91Èȱ¬

Global Warming? Huh! Let’s face a couple of incontrovertible facts:

• We are an off-shore island.
• We have therefore a climate – a lack of extremes, plenty of moisture all year round but unpredictable because of the all-pervading influence of the sea

Some are sceptical about but I think most people would sign up to the fact that something is happening. Until last winter (09/10) and the present one to date it was being argued that winters would be milder but wetter. Gardeners would be worse off because milder winters would lead to less winterkill of damaging organisms. Is this just a blip on last year's blip?

Evidence that winters are getting milder in some areas has been shown in a serious way, and affecting food production. Here is one example.

A very high percentage of the blackcurrant varieties; now grown in Britain for commercial fruit production, were bred at the ; they carry the ‘Ben’ prefix. To be technical, all temperate fruits – apples, pears, plums, soft fruit must experience a period of low temperature to complete their annual physiological life cycle. It is referred to as the ‘’ and will vary from one fruit species to another and indeed one cultivar to another.

The use of the word ‘chilling’ may be slightly misleading. When I worked in this area of endeavour we called them units of ‘coolth’ (as opposed to warmth!) The plants collect these low temperature ‘units’ cumulatively, they ‘bank’ the low temp degrees, which must then add up to a given figure if the cycle is to be completed normally.. For example, in the dormant season, the blackcurrant variety Ben Lomond must collect 2000 hrs below 7.2 °C and if they don’t get them, problems will arise.Ìý It has been recorded that commercial plantations of some of these varieties in the south of England have reported erratic bud break, leading to a reduction in fruit quality. This is one of the classic symptoms of not reaching the chill totals. In layman’s terms, the winters have been too mild.

Go to the other side of the globe and you find that New Zealand varieties need accumulate a much lower dose of cold units (1200hrs or thereby).Ìý Work is therefore going on to breed new varieties with all the excellent qualities of the existing cultivars but with a lesser requirement for units of coolth.

Interestingly enough, climate change or not:

• We are still the same distance from the equator. So? As we know, that controls our day length patternÌý - short days in winter and long days in summer and that affects flowering patterns.
• We remain the same distance form the sun so the light intensity stays the same - that affects flowering too.
• More ‘dimming’ is forecast and that may lead to long periods of lower light intensity, which will seriously affect flowering of some plants.

In other words, although conditions may become warmer and wetter, we don’t get a complete package of changes to growing conditions because our global location is fixed.Ìý How will our plants re-act?Ìý Will gardens look different in 50 years time?

Have you noticed any climate related changes in your garden?

Jim McColl presents 91Èȱ¬ Scotland's the .