21-day lockdown – Day 19 – Irrigation by the numbers


21-day lockdown – Day 19 – Irrigation by the numbers

In our water-wise gardening article on Sunday, we discussed some of the ways you can reduce your water requirements for your garden. Some of these included reducing the size of your lawn, making use of indigenous plants, keeping already existing ‘exclusion zones’, and using mulch extensively in your garden. But today we thought we’d walk you through a real-life example, and give you some basic figures of how much water you can actually save by reducing the size of your lawn and switching to a water-wise garden.

In some ways this article was prompted by requests we sometimes receive from home owners for more lawn in their gardens, without them realising how much that lawn is going to cost them in terms of watering.

Perhaps the biggest example of this was when a home owner requested that we remove his entire 7000 square meters of indigenous grassland, and replace it with kikuyu lawn and an irrigation system. His reason for wanting to do this was because the family was scared of snakes – something we could sympathise with – and he didn’t want to encourage them to be on his property. But instead of removing all of the grassland, we tried to persuade him to keep some of it, and plant up only some areas as lawn, specifically those closest to the house. We pointed out that he essentially had his own private ‘nature reserve’ on his property, and that it wouldn’t need any irrigation (it had survived for years without it). All we would be doing as landscapers would be to create pathways and seating areas, and make it accessible and functional. We would also add in some new indigenous species that would enhance the area, and were suited to an indigenous highveld grassland. We then showed him the figures of how much water he might need if he replaced his grassland with kikuyu lawn, which, based on past research on healthy green lawns, would have been around 25mm of water per week. The calculation therefore was: 25mm x 7000 square meters = 175000 litres per week. In other words, in order to adequately water his new lawn, he would have to use the equivalent of 17.5 ten-thousand litre water tanks every week.

Unfortunately he did not have access to borehole water, which would’ve mitigated some of the costs, and due to regulations within his estate he wasn’t allowed to install one. All of his water would therefore have to come from either his municipal supply, or be supplemented by a rain water harvesting system. In the end, as much as we tried to persuade him otherwise, we eventually turned the project down. We simply couldn’t fathom taking out 7000 square metres of indigenous grassland in favour of kikuyu. As landscapers, I think we have a duty to try and enhance the biodiversity of our country, and to help save water. If we can do this by swaying our clients to this way of thinking then that is the ideal, but it also means that sometimes, no matter how lucrative a project may be, we have to be willing to turn it down.

So today we thought we’d give you some of the figures – on a smaller scale – of an irrigation system, so you can see how much water is actually being used. As one of our irrigation mentors once said to us: “if you showed these figures to a client they would never install an irrigation system!” We still believe an irrigation system is a worthwhile investment in certain situations, specifically for areas of lawn, or for vegetable gardens, or for newly established gardens. But it is also worth knowing exactly how much water you need for your garden, so that you can make informed decisions about your new garden layout, and how much it’s going to cost you.

To illustrate the point, we’ve taken the design of a small garden we completed recently, for one of our clients in Bryanston. They were struggling with their lawn, which was lumpy and not doing very well.

After a few discussions with them, and going through some ideas, they were brave enough to decide to completely remove their lawn and replace it with an indigenous garden. We used Silver Carpet (Dymondia margaretae) and stepping stones as the pathway to meander through the garden, and then added interest by creating contours as well as three main focal points: a Lavender Tree (Heteropyxis natalensis), a Crane Flower (Strelitzia reginae), and a bird bath. They also decided to forgo installing an irrigation system – it was after all a water-wise garden – and instead they would water it manually.

Below is the design, photos from the installation, as well as the estimated watering figures between the original lawn and the new indigenous garden. We’ve included two sets of figures for the new garden, one that is relevant now, and one we believe will be relevant in two years once the groundcovers have become established.

The garden design

Removing the lawn and preparing the ground

Creating contours and leveling for the pavers

Checking measurements for the position of the Strelitzia. This type of detail is not necessary in a large garden, where using your eye is usually more appropriate. But a few centimeters left or right in a small garden can make a big difference, so here we used a combination of measurements from the design and our eyes to choose the position for both the Strelitzia and the Lavender Tree.

The measurements for the builders

The pavers in place, and the main groundcovers and shrubs planted.

The completed garden. Now we just need it to grow – watch this space!

And here are the designs again, with the associated watering figures for comparison. Note the last column in the tables, which represents the estimated monthly water usage:

Recommended schedule for 1-2 years

Recommended schedule from year 2 onwards

In summary, the old lawn would have required up to 2800 liters of water every month in summer, indefinitely, to keep it looking green and healthy. By contrast, the new indigenous garden is estimated to require only half that amount (1400 litres) for the first two years, and thereafter less than a quarter (500).