An old salt I spoke to recently recommended these additions to your house plant soil for healthy plant growth. Feed house plants with melted snow (in season obviously!) It is rich in minerals. Or use water in which eggs have been boiled. Or use flat soda water. Or use the water in which fish has been frozen. I would recommend you do not use a combination of all of these ideas as you might get a strange chemical reaction!
Feed ferns with leftover weak tea or bury a weak teabag in the soil beside the roots. The other idea that is said to be beneficial to plants is to feed them with a teaspoon of caster sugar or olive oil every three months.