Helen McKerralIrrigation

Water restrictions… grrr! Don’t get me wrong – I’m not into wasting water, and sensible Adelaide gardeners familiar with our notorious mains supply have been watering early morning/ late evening decades before ‘permanent water saving measures’ imposed it. Who wants garden plants resembling steamed spinach? It’s commonsense, which is probably why on an interstate trip a few years ago I drove through several Victorian council districts where watering lawn median strips – and bitumen! – on a windy forty degree day at noon apparently made sense to someone without the common variety. Town after town… even as SA irrigators were bulldozing orchards! Arrrggh!

Drippers are popular but, in my opinion, not all they’re cracked up to be, especially in clay soils like mine, and even after decades of improvement. Slower infiltration rates create a shallower wetting profile compared to sands as you can see in Soil Type Influences Irrigation Strategy publication from Michigan State University.

Two or three hours weekly concentrates plants roots in a small area near the surface, so the first missed watering has catastrophic results. Fine misting microsprays are even worse. In heavy soils, you apply water more slowly and for much longer: I water less frequently, but for longer.

I’m convinced that my original watering regime worked in my garden. I left sprinklers on for at least five hours at night… but only once every four to six weeks, even in summer. Frequency varied – I piggy-back rainfall whenever possible – but I’m sure this regime created plants with deep, wide-ranging roots resistant to extended dry conditions. Of course, my microclimate is protected from wind and late afternoon sun, and without subsurface sheet rock, so I’m lucky. Even my camellias all survived. The only one I had to rescue with a hose was on day six of a heatwave. It managed almost a decade of drought so it deserved to live!

Yes, rain gardens are sustainable but, for many gardeners, a limited palette. Far fewer vegies or fruit trees for me, at least not without huge storage capacity. This is why Adelaide’s status as the ‘longest time between rainfall of all Oz capital cities’ is critical, because tanks aren’t replenished.

Water restrictions that, in practice, promote garden beds over lawns, are ridiculous. A lawn is more valuable to families with young children, but thousands around Australia were never given that choice (new subsurface irrigation systems are expensive and require root-inhibiting chemicals). Why not allocate an amount of water, based on the number of residents, and let homeowners choose how they use – and apply – the water? Exceed the amount, get slugged more. Extend the current system, with a base allocation (currently 30KL per quarter at $1.93/KL, jumping to $2.89/KL after that) but incorporating number of residents to make it fair for large households, and increasing prices of higher tiers to discourage waste.

SA Water has come a long way with a range of useful fact sheetsHowever, their watering plan is, in my opinion, problematic – any experienced gardener will see why when you play with it.

Since installing tanks, I stopped obeying water restrictions to the letter. In recent years, not watering how I was told to, my mains water use has been zero April/May – September, when we use rain water. Even in January-March, with two residents and on 100% mains, our daily usage has been:

2008 187L (approx)

2009 187L (approx)

2010 289L

2011 130L

2012 376L (but with 3-5 residents this year)

The table in the slideshow is from my Jan-Mar 2012 bill and it puts our consumption into context. At 700sqm, our garden was ‘medium’, and figures are for ‘water-wise to average’ households. Normally, we’re ‘one person with no garden’. Even this year’s 376L, with three to five residents, is equivalent to two people with no garden, or one person with a small garden. Of course, next year our garden will be fifty per cent bigger than the large category.

So how do I water in the driest months? Every ten – twenty one days (more for vegies/fruit trees, less for ornamentals, with many areas receiving none; an extra sprinkle in heatwaves) with adjustable 360 degree offline drippers (on Page 4 of the catalogue) from 19mm pipe, NOT set to one universal ‘recommended’ rate. I instead use different numbers and rates for different slopes and plants, and adjust for different water pressures at upper and lower ends of slopes. Application rates need tweaking for the new area – slope and friability vary – but, as long as I keep tracking below ‘water-wise’ households in the seven months of the year when I use mains, I won’t be worrying about future water restrictions/rules. For example, I’ll piggy-back on natural rainfall even if it’s an ‘off’ day, rather than follow the rules and use double the water three days later. It’s commonsense.

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Helen McKerral

About Helen McKerral

Horticultural journalist, photographer, contributor to many garden magazines, and author of 'Gardening on a Shoestring'. Adelaide Hills, South Australia

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