I'm trying to prove or disprove the peat tea theory, so here's the story so far:
I've always followed the advice that red tubes hate being repotted and it takes a couple of years to get them back on track. I have a couple of red tubes that were very red in the past and look faded this year. Conversely, a red tube I received bare root that was potted up in fresh peat in March has reddened up fantastically. I suspect they like being repotted every year or two, contrary to what's been written, as long as it's done during dormancy.
Here's the test subjects: flava var. atropurpurea with the 'reddish copper top' look and green tubes. This hasn't been repotted for 3 years. Next to it is a flava red tube grown in the same conditions that I received bare rooted in March. It's red from top to bottom.
Firstly I tried making tannic tea using cold water and peat in a muslin bag left overnight. I filled the tray completely with it to enable the plants to suck up the black water over a week or so. Result: no apparent improvement, despite a lot of sun during this June. Is this due to using cold water or using the tray method of watering?
Now I am trying the boiled method of making peat tea, as per the original instructions. Peat was boiled for 20 minutes, was strained and left to cool overnight. Today I have used this on the atropurpurea (watering from the top only this time). I'll repeat over the next couple of weeks and report the results.