Thursday, 25 July 2013

....now don't complain about the heat!

So, after a stunning couple of weeks of glorious sunshine we Brits are beginning to say those fate-tempting words.....'it's too hot!'. We are very hard to please, but I guess we are so unaccustomed to temperatures like this  - between 25 and 32 degrees centigrade, that when we finally get what we've been wishing for we are totally unequipped to deal with it. So if climate change is going to bring us more extremes like this, how can we be more resilient when it comes to growing food?

The most obvious place to start is water conservation. In the UK we have huge potential for collecting rainwater, usually from a roof area or pond, and in other less common ways such as creating swayles. So how much water do you need to collect? You need as much water as you would need to cover you through the longest potential dry spell....which in an increasingly unpredictable climate is very hard to estimate.....so I would say when it comes to rainwater harvesting - collect as much as you can!

Roof collection:

Two 200l water butts connected in series, intercepting a down pipe.
It is possible to calculate approximate water catchment from roof areas. Patrick Whitefield has the formula explained in The Earth Care Manual. It is essentially your roof area (measured as floor space to account for roofs which pitch in different directions and benefit more or less from prevailing wind) multiplied by the average annual rainfall where you live, plus some approximate estimations of run-off co-efficiency (leaks, evaporation, etc) and wastage from the filter. As Patrick explains there are many pitfalls to these calculations in the form of too many estimations, variables and unpredictability. Therefore I think it's safer to have more water butt volume than you think you need in order to benefit from extreme wet periods and therefore have more resilience in drought periods. If you are on a budget you could fit one water butt under each down pipe and if you find it fills very quickly, add another in time, and possibly another. There is no real limit to how many butts can be joined in series other than the space available.

Many water butts in series on an allotment site in Bristol.
Ponds:

A beautiful and useful pond in Paul & Hopi's polytunnel at Lammas is fed by a nearby spring.
Ponds are an asset to a food growing area for so many reasons - they bring diversity to the garden and therefore providing system resilience in the form of predatory insects and amphibians for example. But if your pond is big enough you can use it as a reservoir for watering as well. If you are able to site a pond high enough in the landscape, ie above the growing area, you can use gravity to transport the water to the growing area, and may be able to directly feed low pressure irrigation systems. Having said that, often the obvious place for a pond is a low, boggy area where water naturally collects. Siting a pond like this can reduce water logging problems and make use of an area which is difficult to grow in. These ponds may dry up in the high summer, so may not be very useful for watering from, but will still bring beneficial wildlife. If they are big enough and don't dry up you can use low power solar pumps (although these are sometimes not very efficient for moving large volumes) or if you have running water you can use a hydraulic ram which uses no power (other than that of the running water).
A water reservoir at Martin Crawford's forest garden nursery in Devon. Netting helps to keep out leaf litter and other detritus which will clog filters. It may also reduce evaporation.


Swayles:

Often confused with ditches, they are in fact the complete opposite! Ditches are used to direct unwanted water away, therefore they are dug on a Small gradient and flow. Swayles are dug on the contour in order to capture surface runoff and allow it to percolate into the soil. These are most commonly used in parts of the world where they have a wet season followed by a dry season, and increases the water levels in the ground to help get through the dry periods. They are not often used in the UK as we tend to have.....a wet season! But in drier places such as East Anglia they could be of benefit, especially if planting woodland or orchards. Of course, you would first need to find a slope, which in Norfolk or Cambridge may be a challenge!

Another way to conserve moisture in the soil is the use maintenance mulches to reduce evaporation and weed competition. We have been using old hay bales we have left over from our wedding - they made good seats and climbing towers for the kids! Now I know what you're thinking - grass seed!! Yes, generally it is risky using hay as a mulch because of all of the grass seed in it. However, these bale have been stored in our biggest glass house for 18 months and believe me, they have been well baked! We weren't planning to mulch this year because we sowed white clover in the vegetable beds (see prev. post) as a green manure/living ground cover around our crops. We had some success with this last year around our pumpkins and courgettes, so decided to use it in two more beds this year. Sadly the clover didn't germinate, despite repeated sowings, so come the heat wave we did some last minute mulching to save our soil. This is especially important for us as we're still trying to build up the humus in the very poor soil in the raised beds, so it needs all the help it can get. Having high humus content in your soil is probably the best way to retain moisture and can be achieved by simply adding lots of good organic matter each year in the form of compost, animal manure and green manure.

One of our wwoofers mulching with hay in a raised bed here at Tawny Oaks. The odd small patch of clover is visible amongst the hay.

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