I will take a shot at helping, but I will say I am not sure what your climate is exactly like so I will use temperature references.

First off, spinach does like organic matter and Nitrogen. I am not sure what polluted fertilizer is, but if that is like compost it was probably a good thing to add. I add composted manure a week or so before planting then again in Spring I topdress with it.

Spinach prefers temperatures between 5 ~ 25C. Once you start having weather above 25C ( 78 F ) consistantly it tends to look 'tired'. A few warm days followed by more cool weather, especially cool nights, will revive it.

Spinach takes quite a while to germinate, and, is inconsistant, especially if the seed is not fresh. Plan on 10 ~ 30 days for some of the seed to finally sprout. They should remain moist this whole time.

Once it is up it is very tough though and with a bit of covering ( 3 ~ 4" of leaf mulch is what I use ) it can survive overwinter as a small seedling and begin growing again in spring.

I plant SPRING spinach in October. It sprouts in November, then when the ground freezes I mulch with the leaves. I cover the leaves with chicken wire so they do not blow away. Our winters last from late November/early December through about mid March. This whole time they are covered. Our low temps get down to ( -18 ~ -23C / 0 ~ -10F ), when the temps in spring get up around 10C ( 50F ), usually mid March, I remove the chickenwire and leaves. We usually have damp rain/snow mix type weather for March and April with temps from 0 ~ 20C and the spinach loves it. ( It will survive, uncovered, down as low as -3C )

HTH and was not too wordy, maybe others that have your climate will also contribute advice.

Nam

thanks and sorry about the misspelling of pelleted.
You can blame the spellchecker and my poor eyesight for that...
I try not to actually add pollution as my secret ingredient for the most part...
No my climate is very different from yours. It is the Atlantic seaboard and so very temperate and quite wet normally
The soil I am using is ,then a mix of what I would call good loamy soil as it is a mixture of old soil and weeds that have rotted down and left for a year.I sterilize this first and then I add a bit of peat moss and , as I tried to say, some pelletted fertilizer ,most likely compacted chicken manure I suppose.
The problem I have is preventing the plants from bolting.
If I could get just one to develop into a plant without bolting after a week or 2 , then I would be able to copy and improve the procedure but with zero success I am in state of limbo.
The bolting problem I have is mainly affecting very young plants.
Once they are established I can get a decent crop but in order to do this I have to buy them in from the nursery and that is a bit annoying...

I would agree with namfon in that planting spinach in the fall is way better than a spring planting. They will still bolt but you should have a good crop to harvest before they do.

If the seedlings are bolting it sounds to me like they are too warm. I would try to make sure temps never get too high while they are seedlings.

thanks
well if I have them out in the sun (don't they need the sun?) , well watered and covered with fleece is there anything I could do in addition?
Could I cover them entirely during the hottest part of the day ? Or just move them around to a shaded area since they are in small pots and so transportable?

I had a good crop of spinach this year. Here in NH (northeastern US) I put black plastic down a few weeks before planting to help warm the soil. I planted as soon as I could, watered well and covered the bed with garden fabric (Agribon-19). I think the planting date was April 10. I thought I read somewhere that spinach was day length sensitive as well as sensitive to the heat. We still had cold nights, barely above freezing but warm days. Because this was the first bed I planted I had not gotten our compost delivery so this bed didn't get the additional manure fertilizer. The crop was decent but seed from the same packet planted on the west side of tall sugar snap peas was bigger and better. It's showing signs of bolting now but we've had some days in the high 80s F. I think this bed was planted in early May.

I also wonder how much water your spinach is getting because you use a can. My first patch is only about 4x4' but I use a sprinkler for at least 30 minutes.

This year I also got planting advice from an Almanac website that would customize depending on your USPS zip code. Don't know if it works for Ireland. See if you can find out when gardeners in your area are planting. I suspect you aren't planting early enough.
Good luck next year. I didn't water my beets enough and got almost zero germination.

I've no clue but it wouldn't hurt to scan the AHS Plant Heat Zone Map.

Lucy, do you leave the fleece on all day ? If it gets much about 15C and it is a sunny day that could be kinda warm for spinach. I would remove the fleece in the morning on any day that you're forcasted to get above 10c. Unless you are trying to protect against leaf miner or some other pests.

One more thing you could try is to ask locals and see what thay do, what varieties do they grow ?

thanks again
yes I do leave it on all day -but I don't have any better success with enviromesh which I feel doesn't afect the temperature beneath as much.
I am very surprised that anything above 10 degrees could cause a problem as I had a far higher figure in my mind.(I accept that I was only guestimating)
I think that to get a day not forecasted to rise about 10 deg. I would need to wait until the autumn or the spring.

I don't suppose moving these small containers into the shade on warm days would be advisable ,would it? That would deprive them of sunshine of course but could it be tolerable?
I am only aiming to get these plants to a large and robust enough shape to enable me to plant them out to a permanent place (where I am reasonably confident they will do well)

I would think they would grow great in an Irish winter, without any covering, directly sown...And they do need lime