Most gardeners don’t need a Biology GCSE to know plants are partial to a bit of water, light and CO2. Together they make up the key ingredients for photosynthesis, which in turn will fuel your plants’ growth and flowering. If your plants are short of water or light, it’s a simple task to change the pump settings or adjust the lighting rig in your hydroponics setup. But what if your plants were screaming out for CO2 (and make no mistake, like any good alcoholic with an offer of a drink, your plants are not going to turn down more CO2)? Would you know how to respond to your plants begging “feed me, Seymour”? Prince Charles was probably onto something with his habit of talking to his plants – there are 40,000 ppm of carbon dioxide contained within each exhaled breath. But not everybody has his gift for waffling interminably about modern architecture and Patagonian Toothfish.