The current and historical practice of controlling our irrigation is reliant on timers.

Yes, after years of technological advancement, it seems the most favoured method of controlling an irrigation system is still estimating - or guessing - how much water is needed. It may be easier and less complicated, but is it best for our plants and for our unsustainable and ever depleting water supplies?

Landscape professionals have different levels of knowledge and expertise, but ultimately a professional, homeowner or otherwise, will be assuming how much water is required to sustain the life of a landscape. They may discuss things like adding a rain sensor and what type of sprinklers are being used. Some water retailers recommend applying a standard drink of 10 millimetres. But what does a standard drink actually mean? We are not down the pub have a few cold ones; these are plants that need specific amounts of water.

Let’s look closer at the nominal application rate of 10 millimetres. Is this 10 millimetres during peak season (summer) when the temperature is 30 degrees Celcius full sun, or is it 10 millimetres for a peak season (summer) when on that day, it was overcast and temperature only had a high of 23 degrees? Is this 10 millimetres for a warm season turf such as couch or kikuyu, or is this for a lush landscape using exotic plants or even a native planting?

The point is, there are many more factors to good efficient watering that vary widely from geographic locations all over Australia, to micro climates within that one state, to differences between suburbs and what type of landscape the homeowner has preferred, even how the irrigation contractor has designed and installed the irrigation system.

So how do you program a timer for irrigation?

The first setting is what days you think you want to water during a week. This decision may be forced on you through water retailer restrictions or a lifestyle choice of no watering on the weekends or just making sure the kids can play outside. You can’t mow the grass on the weekend if it is getting it too wet. Setting the frequency of these days or how often you want the watering such as every day, every second day only on Sunday, Tuesday, Thursday and Friday. There is some guesswork in this.

Next, we have a number of automatic solenoid valves in an irrigation system that are unable to water everything at once. This is usually due to the limiting factor of not enough water and pressure, but you should also consider the different plant areas or hydro-zones of the garden and therefore the different method of how you apply this water to each section by using either dripline, sprinkler with sprayers, sprinklers with rotary nozzles or larger gear driven sprinklers.

The quantity of these valves could be anywhere from one or two or all the way up to over 80 or a 100, depending on the size of the area requiring to be irrigated. If there are too many valves, you may need to operate multiple valves simultaneously to ensure there is enough water sprinkled over the property when the plants really need it. Like marathon runners who need to replenish themselves and hydrate, plants need that water now, not later. Each valve must have a certain amount of run time allocated to them so the solenoid valve or zone will remain open and allow the water to feed through the sprinklers. Again, there is some guesswork in setting these durations.

Our last step is programming the controller when to start. Ideally, this will take place in the early morning as the sun is dawning and the plants are waking up. This can reduce any stagnation of water or plant disease (mildew). Unfortunately, when you have a larger number of valves or shifts of irrigation, it is often necessary to start late at night to allow all areas to receive water and to hopefully ensure off-peak power cost. If at all possible, irrigation should never occur during the day when there is higher evaporation, effectively wasting the effectiveness of the watering and losing money in water costs.

The million dollar question is, how often is a program changed during the course of 365 days, through different seasons, in different within those seasons? Does a user check the previous day’s weather, check the upcoming forecast, physically go to the controller, and adjust the run times? All too often, the answer is no; they may not even do this monthly. They may just do this once a year when they turn the system off and then back on again.

Weather based controllers have more options to micro-manage each zone, allowing for detail to be entered about each area of the landscape daily. They will, however, never irrigate other than when you want and won’t start the irrigation other than when you want. What they can do is build up a water requirement and decide the amount of run time required to replenish the lost water caused by evaporation and plant water use for each individual zone based on years or research. You are still the decision maker regarding what type of landscape you want: just alive, active and healthy, or lush strong growth.

Here are a few things to monitor to ensure your irrigation system is working effectively:

  1. Weather stations for receiving daily high and low temperatures plus rainfall data. Additional inputs such as solar radiation, wind, humidity, and dew point can assist in improving accuracy. These units have come down in cost and can be installed on the actual site for accuracy or using online connected smart technology to a number weather, web related sites. Whilst these may have a higher accuracy in terms of the data, they can lose their accuracy if the actual weather station is simply too far away for the actual irrigation site.
  2. Input for the type of sprinkler or emitter that is used on that irrigated site. The controller must be able to incorporate this data for the individual solenoid valves or hydro-zones that are required when irrigating. This determines when the irrigation is operating how much water is being applied and what rate. This is typically in millimetres per hour.
  3. Input for the type of plant on that irrigated site. Once again by solenoid valve or zone, allowing the system to determine whether that plant type requires little to no water in order to actively grow or higher amounts of water. Such examples may be native type trees and shrubs for little water or annuals, cool season turf requiring a higher water use.
  4. Input for determining the soil type and the slope of that particular area of irrigation. Soil types have different infiltration rates and when used in conjunction with the above sprinkler rate of application ensures the water is applied in a manner that will allow the water to absorb into the soil profile as opposed to ponding or puddling on the surface or running off down the slope.

Shown below is a basic example of this concept. A quick look shows one reason why it doesn’t always get a high priority on all sites: it can get quite complicated. However, when we look at some of the opportunities of potential cost savings from sports fields, commercial property, fast food chains, and residential it suddenly becomes attractive for a second look to satisfy the perception and aesthetics of the community.

As you can see, not everywhere is the same and the figures in these tables are based on long-term averages for a full 12 months which is not typical irrigation. Without the above inputs and a set-and-forget approach from a simplistic on/off timer, it's clear this can waste a tremendous amount of water as opposed to the ever growing weather-based controllers on the market.

NB: Weather Based Calculations are based on Crop Factor 0.80 for Strong Growth, Average Epan (mm), Average Rainfall (mm), Irrigation Efficiency (.75) as sourced from Bureau of Meterology

  • I really appreciate this article. There is a lot of good food for thought.