In the early history of gardens, irrigation and gardens have always gone hand in hand. Let us set aside the treasure-trove that is Chinese Gardens, at least for the moment. With much of the civilisation that shaped western thinking developing in the middle eastern belt from Egypt, through Mesopotamia to Persia (Iran), dry summers were the norm. However, rivers fed by mountainous regions were also part of the development of these communities – none is perhaps better known than the Nile. Certainly gardens were well documented from at least four thousand years ago in Egypt. Irrigation was a way of life in Ancient Egypt (as it was for all these cultures). Great growing seasons in the warmer months were only possible through the channelling and storage of river water. Ponds and rills became a permanent fixture in the earliest decorative gardens. In the last in this series – ‘H is for Hanging Gardens’, I mentioned Sennacherib’s Garden of his ‘Palace without Rival’, in Nineveh. Stephanie Dalley (to whom I alluded in the last blog) posits that the gardens were watered by an 80-kilometre (50 mi) series of canals, dams, and aqueducts used to carry water to Nineveh with water-raising screws used to raise it to the upper levels of the gardens. from there the water descended by gravity through the gardens.
Gardens in ancient Persia may well have pre-dated those in Egypt – they certainly devleoped around the same time. However, whereas in Egypt there were rills and ponds, used for bioth pleasure and irrigation, in Persia these took on a mystical signicance. By around 700BC, gardens were divided into four quarters by four rills or channels. these channels represented the four great rivers of Paradise – Euphrates, Tigris, Gihon and the Pishon. Incidentally, Hindu belief also has four great rivers, as does Buddhism. This Persian tradition is particularly relevant to western garden design as it is through this route (see A is for Alhambra) that symmetry and formality entered the canon of the great Renaissance Gardens. Of course by the time they had filtered their way through to northern Europe, these rills, channels and ponds were much more for decorative effect than for irrigation.
Which sort of brings us to the present day. Irrigation plays a key role in gardens today. It starts with the irrigation of the plants and trees in the nurseries that supply them, but it is really the end user that interests me here – should we irrigate our gardens? And if so, how, and when? It is easy to take a black and white view on this, but as always, that masks the reality. I recently asked an irrigation consultant what the purpose of irrigation was, and he gave me an interesting answer: “To establish a plant and allow it to develop a healthy root system, so it can survive on its own without irrigation.” To my mind, he talked far too much about lawn irrigation, but the principal of establishment supports my own view. Of course, it goes without saying that we should adopt other measures first – selection of suitable plants, addition of organic matter to aid water retention in the soil, mulching to reduce water loss, etc.
In the matter of establishment, he was interesting. “Far too many people irrigate every day. Better to irrigate once every three or four days, but during the night – perhaps in several bursts. This mimics natural rainfall and allows the water to drain to the lower profiles of the soil. It also reduces loss through evaporation, and forces plants to root more deeply to reach the water.” This is the practice that I have mostly followed in my own garden during hot weather – I only water every few days (often late in the evening), and other than the kitchen garden, only newly planted specimens. Wherever possible, I used retained rainwater instead of mains water – I have four metre-cube storage containers for the purpose.
I mentioned lawn irrigation – for me this is madness. We still have arguments with clients over this and probably give in at least once a year. There are several reasons why lawn irrigation is not a good idea. Firstly, it encourages shallow rooting – modern lawn grasses will not root deeply if adequate water is available. This in turn compromises their take up of nutrients making the need for fertilisers more likely. Secondly, it is wasteful of water – irrigation of lawns is delivered through sprinklers, whereas most planted areas are watered through drip irrigation. The latter is much more targeted – it delivers exactly the right amount of water to the plants roots without loss, instead of spraying through the air where up to 25% can be lost to evaporation, especially in hot weather. Finally, new planted shrubs will generally die in hot weather if not watered. Lawns do of course need watering to establish, but this happens relatively quickly. After that – let them go brown. The ‘leaves’ of the grass die, but the plant goes into dormancy and the lawn will green up again in no time once it rains.
Of course, this whole discussion about irrigation begs the question of plant selection. If we selected the right plants in the first place, would we need irrigation in gardens? The answer to this is probably that we inevitably need some watering for establishment, but after the first year or two it should be fine – if we have the right plants. During hot weather, most things in our garden do fine. Those that don’t are the ‘wrong plant, wrong place’ to misquote Beth Chatto. When we first moved to our house, we planted some Hydrangea villosa, which I love, but on our thin sandy soils they struggle in summer. Likewise the large Hydrangeas that we planted next to the swimming pond. They always struggled during dry weather. “Let them die” said Vicky, somewhat brutally. “I never liked them anyway. Wrong colour.” Last summer, I did finally ‘let them die’ and we are planting something more suited to our dry soils. The truth is that once established, most gardens do not need irrigation at all, or even hand watering. So, as we approach another hot summer, ponder on your plant choices.