Rainwater harvesting tanks

Following on from my last blog garden writer John Walker has emailed me an alternative suggestion for sources of tanks for rain water harvesting:

“I bought my tank from www.smithsofthedean.co.uk, who sell recycled 1500
litre tanks and a good range of smaller ones, too – click on ‘recycled
containers’. These were lovely people to deal with – they even rang me
up when the large tanks came back into stock. Dealing with them and
delivery of the tank was a real pleasure.”

Garden News Article Twenty: Water harvesting, green manures and intercropping

I’ve only got six more articles to go for Garden News now until the end of the year. Here’s Number Twenty:

Following two summers of almost continuous rainfall it seems hard to believe that this time three years ago we were coming to the end of one of the driest summers on record. The need to engineer our garden water supply to balance out the peaks and troughs is obvious. We can’t determine the amount of water that falls on our gardens but we can control how much we collect, store and use.

A friend of mine reckons he can survive anything but a cataclysmic drought with a drip feed irrigation system that combines a large rainwater harvesting tank (available cheaply from The Tank Exchange – see below for contact details), a grey water recycling system that runs straight from the pipes underneath ever plug hole in the house (grey water being water that has already been used but can be used again for some lower order process that does not require clean drinking water) and a series of irrigation pipes running along the surface of the soil. The plants receive a regular supply of water automatically every time he pulls a plug – though this doesn’t stretch to toilet water (known as black water), which quite rightly goes straight into the mains sewage treatment system.

If you can’t do any of this for logistical reasons (I can’t) or even if you can, the simplest way to guard against weather extremes is to make sure your soil contains loads of organic matter. This is engineering of a different kind. Organic matter regulates the amount of water that remains in the soil around the roots of your plants. In very wet years a soil rich in organic matter will be less waterlogged because it will have a greater number of worms and other soil organisms; all of which help to create drainage channels that improve the flow of water from the top soil to the sub soil. In very dry years organic matter helps to keep water near the roots of plants. It does this by turning particles of soil that are too small to hold water into large crumbs that can. Each crumb is wrapped in a thin film of liquid that roots penetrate to draw off water.

Adding compost to the soil is one way of building up organic matter but you could also use intercrops (extra crops grown between rows of regular crops just to add organic matter to the soil) and green manures, both of which do the same job. An intercrop could be something as simple as grass grown between rows of trees in an orchard. The grass keeps soil in place and stops erosion. Every time the grass is cut and left to rot extra organic matter is added to the soil.

Mostly though intercrops are red clover, beans and other legumes sown in between rows of vegetables, cut before they seed and left to rot. The cut crop acts as a mulch – stopping water evaporating from soil on hot days – and provides food for soil organisms (in the same way that compost does).

Green manures (crops grown specifically to add fertility to the soil) are more commonly grown in crop rotations (in gaps between sowing) but can be planted on any patch of bare soil waiting to be planted up. They include: alfalfa, buckwheat, fenugreek, field beans, lupins bitter blue, mustard, phacelia, red clover, ryegrass, sunflowers and tares. Each one has a different function, growing pattern and harvesting time so you’ll need a guide (see below) but the general effect of all is to increase the volume of organic matter in the soil.

Resources
Garden Organic publish Green Manures:a step by step guide (priced £1.35 from www.organiccatalog.com 0845 1301304)
The Centre for Alternative Technology publish the tipsheet Making Use of Greywater in the Garden (priced 50p from www.cat.org.uk/catpubs 01654 705959)
The Tank Exchange sell large recycled water containers for garden use (www.thetankexchange.com 08704 670706)