 0.29 Jan 1 due North, 75 degrees, 0.27 Feb 1 due North, 69 degrees, 0.38 Mar 1 due North, 60 degrees, 0.58 Apr 1 due North, 48 degrees, 0.90 May 1 due North, 37 degrees, 1.32 Jun 1 due North, 30 degrees, 1.73 An example/notes: On Summer Solstice 10:03 am AEDT December 22, 2014, the Sun will reach its maximum elevation, 75.634 degrees @ 13:18 AEDT. Your season winds down around May. Example: On May 1st, the mid-day Sun is due north at 37 degrees elevation. That means a plant at mid-day casts a shadow 1.32 times its height, blocking light due south of it along the ground ... e.g. a 2 meter plant will cast a 2.64 meter shadow along the ground, which is its shortest shadow of the day since this is the mid-day Sun I'm giving you ... the astronomical "high noon". Clear skies oops, wrong forum... happy gardening ;-) PC This post was edited by PupillaCharites on Mon, Nov 3, 14 at 16:54

A familiar echo from Dave above.. Transplanted plants often "pout" a little until they settle in lol.. Be sure to water them well immediately after transplanting, and it doesn't hurt to give them a few days of shade to stretch their legs a bit. Container soil must drain readily.. You'd be better off purchasing something like Promix, Sunshine mix, or making a mixture of your own. A simple, cheap and effective mix would consist of something like compost, triple ground hardwood bark and pea gravel/silica at equal parts. You'd want to add a dry fertilizer (GardenTone for example) at the time of mixing if not using a soluble product throughout the season.