Last year's lockdown was all about sourdough baking, banana bread and garden focaccia, but it seems this time around there is a new lockdown hobby in town, and this one involves coffee grounds.

Often discarded immediately after use, coffee grounds are too good to be just dumped in the bin. Countless people appear to have come to the same conclusion and are putting their coffee leftovers to better use with the help of mushroom spores ordered online.

Gardening experts have long spoken of the benefits of coffee grounds as fertilizer or pesticide, but only now during the COVID-19 pandemic is their use in growing mushrooms becoming common knowledge.

Photos of homegrown mushrooms are, well, mushrooming on social media. What was previously more of a niche hobby is fast becoming the latest lockdown food trend after sourdough bread and homemade pasta. Meanwhile, gardening and DIY magazines have been busy giving tips.

For anyone keen to set up their own home mushroom farm, here's how it works: You order a ready-to-use mushroom packet online and can then grow the mushrooms directly from the bag using the grounds left over from your espresso or filter coffee.

Cultivators essentially only need to sprinkle some of the grains of mushroom spores onto their grounds and some lime to provide the necessary calcium.

Experts say proper hygiene is important, especially for the home kits with coffee grounds, as you don't want the wrong kinds of fungus, in other words, mold, growing on the old coffee.

Ralph Haydl, from the city of Nuremberg in Germany, said he has been selling mushroom kits for a few years now with which people can grow particularly beautiful kinds like golden and pink oyster mushrooms. During the pandemic, orders increased significantly, he noted.

Stefan Hawlik, another seller of mushrooms for home cultivation, reported the same trend. For several years now, he said, his company's turnover has been growing strongly – in 2020, even more so than before.

"Corona has accelerated the whole thing," Hawlik said, forecasting even more widespread cultivation at home in the coming years.

Those of us who throw coffee grounds away on a daily basis should know that mushrooms aren't the only way to make use of them.

A sprinkling in your potting soil should keep pests away and even ward off snails. The same applies to moles. Earthworms, on the other hand, are lured to compost heaps by the coffee grounds where they help the composting process.

Coffee is also a great fertilizer. It can be mixed directly into the soil or spread on the flowerbed. Or it can be added to compost. There it rots with other green waste to create valuable fertilizer and soil.