DIY Natural Fertilizers
This is a quick and easy way to provide extra nutrients to your plants. All of these are basically free and zero waste.
Cooking water
If you like to boil veggies before you use them and then throw away the water, dont! Not only is this cooking water nutrient rich, it also can serve as a natural dye in many cases. You can also use it to make vegetable stock:)
If none of these options are useful for you that’s okay, one last thing you may want to use it for is to water your plants!. Wait for the water to cool down and distribute among your plants. The nutrients help give roots extra boosts.
source:17 Totally Ingenious Gardening Tips
Banana peel
Soak 2-3 banana peels in about 3-4 cups of water. Cover lightly and leave for three days. DO not leave for over three days because the peels will ferment and may explode if they are in a sealed container. You may want to use gloves when distributing this potassium rich water to your plants asit can get quite smelly. It is a great and easy fertilizer! My plants love it. It is not recommended to do it more than once every 3 months.
source:18 Uses of Banana Peels : How To Use Banana Peels In Your Garden
Coffee grounds & Tea leaves
Use coffee grounds to fix nitrogen in your plants. You can sprinkle the ground over the soil then water (in some cases of high humidity just sprinkling will cause white mold, be cautious). Or bury the grounds in the top layer of soil or soak the grounds in water before straining and using the water to water your plants. 
source: Plants That Like Coffee Grounds
