[GreyScales]

Two questions if I may

There are small brown mushrooms coming up in my trough of overwintered onions. Could the fungi contaminate the onions and make them inedible/poisonous? I don't know the variety of mushroom I'm afraid.

Last year my attempts to grow normal sized courgettes in pots was a bit of a disaster, so this year I'm trying a variety specifically for containers. I've got Patio Star courgettes and I'm also giving Butterbush winter squash a go, but the one piece of information neither of them seem to specify is what size of container to use For varieties intended for containers, all the instructions I've found are for sowing in the ground.

I know bigger is better, but in a block paved garden with limited growing area; I'd appreciate the optimum size in cm/inch if possible. I'm assuming it's 30-40cm for these compact varieties?

Thank you for any assistance.

[New shoot]

The mushrooms are indications that the compost in the trough is sitting pretty wet, but I think its highly unlikely they will contaminate your onions 

As regards planters for your courgette and butternut squash, I would concentrate on getting a good deep container. 30-40cm across the top is a bit on the small side.  Maybe try going a little bigger.  If the container was twice as deep as wide, that would really help.

These are hungry, thirsty plants, so I personally would use mix multi-purpose compost and John Innes no 2 to give the growing medium more substance.  Water retaining gel would be a boon if you have it.  Then water and feed really regularly. 

We have in the past done various pots at work (garden centre) to dress up the veg plant area.  Even though we have the hose going almost non-stop over the summer, anything from the cucurbit family seems to need twice as much water as anything else 

[Headgardener22]

Slow release fertiliser in the pots would also help.

[GreyScales]

I'll certainly look into bigger containers, but as with everything for me its space space space So it may come down to having one less plant to provide the remainder the necessary container size.

Also glad to hear my onions are unlikely to poison me