If you believe the weathermen we are experiencing more erratic and extreme weather conditions than gardeners of a century or more ago. Although reading old records one realizes they did not exactly have an easy time of it. Back then their weather if harsh was apparently more predictable. Winters were colder, indeed frighteningly so, but the seasons were obvious with their changes allegedly more marked than now. Their summers were apparently sunnier even if on average they were not as warm as we now experience.
And therein lies one of the most common misconceptions about climate warming. Some foolish people are planning orchards of citrus and olive groves expecting to languish under the blazing sun of a Mediterranean summer. Do not be mislead- the British Isles are going to remain many hundreds of miles north of anywhere even remotely Mediterranean and the sun can just never blaze so hot at these latitudes here as down there. Secondly we are stuck on the edge of a huge great ocean and totally surrounded by cold water with no bit more than fifty odd miles from the sea. We are always going to have a cool maritime climate even though climate warming is warming it up a bit on average. But climate warming is altering our weather considerably. Or more exactly; it’s making our weather even more extreme and unpredictable. We are going to have to deal with more and longer droughts, more and fiercer gales, nastier hail, more torrential rain, and all these superimposed on less differentiated seasons.
But kitchen gardeners are already well acquainted with methods to store water, to keep off wind, hail, heavy rain and late frosts. Sure we may have to learn to protect more of our crops than now. Let’s hope it will be less but we already grow so many different sorts of crops we already have the ways to look after them.
The obvious solution to most problems brought about by climate change is to grow under some sort of cover from a cloche to a polytunnel. Growing under cover reduces hail damage, rain splatter, rain erosion, some frost and of course can extend the growing season. Cover not only prevents gale damage but reduces wind which is very important as few crops grow well in winds of more than four or five miles per hour. We may well have to use hedges and wind permeable barriers for outdoor crops anyway. But apart from the cost and practicality of growing more crops under cover it may not be as easy as first thought.
One of the deceptions of climate warming is that it deals with two very different changes. The first is with extremes- we have certainly had some of the hottest, driest, wettest, windiest weather on record. But accurate records do not go back far and to be sure if you look at the old reports there certainly seemed to be plenty of extreme weather in times past. The other change is in the averages. Now there are lies, damned lies and statistics. On average people have approximately one testes and one ovary each. On average you would be comfortable with one foot in the boiler and the other in the freezer.
So on average we have warmer summers. But not many bright hot days! You see when we have cloudier skies the clouds keep in heat at night. Thus with more cloud you get less cold nights, less cold dawns and warmer early mornings. On average the days are warmer but also cloudier and dimmer. Bright sunny summer days are rare now because of more water vapour there are more clouds. All fuel burnt anywhere releases huge amounts of water as well as carbon dioxide. And because of enormous quantities of dust when there is any sunlight getting past the clouds then it is dimmer than it should be. Some estimates reckon we receive a sixth less actual sunlight than before. I have found tomatoes and squashes harder to grow the last few years than when I first came here twenty five years ago and I am convinced it is the lower light levels, and secondly the lack of day night temperature differentials.
Many of our crop plants prefer cold nights and warm days -as long as it does not go too far either way, they do less well in more constant temperatures. And this all means that our simplest option for obviating coming weather changes, that of going under cover, may not work as easily as we may suppose. The light is already reduced and any glass or plastic, or netting or fleece, reduces the light still further, and by much more if it is dirty! Low light means weaker plant growth more prone to disease as we already know from winter croppping.
Growing under cover also alters the temperature differentials. By keeping off the wind and trapping warmer air the indoor temperature is kept above the outdoor. All well and good generally, except in scorching sunlight -which rare problem is easily prevented with shading. (How many of you remember how all greenhouses had to have white painted roofs only a decade or so ago!) More often though another problem comes with warmer nights especially under artificial cover abetted by cloud cover. Then the temperature may barely drop below that of the cool dim days. Night time cooling is as necessary as brighter days for many crops so we find they do not do so well under cover. Ventilation may help offset some of the heating but not all. (One way of achieving cooling on a small scale say in a cold frame or small border is with cold water bottles- plastic bottles of ice stood amongst the plants (NOT touching them), these will help keep the temperature cooler overnight.)
A similar problem affects many perennial fruits grown permanently under cover such as grapes and stone fruits which have a chilling requirement; they need a long cold period in winter to go fully dormant. Some are already harder to grow permanently under cover as they just do not get a cold period for long enough even if the ventilation is left fully open. Fortunately most can be grown in containers so they can be put outdoors in autumn and brought in after a sufficient cooling has occurred.
This same predicament will affect most other perennial fruit crops, starting with those such as pears and blackcurrants, which have large chilling requirements. As winters become milder, even with cold snaps, these fruits will not get sufficient chill days to go dormant. For this reason pears and similar are now not well grown in the western counties where winters are too mild for them already. We may change our varieties to cope by sourcing those adapted to milder winter areas; for example we may get better suited blackcurrants from New Zealand.
Likewise in the coming decades we may have to change varieties of many if not all of our soft and tree fruits, not to cope with hotter drier summers but with mediocre winters. So I’m sorry to dash hopes but it’s rather unlikely we will be able to grow regular crops of such as olives and citrus.
Now some unscrupulous purveyors have made much of the alleged hardiness of new sorts of olives. Olives have always been fairly hardy- I’ve had two outdoors for more than twenty years. The problem is with their cropping, which may well be improved. But olives, citrus, loquats and arbutus strawberry-fruits all carry their crops through the winter to ripen the year after flowering. Now, true, with milder winters these do have more of a chance. But climate warming is also giving us more unpredictable weather so the chances of completely frost free winters may in fact become much worse. And it only takes one freezing cold night to damage these crops irrevocably. So can you count on that not happening? Of course if you can help and keep the frost off with insulation or whatever and whenever it may be likely then you may get crops more often, but it is riskier than at first glance.
Generally then we will probably be growing much the same perennial fruit crops though eventually in different varieties, and hopefully more drought resistant. Of course a few already marginal crops, even olives, may sometimes do better. Apricots have benefited from the recent run of milder springs with fewer late frosts, peaches and Kiwis likewise. On the other hand dimmer damper summers have meant more mildew and rust problems on almost everything and these may be expected to get worse if the trend continues.
So despite the drawbacks including the need to water I guess we will end up growing more fruits in containers and moving them under cover for part of their annual cycle. As much to escape diseases as bad weather. Or for some in the ground we may place covers over them, sort of fruit cages come plastic tents, I already do to keep the blight off tomatoes.
Likewise I suspect we will prefer to grow more vegetables in pots and cells under cover and plant these out later. This will enable us to get round changeable weather and avoid sporadic late frosts and torrential rains and so on by reducing their time exposed outdoors. We will probably grow more crops on in containers. Certainly I get far better crops of sweet potatoes in containers under cover than from outdoor planted ones.
With milder winters and more cover we may grow some vegetables, mostly salad crops, almost year round. Although vegetables in dim light suffer the same drawbacks, and more so, as for the fruit we have had more practice growing them out of season and many more varieties are available. However many vegetables need large areas of ground and large crops cannot be grown in containers. Raised beds may well become more frequently employed to raise plants up out of waterlogged soil in winter or in summer. But the soil and crops may still suffer if the rain or hail are severe and frequent- cover is the answer again. So we will need more cloches and low tunnels if not walk in constructions. Though in the end we may find it simpler to cover our whole vegetable bed in one. Still after all what keeps the weather off will also keep out the wood pigeons and other such pests.