Just wondering, when it comes to growing fruit & veggies, what's your secret ingredient?

My friend has this amazing orange tree, turns out they put their coffee grounds around it.

I'm having problems this year with the tomatoes - which are doing pretty much nothing - and i've read to add epsom salts - apparently this is a real old timers solution and something to do with the mineral magnesium.

Also, my pumpkins are putting on lots of leafy growth but very slow with the flowers...is there something I could feed it to move this along? I've realised belatedly after fertilising it that I probably should've given it rose food instead of normal fertiliser.

So, what's your secret ingredient?