This is a photgraph of a sunflower, taken today in my garden. It is of the Golden Sunset variety that has multiple red and orange flowerheads. I strongly recommend it - it is truly spectacular. (I don't even remember planting it, so it may be a volunteer from last year) However the really remarkable thing about it is that 'today' is only two weeks away from the winter solstice! - what is a sunflower doing thriving in the middle of winter? And I mean thriving - not just hanging on and slowly dying like the once mighty tomato plant next to it - it really is a strong and healthy plant, heading fast towards flowering. What is going on?
This post is not so much about climate change, as climate variability, and how plants (and gardeners) respond to it.
What I would like to do is to respond to the weather as it turns out. My interest is not so much in predicting the weather, although that is a noble and immensely useful cause. No - what I am interested in understanding the variability in temperature , rainfall, wind, humidity etc in my local area and having gardening strategies ready to respond no matter whow it turns out. In the last few years I have tried to optimise my gardening techniques to drought, but was caught out this year when it turned out to be much cooler and wetter than expected.
Fortunately we have an excellant resource in the Australian Bureau of Meteorology (www.bom.gov.au). It is a truly great site with a huge amounts of data, explanations and learning opportunities. I am particularly interested in the historical weather data for my closest weather station (Katoomba). Although Katoomba is about 200m higher up than where I live, it gives my approximate situation. The following graph shows what minimum daily temperatures are like in the months January to June.
What this shows is the steady gradual decline of minimum (overnight) temperatures as the seasons progress from Autumn to Winter. Note that they do vary quite a bit from day to day and from year to year - overall 2007 was quite a bit warmer than 2008. The deciles can be read as follows : if all the temperatures for the same day of the year, over 100 years were listed, then 90 of them would be above the 'decile 1' temperature and 90 would be below the decile 9 value. In other words, on any given day you have a 1 in 10 chance of the temperature going below decile 1 or above decile 9. Its all still very approximate, and dependant on what is going on with the weather at the time (I found the descriptions of ElNino and La Nina on the BOM site very useful). Interestingly, the same graph for the other half of the year shows a much greater variability - but thats another story
So what does this mean for the plants? It seems clear that despite my previous feelings that sunflowers and tomatoes were both 'summer' plants, in actual fact sunflowers can thrive in quite low temperatures, provided there is no heavy frost. This year they have benefitted from the increased rainfall and will keep going probably for another couple of weeks. Tomato plants on the other hand go into terminal decline when the minimum temperatures stay under about 10C for more than a few days - even though maximum daily temperatures can be above 15C. They need warmth!
So what matters is choosing the plant types - and the varieties within those types, to suit our local conditions. For several years now we have been researching which tomato varieties do best in our relatively short and variable growing season. At our market stall in Spring we sell over 15 varieties but emphasise prolific growth habits and small fruit which can ripen more quickly.
Beyond that - enhancing early season growth and late season survival for vulnerable types with such techniques as microclimates, cloches and emergency frost protection. I am currently re-discovering greenhouse technology - its not as easy as I thought though - but that's another story. Examining local climate data can be a useful way to know when you might need to start deploying these various tactics, and what your limits are. You may be able to stop frost, but not temperatures reaching zero degrees - but then that is all many plants need.
We already have weather that varies greatly - between days, weeks, seasons and years. Predictions are that this will increase with the effects of climate change - so we had better get used to dealing with the variability of temperature, rainfall, heat and wind extremes if we want to 'eat local'. We need to share local experience - weather memories, data, plant types, gardening techniques, tips, sucesses and failures.
I will post a photo of the sunflower if it ever makes it!
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