Coriander

I have more luck with confetti coriander and plant a new 10 litre pot every month between last to first frost.  Could probably eat more though!
I can't grow spinach.  Chard, beet spinach, salad leaves,pak choi all do well but spinach dies within hours of sprouting!

If you've got a slug problem I'd treat that first before tying again, you could use something environmentally friendly such as nematodes or the eco-friendly slug pellets.   I'm not sure that coriander likes being moved/transplanted, at least mine doesn't. So I'd sow it direct where you want it to grow.

I let mine grow at random across the veg plot; each year I let some plants go to seed, and once they're dry I just throw the seeds across the plot. Plants pop up wherever, and I just let them grow amongst the other veg, we always have some somewhere. I suppose the slugs and greenfly can't find all my plants at once!  Happy to send you some of my spare seeds if you PM me.

G&R

I have been very successful at growing over winter in a conservatory. They grow slow but never go to seed. If you grow enough then you cut them down a bit or cut of some of the stalks so you have continuous supply through out the winter. May work in a greenhouse??