That's really cool! Unfortunately no balcony or outdoor space here! We've done some small herb pots inside before which worked wonderfully but that's about the extend of anything we can do before we move.
I just want to say that, coming from someone who lives in an apartment building, I'm extremely jealous of your being able to grow your own food. Plus that you're growing things that are a little more out of the ordinary like the lemons and kohlrabi AND have a green house. Stellar!!
btw, how long have you had those lemons/how old are they? I've always assumed that fruit only grew on larger, older trees but the ones in your pic seem quite tiny (no offense...haha)