When compared with previous years, some vegetables had to be sown twice, some ran to seed early while some were very late in producing a useful harvest - despite adequate water, mulching and tender care. So what has changed?
While some are yet to be convinced, many aspects of the local climate appear to have changed in line with the more widespread impacts of 'global warming'. Windbreaks reduce moisture stress but two other factors of direct relevance to plant growth are temperature stress and sunlight intensity.
Mulching has the effect of moderating soil temperatures and protecting the roots. Above-ground parts of plants, stems and foliage, experience what I term 'temperature stress', the difference between overnight minimum and daytime maximum. Daily observations at Braidwood show that this difference has been increasing in each of the months September to January over the last 23 years.
Minimum overnight temperatures and incidence of frost were close to average in each of the last six months while maximum temperatures were about two degrees above average. The temperature stress in each of those months was well above average and also greater than the 23-year upward trend.
The intensity of sunlight has increased in recent years. Globally, efforts to reduce airborne pollution have subtly had the effect of cleaning up the atmosphere. This removal of 'global dimming' is very apparent in measurements of evaporation around the world as well as here in Braidwood.
It is noticeable on exposed skin that the sun has more 'sting' in it these days. Plants are probably experiencing the same effect - more intense sunlight in the middle of the day in addition to increased temperature stress. Grasses visibly benefit from dappled shading by trees.
Shade cloth could offer a solution - reducing the intensity of direct sun and moderating the maximum temperatures experienced by plants. Commercial vegetable growers at Griffith and Cobram use acres of it, strung high to be clear of machinery. Gardens could be progressively 'roofed' in the same way.
The impacts of global climate change are clearly evident in the measured effects at Braidwood over many years. The difficulties in backyard vegetable growing are a symptom of those changes. The trends are distinct and are not likely to go away in the near future. The necessity is to adapt to the changes and shade cloth over vegetables could be a step in the right direction.
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