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Landscape

Water-wise Gardening – Where are we?

A great post by

Marijke Honig. Published in The Indigenous Gardener, February 2017

 

 

As a landscaper, I feel we pay lip-service to water conservation in the landscape industry. Despite the liberal use of the word ‘water-wise’ on plant labels at nurseries, and during design presentations, the fact is that many gardens and landscapes are watered at least twice a week, and often three times.

While some indigenous and water-wise species are indeed adapted to drought, the way that we water (too frequently, not deeply) prevents them from developing strong, deep root systems. Instead of ‘making rain’ with our irrigation systems – giving a long deep watering – we wet the leaves, mist the atmosphere and moisten the top few centimeters of soil – only to have most of it evaporate soon after. Crazy, isn’t it? When one considers that most gardeners are using treated potable water on their gardens, it becomes even more incomprehensible. Imagine emptying 500 bottles of mineral water in one area of your garden – this is the typical water-use of ONE station of shrub sprayers.

Clearly, it is time for a major rethink.

What is a water-wise garden?

Is a water-wise garden one that is watered once a week, or once a month during the dry season? Or not at all? Or since rainfall varies widely across the country, should it be a relative measure?

There is currently no benchmark in the industry for a ‘water-wise garden.’ It is a vague relative term that implies ‘less than usual.’ Personally, I think this is not good enough! Fourie Petersen suggests water-wise landscaping should be based on a philosophy of sound ‘water management practices’. And ‘management’ requires measurement. Imagine if all landscapers always installed a water meter and rain gauge at each site, and organized weekly data to be collected and submitted to a regional/ national database? If we measure the amount of rain and water applied to landscape, we will have an accurate record and understanding of water-use, and be able to develop a benchmark over time.

Our relationship with water

Is it fair to say that water restrictions help to increase general awareness and appreciation for water? I think so. Switching off automated watering systems has brought us closer to our gardens: we are now tuning into plants and their needs and having to make tough decisions which ones are going to receive the grey water. My pots have never looked better since I’ve put a plastic basin in the kitchen sink for rinse water – it provides a few liters several times a day. In the days when I still had a bath with my young son, and it took me ten full buckets to empty it, I realized that even a shallow bath used a hundred liters. Needless to say, we have been showering since!

Saving and storing water

As landscapers in the Cape, we are often faced with the question of whether to install water storage tanks. This has led to healthy debate when one considers the following:

  • The Western Cape experiences a long dry season – often 4-5 months with no rainfall

  • One irrigation cycle can require 5000 -10 000 liters for a medium to large garden, so one can empty a full tank in one watering cycle

  • Tanks require space and have a visual impact

  • Water is pressurized with a booster pump, so electricity is used

  • Tanks are made of plastic, which has a significant environmental footprint

Looking at the above, it would suggest the value of storage tanks is questionable in the Cape. However, it is predicted that as a consequence of climate change, rainfall will be more erratic and less sharply seasonal. This summer in Cape Town seems to be a case in point: we received a big rainfall event in December and another downpour a month later – very unusual for January.  If gardens were properly zoned into water-use zones, a full tank could last much longer, when used judiciously for selected high and medium water-use areas. Watering will make the difference between Scadoxusflowering, for example, or barely surviving during a long dry summer.

 

Storing rain water has another less tangible benefit: it brings us closer to the weather and rainfall and increases our appreciation of water. Recently I visited my friends who had put a 200-liter plastic drum under a gutter in their courtyard. It seemed so insignificant compared to the 2 x 5000-liter storage tanks they already had, but Pat pointed out it was enough to make 200 liters of foliar feed for his veggies. He requires unchlorinated water to make activated worm compost tea, so the rainwater is valuable. This experience has shifted the way I think: even small water storage tanks are worthwhile.

Understanding water in the soil

In his excellent book The Water-wise garden’ (Penguin Australia, 2008) Jeffrey Hodges explains how plants use water and the way water is stored in the soil. I found his book fascinating, and the chapter on ‘How water works in your garden’ has transformed my watering practices. Understanding the physical aspects of water and soil has changed the way I look at water. He describes that ‘when water falls onto the ground, either by irrigation or natural rainfall, soil scientists divide it into 3 categories’ (notice only a small portion of it is actually available to plants):

  • ‘Run-off water is water that washes off the surface without soaking into the ground. It may cause erosion and is unavailable to plants.

  • Gravitational water is the water that soaks in and drains away into the subsoil – not available to plants.

  • Capillary water is the water that remains ‘stuck’ in the smaller pore spaces of the soil – this is the water which is available to plants.’ This water which surrounds the soil particles is what root hairs and mycorrhizal threads (mycelia) can absorb.

It is worth noting that the free capillary water keeps moving up, towards the surface, as water evaporates into the atmosphere. It is as if water is constantly sucked up through the soil. This is why a thick layer of mulch really helps because it cools the soil and slows down the upward movement of soil water and loss to the atmosphere. Hodges explains that ‘as soil dries out, the moisture films around soil particles become thinner and at a certain point the root hairs cannot ‘extract’ the water, because of strong attractive forces holding the water to the soil particle.’ At this point – called permanent wilting point – the plant goes into water deficit.

Above: Sketch from ‘The Water-wise Garden’ by Jeffrey Hodges Raindrops that fall on bare soil damages its structure. Covered soil remains undisturbed and the water soaks in where it falls.

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