All the Ways We Water the Garden: Strategic and smart watering practices taken from UBC Botanical Garden

As gardeners, we’re always looking for ways of getting water to our plants more efficiently, with less hassle and in less time. And hopefully, using less water too. We’re going to take a peek ‘behind the curtain’ here at UBC Botanical Garden and show you some of our irrigation systems (we use many of the systems available on the market) and share some our strategies for being more efficient with less hassle (yes, we still have to drag out hoses too), and in less time (more on time later. It’s an important one).

This isn’t a comprehensive how-to on irrigation, or a water savings manual. You can read it more like a buffet, picking and choosing some of the key takeaways that apply to your specific garden and situation. After all, UBC Botanical Garden is a collection of smaller gardens, each with its own distinct character, microclimate, and plant palette, and chances are you’ll find something that applies to you as well.

The Front Entrance and Roseline Sturdy Amphitheatre

The front entrance to the garden is a logical place to start. Scott Ferguson has recently taken on the care and maintenance of the front entrance from Chris Bale (Chris now manages the Roseline Sturdy Amphitheatre and adjacent areas). Hoses play an important role here for areas without permanently installed irrigation.

Soaker hoses snake through the garden islands and in the driveway near the main gate, and can be easily connected/disconnected to the water source. Some benefits of a soaker hose are that they are inexpensive, simple enough for a home owner to install, and don’t require underground installation. Water is emitted along the length of the line and soaks into the surrounding area; it is especially useful for hedges. A word of caution for cheaper soakers hoses: they clog easily, so go for quality.

The hoses also connect to other areas at the front entrance. The oscillating sprinkler, a classic tool that never goes out a style, is used for a new area with turf alternatives and the tall impact head sprinkler showers the visitor-favourite wildflowers in the parking lot meridian. There’s no doubt about it, dragging hoses to those hard to reach places takes time. Scott’s logic on saving time is this: he’d rather set up a hose in one area and spend time watering longer and deeper than on shorter intervals multiple times a week.

Over in the Roseline Sturdy Amphitheatre and surrounding areas, irrigation has been installed underground. In the garden as well in the terraced lawn areas of the amphitheatre, there are pop up sprinklers (see picture to the right). Using interchangeable nozzles, these sprinklers can spray a radius of 1.5-4.5 m (5-15’) and are generally used for smaller lawn areas, garden beds, and ground cover areas.

The lawn needs the water, but many of the beds flanking the lawn are filled with a colourful array of drought tolerant species from the Mediterranean region. Do they really need the water, as well? Isn’t sourcing plants that require minimal watering where we’re headed to in the future? It very much is at the forefront of the nursery trade and horticulturists’ minds. But Scott made a subtle point: many plants in this section would survive just fine, but to flower and look their best, they require the odd supplemental soak. For botanical gardens and public parks, water will be a continual need in order to showcase beautiful displays for visitors and guests.

Key takeaways from this area:

• If you’re going to the effort of dragging out hoses, water deeply and less often.
• Soaker hoses are an efficient and economical option for homeowners

North American Gardens

The North American collection comprises the BC Rainforest Garden, Carolinian Forest Garden, Garry Oak Meadow & Woodland Garden, and Pacific Slope Garden. Out of all those gardens, only one has an installed irrigation system. An impact sprinkler (pictured on the left) is the typical sprinkler you’d find when strolling through the Carolinian Forest.

Shadier than either the front entrance or the Roseline Sturdy Amphitheatre, the Carolinian Forest Garden is filled with young tree specimens from eastern North America: ashes, oaks, sassafras, redbuds, magnolias, and maples. Water evaporates under these shady conditions much more slowly than in full sun exposure, but there are also other factors at play that contribute to maximizing infiltration and minimizing water evaporating. The forest floor under the canopy is mulched with arborist wood chips, natural leaf fall, twigs, even thick branches. Beyond the water benefits, mulch is such an incredible multi-tool: it suppresses weeds, reduces root compaction, benefits soil biodiversity, and moderates temperature extremes.

I talk about curator Ben Stormes’ approach to irrigation in this area to Horticulture Training Program students because it’s so intelligent. Ben grew up in Ontario and knows that summer rainstorms can drop a good inch in an hour. He brings those Ontario rainstorms artificially into the Carolinian Forest, turning on the irrigation for hours at a time or piggybacking off a lighter summer rainfall. Once again, using the strategy of watering less frequently but deeply.

