Tea leaf compost is one of the most readily available and a good source of nitrogen for plants. You can use dried & used tea leaves to fertilize your houseplants. 

If you want to increase flowering in houseplants such as chrysanthemums, calla lily, etc., then use dried & crushed banana peel fertilizers.

After removing the inner membrane, wash them with water and crush them to apply to plants. They are a good source of calcium & phosphorus. 

If you boil vegetables in water, start using the same water after cooling to atmospheric temperature to fertilize your houseplants as they are full of nutrients. 

Used coffee grounds are an excellent source of nitrogen, phosphorus, potassium, magnesium, etc. Therefore, use them to boost the growth of houseplants. 

If you have an aquarium in your home, you can use the waste water of the aquarium to fertilize your indoor plants. They are rich in nitrogen & potassium. 

Take 2 to 4 handfuls of onion peel in 1 liter of water in a glass container. Leave it for 24 to 48 hours in the dark. Strain liquid & mix in equal parts of water and use it.