full disclosure i do not grow - but i do consider myself an avid gardener/nature enjoyer.
assume you’re talking about outside - i’ve heard good things about pest repellent plants to keep…more important…things safe. things like cilantro, parsley and dill are supposed to have pest repellant properties. edit to fix typos
flowers like chrysanthemums and marigolds attract ladybugs and other pest killers.
things like chives also allegedly have antifungal(?) properties.
if you’re talking not outside, i agree with shareni - cover crops are great. i buy a 1lb bag of mustard seed every year and sprinkle that shit everywhere and then let it grow/die/fertilise the soil.
venture capital / investor cash cannons