Mushrooms - are they safe for celiacs?

[TheDHhurts]

I stopped eating mushrooms post-diagnosis because I was told they were grown on hay/barley/some sort of glutenous substance, and that I would end up getting cross-contaminated.

More recently I've seen some people challenge this, saying that modern farming practices do not expose mushrooms to gluten cross-contamination.

I'd like to try mushrooms again, but I'm very cautious about introducing new foods because I'm very sensitive (I have DH, and seem to break out from minute amounts of cross-contamination). Any suggestions on how I should proceed here?

Thanks!

[Blue-Sky]

I eat mushrooms often and I don't get a reaction. I doubt that mushrooms are grown on wheat as it is well known that a lot of people are allergic to wheat. If a product contains wheat intentionally it has to be labelled. This probably makes it less likely for companies to take risks with peoples healths by using wheat. Probably the same for barely as it is not safe for Celiacs. This source says they are grown on millet. Hay is gluten free. 

https://farmingbase.com/growing-vegetables-in-greenhouses-is-more-profitable/

Also mushrooms get washed really well and I don't think they absorb nutrients from the soil but they probably wouldn't absorb the wheat itself.

[Scott Adams]

I've never heard that mushrooms could contain any gluten, even if they were grown on wheat and/or barley. If you simply wash them before use they should be gluten-free. This sounds like a similar version of an age-old myth that strawberries could contain gluten because they might use wheat straw under the plants. I don't believe that either claim would hold up to serious scrutiny.