The Garry Oak Meadow & Woodland Garden is modelled on a western Canadian rain-shadow ecosystem, which is a vastly different space. It does not have irrigation and requires manually setting up hoses with sprinklers. However, once it has finished blooming after a steady amount of rain in the spring, the plants are already headed into dormancy. Bursting with camas, sea blush and shooting stars, this garden should be on every visitor’s April/May must-see list. But by August, the area leaves visitors wondering if everything has died. Despite appearances, this is all part of its natural seasonal cycle.

“Even for a naturalistic garden, there is a stronger emphasis on garden.” – Ben Stormes, Curator

Beyond any particular area, Ben also talked about the importance of watering newer plantings: a new seedling, a potted plant being planted into the garden, or even a transplanted shrub from one area to another. What these scenarios have in common is that the root system is not yet established. Until an individual plant has a thriving root system to draw up water, it’s going to need regular watering, usually for the first one or two seasons.

Native plants are often touted as being more drought tolerant simply because they are naturally adapted to the region’s seasonal weather patterns. This may be true once they are established (some natives are poorly adapted to garden situations), but because we’re in a garden setting, we want to set our plants up for success. In nature, one in a hundred seedlings may survive a summer without water. Our garden wants better odds than that. Ben says, “Even for a naturalistic garden there’s a stronger emphasis on garden.”

Key takeaways from this area:

• Water plants until they are well established. This includes new seedlings, native plants, drought tolerant plants, and those newly planted/transplanted
• Mulch helps water infiltrate more easily and slows the loss of water through evaporation

The Food Garden

Sometimes, food gardens can become more functional than beautiful, but Linda Layne combines both in the Food Garden, creating a captivating edible exhibit. The irrigation system highlighted here is very different from the rest. For starters, the larger impact heads and pop up sprinklers we have touched on have manufacturer data sheets that list range, water output, etc. All of the systems covered so far give statistics in gallons per minute or GPM. In contrast, the output of the micro irigation system set up in the raised wooden planters in the Food Garden is measured in gallons per hour. This is no small detail.

Micro-irrigation is a catch-all term to describe irrigation systems that either drip slowly along perforations in a tube (similar to a soaker hose, but at wider spacing) or have tiny sprinkler heads (see picture to the top left or bottom right). The sprinkler heads vary by manufactuer, but these particular ones can spray in patterns 90, 180, or 360 degrees.

Micro-irrigation has increased in popularity in recent years and is used across multiple sectors: in greenhouses, agriculture, vineyards, and green walls. The emitters are precise with their water distribution and the black polyethelyne tubing is flexible and a superior environmental alternative to PVC pipe. Overall, micro-irrigation is easy to install and maintain compared to conventional irrigation systems, making it very attractive to homeowners and hobby gardeners.
Linda has timers set on each of the zones in the Food Garden and prefers to have the micro-sprinklers go off by the time she arrives in the Garden at 7:30 a.m. That way, she can walk through and see if there are any problems with the system: a sprinkler head twisted around and spraying into the path, a puncture in the tube gushing water, or a blocked spray due to new growth.

Having timers on an irrigation system is huge advantage to any system, micro-irrigation or not: the early hours of the morning from 4:00 a.m. to 8:00 a.m. is generally the best time to water any part of the garden and that is earlier than anyone of us would like get out of bed and manually water our gardens. While the early morning hours work for the summer when the sun is at its most intense, come late summer/early fall, when the squashes, zucchini, and pumpkins are coming into their own, the irrigation timer has to be adjusted again. Powdery mildew is one example that Linda cited for starting the timer later in the morning—at 9:30 a.m.—so that the later rising sun can dry out the excess moisture on the leaves. Extra moisture is what powdery mildew thrives on, so keeping the leaves dry while still giving the plant the water it needs is key.

Timers are a great labour saving device—cost effective ones can be picked up a hardware stores and easily installed onto hoses or soaker hoses—but they still need to be programmed. Plants don’t water themselves; intelligent watering takes into consideration the time of year and types of plants being grown.

Key takeaways from this area:

• In summer, water in the early hours of the morning
• You can be strategic and adjust your irrigation for earlier or later start times during the season
• If it’s appropriate for your garden, consider switching to micro-irrigation for your garden. It’s cheaper to install, easy to maintain, and the water savings are enormous

The Alpine Garden

The E.H. Lohbrunner Alpine Garden is a southwest facing garden that is home to montane plants from around the globe. There is always something in bloom no matter the time of year, but this particular space poses its own unique challenges. Curator Laura Caddy sums it up: “I’m watering hydrophobic soil on a slope.”

