In the July/August issue of Landscape Trades, I introduced the sustainable irrigation systems installed in the Landscape Ontario/University of Guelph trial gardens in Milton, Ont. The old irrigation systems were removed and replaced with state-of-the-art design, products and installations. This article will describe subsurface irrigation in the raised annual beds around the building in detail.

Gillian Glazer of John Deere and Dean Armstrong, eastern Canada sales manager of Hunter Industries, provided the product for the front entrance island planter. The system utilized Hunter’s Professional Landscape Drip Line PLD-1.0-12 to create the subsurface annual plant bed irrigation system. The drip line is buried 100 mm deep, with row spacing of 30 cm in a triangular grid pattern. The triangular pattern is the key to success, as it spaces the emitters 15 cm apart from one row to the next. This provides even distribution of the water to the plants’ roots through capillary action and is virtually an unseen system.

A newly released Hunter DC (battery) multi-station controller was combined with a rain sensor to prevent watering in the rain, saving 12 per cent or more of the water with the added bonus of not drowning the plants by overwatering. As there is no power available at this location, the battery-operated controller is excellent for this application. It is mounted on a 4x4 post at eye level for ease of scheduling. The controller is directly across from the valve that operates this system, so the wire runs are very short and would be very easy to troubleshoot in the future if any wire-related problems were to occur. Spare — homerun — wires have been run from the valve box to the controller for future use, as is always my practice. We used a Hunter Drip Zone Control Kit model ICZ-101, a low volume (drip) station control. The valve is housed inside a 1419 rectangular valve box, with a 15 cm gravel sump placed below the valve to facilitate drainage (from rain, not irrigation) and for ease of access for periodic maintenance of the inline filter, or to manually operate the valve.

Drip line tubing was installed in the excavated planter area. It was important to very accurately install the lines 15 cm from the planter curb, with adjacent row spacing of 30 cm being maintained throughout the rest of the grid lines. It is critical that the spacing is not disturbed while soil is being moved over the tubing, so the lines were held in place with over 100 inverted tubing hold-down stakes. The annuals and perennials that Rodger Tschanz, trial garden manager from the University of Guelph, and his crew were to plant, once our work was completed, were to go no further than the grid could supply subsurface water. This meant that the grid extended 1.21 m towards the middle of the planter.

Air/vacuum relief valves were added to the end of the drip line tubing to expel air from the lines as the water filled the tubing, and to open to allow air into the tubing once the water shut off, to prevent the tubing inline emitters from becoming suction devices, drawing dirt into the tubing. The device was mounted on a compression fitting T, so that one end of the T was fitted with a plug that was easily removed, turning the T into a flush valve as well. This allowed any debris to be flushed as the lines were filled with water for the first time, for winterizing and for routine maintenance.

The system in operation
So, what was the end result? Let’s look at the same location as if we had installed a conventional spray irrigation system. What is the water use for a spray system, compared to the subsurface drip line emitter system?

• 200 x 20 ft. with sprinklers spaced approximately 12 ft. apart = 49 sprinklers spaced approximately 80 per cent of radius for closer coverage and higher uniformity
• 49 sprinklers x 15 ft. half pattern @ 1.85 gpm @ 30 psi = 90.65 gpm
• 90.65 gpm x 10 minutes = 906.5 gallons per cycle
• Hopefully only three cycles per week would be required
• 3 cycles x 906.5 = 2,719.5 gallons per week (less rainfall due to rain sensor weather interrupt device)
• Watering of non-planted areas encourages weeds and more maintenance which increases labour costs
• Overspray onto roadway is an issue with the wind
• Not flexible to varied plant water requirements if varied plant material requiring different amounts of water is used

Ok, got that? A spray system would consume 2,719.5 gallons of water per week. Big deal, right? This system is fed from a stream that runs through Landscape Ontario’s property. The water is pumped and filtered, and then filtered again after the low-volume valves, before heading to the drip emitter. But, let’s say you are from one of the areas in Canada with a limited water supply, facing restrictions. Why are landscape irrigation systems restricted so readily? Because they tend to consume a lot of water. Some systems apply 1,500 to 2,000 gallons per watering cycle every second night, regardless of whether the plants need the water or not.

The subsurface alternative
Ok, so how good is a subsurface system in using water, compared to a conventional spray system? Not all spray systems are heavy water users – depending on the design and application. Let’s check the subsurface system out. Comprised of approximately four rows, 200 ft. long on each side of the island planter bed, with inline 1.0 gph emitters every foot.

• 4 x 200 x 2 =1600 ft. / 12 in. = 134 emitters (rounded up)
• 134 x 1.0 gph = 134 gph
• 134 gph /60 (divide gph by 60 to arrive at gpm) = 2.23 gpm
• 2.23 gpm x 10 mins. per cycle (once soil moisture content is at the level plants require) = 22.3 gallons of water per watering cycle
• 22.3 gpc (gallons per cycle) x three cycles per week = 66.9 gallons per week (less rainfall due to rain sensor weather interrupt device)
• Results in 66.9 gallons of water per week compared to 2,719.5 gallons for the spray system
• Water savings of 2,652.6 gallons of water per week, which when calculated for a 28-week irrigation season (typical in Southern Ontario) = 74,272.8 gallons not required.

Other advantages include less vandalism for the subsurface system, no wasted overthrow onto hardscapes, no stained fences, no rotted wood windows, fewer weeds due to water being contained right beside the plants and many more pluses.

The story and the numbers dramatically demonstrate why a low-volume subsurface system is the obvious choice. Do you think it’s time for you to try this application? Tread lightly with turf applications, as it is still unproven — but many are going subsurface even in turf. Be sure to use an air/vacuum relief valve which will expel air from lines, allowing for more even water distribution, preventing the system from turning into a vacuum when the water shuts off, sucking dirt into the emitters. The emitter is a tiny hole, so think small when creating low-volume drip systems. Let’s save some water, and show municipalities that irrigation done well can be a big water saver over most other means of watering plants.

Volunteers make the difference
Thanks to the volunteer members of the Landscape Ontario Irrigation sector group, especially Neil Whitehall from Watertight Home Services Irrigation Division and John Lamberink of Aquality Irrigation, and the irrigation equipment manufacturers and distributors who helped make this project possible. Thanks also to Rodnie Johnson of IPS and the other industry members who came to learn and help over a three-week period this spring.

The final installment of this article will highlight the Toro Precision H20 high pop-up spray system. Each article includes detailed descriptions and photos in the hope that readers will recognize the water savings from plant-specific precision irrigation systems, and demand such for your projects. Short video clips and lots of photos are available from me by email.

                    
Lorne Haveruk is an Ontario-based water resource consultant, irrigation designer, author, speaker and educator.