While many places around the world have laws in place where businesses and householders must not place recyclable materials in regular trash, here's a first (I think) - a compulsory composting law.

On Tuesday, San Francisco Mayor Gavin Newsom implemented the USA's first mandatory composting law in order to meet a zero waste goal for the city by 2020.

San Francisco also had an interim goal of keeping 75% of recyclables out of landfill and is currently at 72% - a great achievement.

A waste-stream analysis conducted found that about two thirds of the garbage in San Francisco, about a half million tons annually, could be recycled or turned to compost. By capturing the compostable portion, the city would be be recycling 90 percent of its waste. That's not only good for the environment, but good for the economy in terms of new jobs.

The compost the city generates from collections is highly sought after by farms and vineyards across the Bay Area. It's termed "black gold" and unlike the fossil fuel version it's certainly far more environmentally friendly.

Newsom pointed out that food scraps in landfill are usually in an oxygen starved environment. This generates large quantities of methane gas, another greenhouse gas that is many times more potent than carbon dioxide in terms of its heat trapping potential.

It's a brave move by San Francisco, and a fantastic one at that. It's something we should all be doing. We recycle, compost and use a worm farm. The latter two cut down the waste we can't put into a recycle bin by a further third - and this waste is great for the garden!

Pick up some composting tips.