A hydrophobic soil is one that repels water (hydro = water + phobic = aversion). Gardeners will have seen this when the soil is so overly dry that water runs off the soil surface. Those who have gardens built on steep slopes know the challenge of overland runoff and low infiltration rates. These can contribute to soil erosion and long-term destabilization of the embankment. Meanwhile, plants still go thirsty because the water has never penetrated deep enough to reach the roots.

 

“I’m watering hydrophobic soil on a slope.”- Laura Caddy, Curator

One strategy to combat both of these problems is to do a ‘priming’ cycle. This means watering for a short period of time and then doing a longer cycle the second time around. For Laura’s system, the gap between first and second watering cycles is about 30 minutes. The first pass moistens the soil surface enough to allow absorption by the second irrigation by the time it runs through all the zones. Although the use of this priming cycle is most relevant to this section of the garden, most staff cited this as a useful technique in other garden areas, as well.

Laura also uses rain gauges in her section to make sure irrigation levels are reaching 20 mm (0.8”) of combined precipitation and irrigation per week. A rain gauge is a simple, useful tool in any garden. For instance, the recommended amount for both lawn areas and vegetable gardens is between 25 mm-38 mm (1-1.5”) of water per week. Periodically putting out a rain gauge to make sure you’re reaching your target, neither under or overwatering, will give you confidence.

Key takeaways from this area:

• Do a priming cycle to get the soil moist before returning to do a second round. If you have an irrigation system on a timer, you can set it up as a second start time. If you’re hand watering, you can do a pass around the garden before starting at the beginning again.
• Know the water requirements of the plants you are growing in a particular area and use a rain gauge to make sure you’re meeting your watering target.

The Asian Garden

The irrigation system of the David C. Lam Asian Garden will be our last system we look at. This is the largest garden section as well as the oldest; the collections are nestled among second growth native conifers and understory plants. Dappled sunlight and deep shade dominate this area with a few sunny open meadows.
An irrigation system of sorts had been cobbled together over 30 years with different irrigation parts: a pipe extension here, a irrigation head added there. It became a sprawling, logistical headache. Water pressure was a constant issue. Sprinklers were on most of the day in order to ensure coverage, but that interferred with visitors’ experience of the garden. Inevitably, someone would be wandering through a side path when the sprinklers would suddenly sputter into life! In 2018, donor funding allowed the system to be redesigned and rebuilt from scratch.

The new irrigation system objectives included creating a permanent, efficient, programmable irrigation system with a long operational lifespan, capacity for anticipated future expansion and demand for supply. Over 1.5 km (you read that right!) of HDPE (High Density Polyethylene) pipe was installed with 90-mm (4-inch) diamater main lines branching off into 50-mm (2-inch) lateral lines. There are 18 valve boxes distributed throughout the garden, but since they are below ground, you’re more likely to notice the accompanying pedestals, which house the irigation’s electrical system. It’s the only centralized system in the garden, a far cry from the Macgyvered sprinkler days.

As for the sprinklers themselves, overhead rotary heads were chosen as they can produce uniform coverage. For range, most of these rotary heads have a radius of 11 m and others have a shorter distance of 6.5 m (in feet, that would be 21-36 ft). In the image to the left, you’ll notice the rotary sprinkler head is set above the foliage. Andy Hill, curator of the Asian Garden, pointed this out as we walked along Lower Asian Way: “You have to set your sprinkler heads above your highest permanent groundcover. For this area, sword fern is the forest groundcover so that was our default height.” This is to avoid blocking the spray of water coming from the sprinkler heads.

On a related topic of obstructions, traditionally for any irrigation system, there is overlap of sprinkler heads to ensure adequate coverage. But this is far easier in an open area rather than one with multiple obstructions, like trees and shrubs. These obstructions create a shadow effect where the water cannot reach beyond the obstruction, creating dry spots. This was a big challenge in the design process since the Asian Garden has a large number of trees and larger shrubs in the collection and obstructions had to be assessed on the ground during sprinkler placement.

This is easier to do when building it, but once installed and a garden is established, this takes creativity in troubleshooting. When your spray is blocked, there are choices: can you prune the obstruction in such a way to let the water in? Would it be better to take the obstruction out altogether? Or would adding another sprinkler be the simplest solution? This is at the heart of gardening: it never stays the same, it is always changing. Our water practices needs to adjust and adapt too as our garden matures. Even with a state-of-the-art centralized irrigation system.

Key takeaways from this area:

• Do a cost-benefit analysis on whether a well-planned out, centralized system or multiple irrigation systems will be more efficient for your garden space over the long term
• Set your sprinklers above the highest permanent groundcover
• Consider the spaces in your garden where there are obstructions and the dry spots behind them