If you’ve ever watched that classic 1970s TV series, ‘The Good Life’, you might have some idea of the work involved in attaining self-sufficiency. As funny and light-hearted as it was, ‘The Good Life’ offered many insights into the unenviable lot of the vegetable gardener. To its credit, the programme was also willing to cross the line from comedy to tragedy, occasionally playing out a poignant scenario in which the Goods (and probably some of their viewers) ended up in tears. More than once the exhaustion and stress took their toll on those affable Surbiton survivalists.
None of the thirty-or-so episodes ended with ‘secateurs at dawn’ but we still got the impression that gardening can be seriously demanding. The digging is difficult enough but the subsequent planting is time-consuming and tricky and the ongoing maintenance can overwhelm the unwary. Then there are the weeds, the weather, the wireworm and the slugs. If you’ve ever tried to grow your own groceries you might have wondered how the horticulturists make it look so easy. Well, they have at least one big advantage over Tom and Barbara: carbon dioxide (CO2) enrichment.
WHAT IS CO2 ENRICHMENT?
CO2 enrichment is now an established technique for improving the productivity of plants grown in controlled environments. It is used extensively in large-scale greenhouses for cultivating tomatoes, peppers, cucumbers and salad crops. Increasing and maintaining the levels of CO2 in an enclosed growing space is known to enhance growth in some plants; it helps them to flourish and therefore increases yield and profitability. Tests have shown that elevating the CO2 from the atmospheric level of 350ppm to 700ppm (parts per million) may boost production by up to 30%.
Plants develop and grow by a process we know as ‘photosynthesis’. This enables them to absorb CO2 and water which they convert into sugars and oxygen using energy from light. These sugars provide the nutrients required for growth, and the oxygen (a by-product) enters the atmosphere where it supports aerobic respiration (breath). We inhale this atmospheric oxygen then exhale it as carbon dioxide which is then absorbed by plants in what is known as a symbiotic relationship. Nearly all of the carbon in plant material originates from this gaseous carbon dioxide in the air.
Horticulturists and greenhouse operators have several methods of generating the CO2 required to supply an enrichment system. In a small space it may be possible to use bottled gas or dry ice, or perhaps a fermentation or decomposition system. However, each of these methods has a few disadvantages when compared to the options available in a larger space. Appropriate solutions for a larger space typically include a gas-fired water heater fuelled by propane, butane or natural gas. When burnt cleanly, these fuels generate the CO2 gas which is then distributed to plants.
Whichever method is used to produce the extra CO2 for such a system, it is essential to monitor the ambient air in order to maintain an optimum CO2 gas level. This level will vary depending on the crop, the ventilation system, the relative humidity and temperature and any plant irrigation or fertilising regimes in place. Appropriate monitoring can be provided by CO2 sensors installed at strategic locations—these can offer not only continuous real-time monitoring of the CO2 gas concentrations, but also audio-visual alarms to warn the occupants of dangerously high levels.