Dr Who I wouldn't advise anyone to plant horseradish as it can completely take over your garden.
When I was young my father was posted to a house with a garden full of the stuff.

He made gallons of horseradish sauce for the whole village, but after 4 years it was still cropping up everywhere.
Haven't come across a crab apple yet, but it could be grafted onto an existing apple if you could bring some nice fresh twigs from a John Downy owned by a friend in the UK in the winter.

John downy makes the best crab apple jelly in my experience, lovely rosy colour and delicious. I'll keep my eys open though.
BBLUX all the maize grown locally IS animal feed. I have been asking seed companies for sweetcorn, which is known as Dorra Saccarea in the seed trade apparently. They know what it is but seem bemused by the idea of anyone wanting to grow a significant amount. (Coz we'll share the seed of course.

)
Asparagus Mmmmmmm. Worth a try, but in the UK it takes three years to establish a bed - it's a blighter to keep the ground clear of weeds because it has to be hand weeded, needs heavy mulches of FYM or weedfree compost and then ................. After you take the spears the top growth is very ferny and exhuberant (making weeding difficult) I think the low humidity would dessicate the ferny top growth. It's expensive because of the labour involved in growing it in the UK. A quarter acre belonging to a neighbour in the UK supported his family! It was also his full-time job.
Jane I've seen parsnips here, very thin, thinner than a carrot. I want to try some though. Turnips are grown here, small ones about the size of a golf ball. The tops and roots are eaten raw. Not very popular it seems. Swede I haven't seen, Celeriac yes, but not often. Beetroot isn't eaten here! It's used as a garnish only. I buy lots of it though it's quite expensive as it is so good for you. It shoud be available all year, but I've only seen it in the spring. I will definitely be growing beetroot in both colours - the yellow is my favourite. I'm sure I will have to bring the yellow seed from the UK.
Mushrooms need a steady temperature and humidity, that's why they grow them in old railway tunnels. They don't need dark, when my kids were young they grew mushrooms in a bucket in the kitchen. The wild ones in our fields came at the end of the summer for a few weeks, Giant Puffballs we had all summer.
Jewel, I couldn't agree with you more. Egyptians love roses even the ones that struggle with their climate, but are totally amazed if they see a rose in full bloom in the UK.