It is not a good idea to grow potatoes in the same place every year. Potatoes are great for clearing the ground of perennial weeds because they loosen up the soil and grab all the nutrients for themselves. if you have to leave the plot for a while allowing heavy weed growth as you did, it would have been better to just hoe the surface to stop the weeds building up. I'm sure you will get lots of advice on crop rotation from other members but what you grow depends on what you like to eat. If you use the link below the method is described very well on a video. The chap explains how different crops affect the soil and how much space is required to grow eg 100 carrots, they will grow in a square metre. I used crop rotation in a four year cycle. When I cut down on the type of veg I grew I used to leave plot four to recover. When I stopped growing veg. I missed my fresh potatoes so I grew them in big pots instead. https://www.myallotmentgarden.co.uk/how-to-decide-on-crop-rotation/

As Bamboo says, crop rotation is preferable to growing one crop in the same place year-after-year.
However, what you have described above as your treatment of this bed just now is good. If the weeds have grown so quickly and thickly they will be annuals and you have treated them as a green manure crop. These weeds will now rot down over winter and nurish the soil.

YOu might consider dividing your plot next year. There's not much room to have three sections but you could manage two perhaps? It would mean fewer potatoes but you'd have other stuff as well. You might even have a year of growing spuds in bags so you could use the plots in your rotation plan? You could get the nitrogen fixers in by growing Aquadulce broad beans which will stand over the winter (especially with a bit of winter protection from a tunnel cloche) And they'd be finished in time to plant something else in the same space.

I agree with above. Crop rotation is key to success. The plot needs time to recover & replenish. Weeds actually help in restoring vital nutrients & prevent soil erosion.

'If it weren’t for weeds, the world would have lost more topsoil than it has to date, and humankind might have suffered mass starvation by now. Why? Because the plants we call weeds do a vital job in ecosystems: they quickly establish in, protect, and restore soil that has been left exposed by natural and human-caused disturbances.'

Full article:
https://articles.extension.org/pages/18529/an-ecological-understanding-of-weeds

Thanks very much guys, I never thought about using the hoe - I don’t remember the last time I did ! But had I used the hoe would I then have to chuck a great big pile of weeds into the waste bin to be got rid of ? I will definately grow my spuds elsewhere next time. I now have just the spot.
The reason why I’ve grown them there is because my soil there is awful dark, heavy clay stuff and I thought this veg might help - I know I still have a lot to learn. So what to do about it, and what to grow there next year ?

You can leave the weeds to rot down where they are as long as they haven't set seed. (unless they are really mature tall ones...) Or if you dig them in they will help to improve the soil texture. Can't remember whether you have a lawn but if you do you can spread a really thick layer of mowings on the soil in the autumn and they will have gone a fair way to having rotted by spring, when you can dig them in. If possible loss of nitrogen bothers you you can always add some general fertiliser before planting. I was warned off doing this but did it anyway and it made a big improvement.

Hi Sue, have just spread a thick layer of last year’s leaf mould on my raised beds, but have no leaf mowings left for the lawn, but will certainly remember this for next year.

Great stuff Hank. It should prevent weed germination over the winter as a bonus.

Looking into the 'Lasagne Method' might be useful Hank. Basically it goes with 'no dig' growing. You put down a layer of cardboard then cover in compost etc. then more cardboard & so on. A final covering of black plastic keeps down weeds, helps heat from composting veg matter & Spring warming from the sun

That looks good D, but does the cardboard eventually rot or do I have to remove it at some stage ? And how many layers of each ? I’ll try anything once.

Really wet cardboard will just turn to mush. You'll have to do some reading to work out if it's good for you but basically it's a bit like spreading a compost heap over your growing area.
Good compost is made from brown materials & green materials in layers. Cardboard = brown, grass cuttings = green. Stake some black plastic over the top & it should be beneficial! It's surprising how much your worm population will help over Winter too

Thanks D, have just the spot to try that.