You should be careful when staking a plant after it's matured. You can damage the root system that way.

You can try caging it. Can you send us a pic, so we can see what you're dealing with?

Are you over-watering them, leading to crown rot and/or root rot?

Shallow rooted plants is usually due to frequent shallow watering. Roots remain at or near the surface and the plant becomes water dependent and the roots rot. Less frequent but much deeper watering is better. More water/less often.

This is especially common with pepper plants as they prefer much less water and less frequent watering overall than many other plants. They prefer to dry out some between watering.

Planting pepper plants deeply so that much of the main stem is also buried and then providing deep water only as needed usually solves the problem.

Dave

Not overwatering for sure and no crown rot at all. They have mostly been covered in a cold frame and it is possible the roots are shallow - but other pepper plants right next to one with issue are ok. Last year plant it happened to was doing GREAT for weeks, picking peppers etc, then one day it had fallen over I thought someone bumped it but that was not the case.

also this happened over night - very quickly. Plant is now wilting, as expected.

Any chance of a picture?

Did you mulch right up to the stem?

Could you take a look at the wilted plant. Gently dig the soil away (with your fingers) at the base and see if there is any thinning of the stem in that area.

I've had that problem with tomato plants where it looked as if something had nibbled away at the stem right at the soil line, but it turned out to be a disease for which there was no cure :-( Hopefully, that is not the case with your pepper.

Linda

I did not mulch and grew from seeds all other plants are OK. I don't go around the roots and found no issues I will get a picture soon but it wilted very fast.

I am starting to think I might have bumped it and broke it off a lot of the roots but not the stem? Has anyone ever done this? it seems odd that the roots broke but not the plant?

Most pepper plants need support. If you wait until the root system is badly damaged from them falling over it is too late. The damage occurs right below the surface.

I don't know what is wrong, but It desperately needs a drink. Hopefully it isn't damaged and can take in some water.

Linda

Could be bacterial wilt

I do not think so - again happened overnight and got extremely bad right away and roots gave out - bacterial wilt does not act like this. Watering is not helping, 10% better after water.

Sorry, bacterial wilt doesn't act like what exactly? I am no expert on it, but rapid that is not helped by watering sure sounds like how it acts to me.

Me too. That is what happened to my tomato plants. All of a sudden they started wilting during the day and then reviving overnight, but after a while it was curtains for them.

Linda

I know you said you're not over watering, but Is your soil actually dry or wet down to like finger depth? I've had peppers look like that from being too wet in the clay areas of my garden, and too much water is just as bad as too little (peppers do prefer to be on the dry side). Just wondering if you've actually checked/felt for deep soil dampness/dryness.