Tomato first-timer - help!
I should start by saying that I’m very new to all this, so apologies in advance if any of these questions seem silly!
I started some 'Moneymaker' tomatoes from seed in a propagator about 5 weeks ago (around 7th March). The seedlings sprung up in a week or so, and ever since then it’s been an exciting - if slightly anxiety-inducing - month of daily care and attention!
When they outgrew the propagator and had grown two sets of true leaves, I transferred them into 9cm tall pots with all-purpose compost in. After a couple more weeks they’ve now started to outgrow those (roots poking out the bottom, now about 30cm tall with pencil thickness stem), so I’ve started hardening them off by putting them all outside for a few hours over the last 5 days, and I have repotted some into much larger pots. These ones in larger pots will sit on our balcony, and then I'm planning on replanting my remaining ones (in the photos attached) in the next day or two into a greenhouse that’s prepared at our allotment plot, with little beds handily all around the edge of the inside of the greenhouse.
I have started to notice that the bottoms of the stems are turning purple, the veins are purple, and the bottom leaves are starting to look purple both underneath, and on top around the edges.
I’ve read a lot about potassium deficiencies, cold temperatures, small pots, all sorts, and I don't know where to begin!
So.. is this something I need to worry about? Or is it likely the tomatoes will sort themselves out once they’re in their bigger pots/bigger growing space in the greenhouse?
Thanks in advance everyone!! Chris