Welcome to our seasonal newsletter, aimed at helping garden enthusiasts discover better ways to use our most precious resource, water. While we are all aware of the potential problems South Africa and other countries in the world are facing in securing and delivering sufficient water to their populations, most of us are unsure as to what we can do to help avert this crisis. This newsletter aims to show you various ways to save water each season, helping you to maintain a lush and beautiful garden, while still making a significant contribution towards saving water. For more watering tips and articles on water conservation please visit our website.

Autumn officially started on 1 March, and even though high temperatures make it feel like it is still summer, leaves have already begun to fall. Some plants will still be actively growing, but many will be moving into their seeding and fruiting phases, and as the temperature starts to drop they will begin preparing for their dormant winter period. It is critical during this time of year to make sure you don't overwater. As the temperature drops and plants stop growing, the amount of water you give your garden must reduce too.

Watch out for hot snaps as summer leaves us, and be sure to increase your watering frequency during these periods. High temperatures increase evaporation and dry your soil out rapidly. Plants cannot tolerate dry soil for very long and will begin showing their objections by wilting. Water also provides an important cooling effect, which is essential to the wellbeing of your plants.

How much water does your garden need?

A simple way to see whether you are giving your garden sufficient water is to dig a hole (about 15 cm deep) and inspect the soil at this level. If it is soggy and pooling, you are over watering. If it is dry you are not watering enough. What you want is a happy medium between the two; a nice moist soil.

The trick is to not let it dry out for too long. Soil loses water due to two primary processes: evaporation and transpiration. We are all familiar with evaporation which increases as temperature increases. Evaporation is highest in summer and lowest in winter. You may not have heard of transpiration, but it is just a fancy word for the water lost due to plant usage. Once the water has carried nutrients through the plant, it returns to the atmosphere in the form of water vapour.

The combination of water lost through evaporation and transpiration is called evapotranspiration, ET for short. The correct amount of water to give your garden is equal to the ET since you last watered. This will replace exactly the right amount of water and keep your soil nice and moist.

Picture courtesy of Wikipedia. 

So to provide your garden with the right amount of water you have to replace the water lost due to ET. But what does this mean practically? How often should you water and for how long? To answer this question we will use as an example a typical garden which is as close to the average as possible. We will assume our garden has kikuyu lawn, well established shrubs and a loamy soil. The average ET in a typical summer in South Africa is approximately 25mm per week, and this reduces to about 15mm in autumn. This means we need to replace 15mm of water each week to keep the soil moist enough for our plants to thrive. During hot spells you need to increase this to 25mm to ensure the soil doesn't dry out.

You need to water fairly frequently during autumn to ensure your soil doesn't become dried out, but not too frequently otherwise you will discourage deep root establishment, and compromise the hardiness of your plants. A good practice is to water your garden twice a week in autumn, unless it is extremely hot in which case you can increase this to three times a week, or every second day. 

So if you are watering twice a week, this works out to about 7.5mm per watering day. Each time you take out that hosepipe or switch on the irrigation system you will need to ensure that you distribute 7.5mm of water evenly across your entire garden. Sounds simple, but how do you do that?

If you are watering by hand or using a sprinkler on the end of a hosepipe then you will need to know how much water is flowing out of the tap. We call this the flow rate. A flow rate has a unit of volume, such as a liter, and a unit of time, such as a minute. A typical flow rate may be 30 liters per minute. Your flow rate will be unique based on the area you live in, the size of your water meter, the size and length of pipe leading to your tap, and the size and type of tap you have. The best thing to do is to measure it yourself so that you have an accurate reading. Here’s how to do it.

You will need a bucket and a watch. Place the bucket under a tap and open it fully. Time how long it takes to fill the bucket. For example, it may take 20 seconds to fill a 10 litre bucket. Your flow rate is 10 litres every 20 seconds, or ½ litre every second. This is equivalent to 30 litres per minute.

Once you know the flow rate you can work out how long to water for. Every litre of water on one square metre (1m²) of garden is equivalent to 1mm of precipitation. So to apply 7.5mm of water to the garden in our example we will need to put down 7.5 litres on every square metre. We know that the flow rate is 30 litres per minute so 7.5 litres will take just 15 seconds to apply. For a 100m² garden (about the size of a townhouse or small cluster) this means about 25 minutes of watering every second day.  It's as simple as that!   
 

If you are using an irrigation system you will need to know the application rate of your irrigation system. A typical irrigation system has an application rate of 40mm per hour for cone sprinklers (these are pop-up or standpipe nozzles that don't rotate) and 10mm per hour for rotary sprinklers. If you need the exact application rates for your system consult your sprinkler manufacturer’s specifications. For more information on how to calculate precipitation rates see here.

That means you should run your cone sprinklers for about 11 minutes, twice a week.
For rotary sprinklers you would run your system for about 45 minutes, twice a week.

There is of course a much simpler way to achieve these results! If you install a smart controller, the system will calculate exactly how long to run for based on the prevailing weather conditions in your garden. This clever product calculates your garden’s specific ET and adjusts run times to apply just the run amount of water. With a built in rain sensor, the system will also adjust to ensure you don’t overwater when it is raining. For more information about product which will save you time and money click here.

Watch out for more smart watering tips in our winter edition of this newsletter.

Happy gardening!

The following subscribers entered our Smartline competition and were selected to receive their very own Smartline water management system. Well done to Erwin Dorfling, Theo Coetzee, Frik van der Linden, Eve Shead, Glenn Hurlow, Flip Joubert, Eric Gunning, Johann van der Westhuizen, Peter Pretorius and Marie du Plooy. The winners have been notified and must contact the Wetec team to receive their prize.