Hi,

On throwing some water into my monstera today there was an awful stinking smell in the whole room. Lifted the plastic inner pot up from the ceramic outer pot, it was sitting in a few inches of brown water which was absolutely stinking like rotten eggs I took the whole plant out and the soil was completely wet and heavy. The roots were coming out the bottom of the pot a bit, it probably needed repotting anyway.

I genuinely don't water the plant often, every 2-3 weeks if I remember? seems completely healthy otherwise. It's 1.5m tall with large holey leaves and more coming.
Do you think this is a simple and sad case of overwatering?

I think you need to drain the cache pot (the ceramic outer pot) everytime you water.

Yes, I consider incidences of standing water in a cache pot as a type of overwatering. But this doesn't require a label, just some attention if you can't repot right away.

If you rinse the soil well outside (warm shade) or in the shower, until it's not brown anymore, that should help get rid of the odor and freshen the anaerobic condition. After that, if the root ball will slip from the pot in a solid mass, you can let it continue to drain and get some oxygen back in the soil. Just don't let it get too cold or sunburned if you do this outside. Another option would be to brace the pot in a tilted position, with a drain hole at the lowest point, where it can continue to drain for an hour or 2.

After this activity, you should be more familiar with how heavy it feels when fully saturated so you'll know to check for water trapped in the outer pot if it's too heavy to remove every time you water.

If the soil surface felt moist when you added more water, that's a definite clue that no more water is needed at that time.

Best luck!

I agree with the thoughts above, and will just add that Monstera deliciosa is very tolerant of stagnant water, and not to worry too much.
I have rescued several that were growing in foul conditions, and once the stench was rinsed away they were fine and resumed growth.

Thank you all

I am going to re-pot in fresh soil and hopefully it takes (and put it on a tray instead of in an outer ceramic pot)

Happy to reply. : ) This is a common struggle, trying to hide a less attractive pot inside a more attractive pot without a hole. Best luck!