Did you know that tea leaves are great for composting?

At Plantation, we donate our used and expired tea leaves to a food waste composting project that is part of ISF Academy's Shuyuan Sustainability Program. 

This project uses "The Rocket", an aerobic composting machine, to turn food waste from the cafeteria into compost which is then used in the school gardens.

Why tea leaves are great for composting

Tea leaves are one of the best things you can add to compost. Here's why:

1. They are rich in nitrogen, which is needed to counterbalance carbon-rich ingredients like rice. 
2. Steeped tea leaves also help boost oxygen levels in the composting process, which the microorganisms need. 

The Carbon-to-Nitrogen Composting Ratio

This ratio is the most significant factor in the composting process. A carbon-to-nitrogen (C:N) ratio of 25:1 is needed for ideal microbial activity. In other words, when composting food waste, you need nitrogen-rich ingredients to balance carbon-rich ingredients (e.g. carbohydrates) - and tea has the highest nitrogen content of all. 

So, for 1kg of rice, you'd need 40g of tea leaves to achieve the ideal C:N ratio for microorganisms to turn food waste into compost. 

The food waste composting project

This project, led by by Diana Lynne Ibarra and Shangyi Shayne Jiang, was started in 2014 as part of ISF Academy's Shuyuan Sustainability Program, with the mission to divert organic waste from landfills. 

Hong Kong produces an estimated 3,648 tonnes of food waste every day. This waste is disposed of in landfills where it generates methane, a powerful greenhouse gas driving climate change.

The Rocket turns food waste into compost via a continual aerobic process. It provides the ideal conditions for composting and microorganisms' growth by controlling aeration, moisture, and temperature.

How the composting process works:

1. Food waste is collected from the school kitchens, chopped up and spun to dry by a Dehydra.

2. A bulking agent is added to dry out the mixture and ensure it is the right consistency for the Rocket. The bulking agent used here is shredded paper.

3. The mixture is added to The Rocket together with our tea leaves.

4. Inside the Rocket, a large corkscrew structure slowly moves the food waste along. The composting happens naturally with bacteria and oxygen, with conditions inside The Rocket warming up to 65°C. The aerobic process is a lot less smelly than the anaerobic process.

5. After about 14 days, the mature compost is deposited out the end of The Rocket at room temperature and is taken up to the school gardens to be used as organic fertiliser. 

How to compost your own steeped tea leaves

If you have a composting bin at home, add your steeped tea leaves to it! (Only loose leaf tea, though - don't add tea bags to your compost bin.)

Drain them first so they are dry or slightly damp before adding them to your compost bin. They will help boost microorganisms' growth and ensure a better quality compost output at the end.