Beating the Heat: Watering.

We are quite lucky to have not been hammered by the temperatures in the mid-forties which have hit the east of the country, but a few days with highs of thirty-eight or nine has seen me getting through a lot of water. I have four large water butts to collect water from the roof, holding round 1500 litres, but a period of intense heat will see those emptied in just a couple of weeks.

Watering in the heat is often a matter of contention and not simply a question of 'just watering' but rather more complex - morning or night, on the leaves or down at the base, and critically how often? Well, the answer to all of that is if course a bit of everything, because it depends on the plants and also on how established they are. 


But one rule I do think is important is not to water little and often. In order to withstand the heat, plants need to keep themselves hydrated and for that they need a good root system. Keep the top centimetre of the soil moist and that is where the roots will stay; get the water down deep and that is where the roots will have to grow, seeking out the moisture. A deeper root system makes a plant more resistant to drought and also to rocking in the wind that can whip up when a summer thunderstorm blows through. Deeper roots also find more nutrients as the soil fauna like earthworms pull organic matter deep down.

Also, a soil which is only moist at the surface will dry out more quickly, while a soil which is damp deep down will be protected from evaporation by the dry layer above. This is also why I mulch; a layer of material above the damp soil protecting it from the drying effects of the sun and the breeze. And the presence of mulch means I favour watering at the base of the plant - there's no point pouring a can-full on top of the mulch, after all! 

There are exceptions, and that is brassicas all of which are attacked by the tiny flea beetle, a pest which thrives in the heat. Fortunately these beetles don't like high humidity so a a good watering of leaves, mulch and ground at the hottest point of the day helps reduce their impact. But this is definitely not the approach for most things - soft leafy plants like lettuces can be scorched if their wet leaves are hit by hot sun, as has happened to the lollo rosso in the photo above.

The final question is morning or night? Certainly more of your precious water will be lost if you water in the morning, especially if the water is going to sit on unmulched ground. When I see the iconic image of agricultural watering systems on sunflowers or maze spraying water into the sky in the middle of the day I do wonder how much reaches the roots and actually irrigates the plant. I have a lot of slugs, and although they are buried deep when the weather is hot, evening watering certainly makes life easier for them. I therefore water in the mornings. 

Even in the midst of a canicule, established heat loving plants like tomatoes or aubergines will only get a weekly water, along with a liquid feed. Newly established plants - lettuces, beetroots some herbs which are repeatedly sown and planted out throughout the summer - will get watered every morning.
Don't worry too much if leafy plants like courgettes or pumpkins appear to wilt in the sun: they withdraw moisture to avoid transpiration.

Only worry of the stems are breaking down, too. The leaves will come back but the stems may not. In this case give a really good drink to the base of the plant. It won't recover immediately, although chucking up some shade if you can will also help.

How we manage our water and our gardens is going to become more and more important as the climate warms. Whilst the prospect of growing mangoes or maybe even bananas is exciting, the implications are worrying - water well but water wisely!