Water-Wise Strategies for Arborists

Sustainable Irrigation and Tree Health

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As climate change alters weather patterns, resulting in drier, hotter conditions, tree care professionals face twin dilemmas: trees suffering from reduced rainfall and local restrictions on water usage for irrigation.

To overcome both challenges, arborists need to adopt sustainable practices to conserve water while maintaining plant health.

Trees are integral to the natural water cycle, and a loss of tree cover can result in more soil evaporation, exacerbating drought conditions.

A healthy tree canopy absorbs storm water, reducing the number of pollutants washed into streams and rivers. Meanwhile, the leaves of the canopy also slow down how quickly rain reaches the forest floor, allowing the ground more time to absorb water.

For example, a USDA Forest Service study found that a 54% tree cover in a Pennsylvania watershed reduced storm water runoff by 11%.

Even when rainfall is abundant, practicing water conservation offers several benefits. Using less water — whether from municipal sources or pumped from onsite ponds — lowers costs for businesses or clients, as they pay less for water or diesel fuel to operate pumps.

Additionally, delivering the correct amount of water deeply into the soil ensures that trees are healthier and better equipped to withstand drought.

Water conservation practices such as monitoring soil moisture, understanding the water needs of different species, and applying mulch correctly all contribute to maintaining tree health.

Sustainable Water Practices

When designing a landscape from scratch, prioritizing sustainable water practices is key. Planting native trees that are acclimated to local rainfall patterns reduces the need for irrigation.

Grouping trees and plants with similar water needs further minimizes the risk of over- or under-watering. In areas exposed to intense sun or high winds that dry out soil, finding ways to mitigate these conditions or deciding not to plant trees in such locations may be necessary.

For existing tree plantings, several techniques and tools can help arborists conserve water.

For instance, the New Mexico State University Extension suggests that drip irrigation can save up to 70% of applied water compared to traditional sprinkler systems.

Zachary Hall, general manager of Millican Nurseries LLC in Chichester, NH, is a proponent of drip irrigation. He formerly served as the irrigation supervisor for the wholesale nursery and was responsible for irrigation for 16 years.

“When I first started, 75% of our material was watered with overhead sprinklers,” he said.   

Now, about three-quarters of the nursery is equipped with driplines with emitters going to tree root balls.   

“Spraying useless water to get things moist has been replaced with putting water directly into the root ball,” Hall explained. “It is more intensive to set up, but it does much better watering and we save a significant amount of water.”

Millican’s tree rows are 175 feet long, with four trees planted across, spaced five feet apart. Drip lines, or “spaghetti” lines, run between the rows with individual emitters for each tree.

These lines can be rolled up and out of the way when not in use, though the company replaces the hoses about once every decade due to wear and tear.

Despite the presence of a main weather station, five rainfall monitoring stations, and moisture sensors, Hall stated watering decisions are still made “primarily off of feel.”

Millican pumps irrigation water from ponds on its property, and most of the runoff returns to the holding ponds due to the topography. They’ve chosen not to implement an automated watering system due to the complexity of their setup.

“We have a 13,000-gallon system with a lot of hydrants, valves and moving parts,” Hall shared. “It’s better to have eyes on the system to know it’s running properly than to trust a computer.”

To conserve water further, Millican consolidates rows and moves trees as the selling season progresses, reducing the acreage that needs irrigation.

Additionally, drip irrigation helps the nursery sell healthier trees.

“Trees aren’t getting overhead water, so there’s no leaf spot, no blast off the leaves. So, the tree doesn’t look tired,” Hall noted. “The happier you can make the root ball, the better off you are.”

Water-Saving Tools and Techniques

While Hall prefers a hands-on approach, many professionals in tree care utilize automation tools to ensure proper watering.

Drip irrigation systems can be equipped with timers and controllers to operate on a preset schedule. Smart irrigation controllers, which use sensors to monitor soil moisture, can adjust watering schedules to prevent over- or under-watering.

However, setting up these systems requires upfront labor and costs, especially when installing emitter lines for each tree. The expenses should be weighed against the savings from reduced water usage and the benefits of delivering water directly to the root ball instead of using less efficient water sprinklers.

Mulching is another effective water conservation technique. Organic mulch helps reduce water evaporation from the soil, minimizing the need for frequent watering. It also improves soil structure as it decays. Arborists should apply mulch two to four inches thick, keeping it a couple inches away from the base of the tree.

The Quarterly Watering Plan

There is yet another option for conservative irrigation that is almost as hands-off as automated strategies.

TREEIB is the creator behind the reusable irrigation bag that delivers a lasting source of water to mature trees. The large bags are placed around the tree’s drip line which then provide slow, deep drip irrigation that encourages root system expansion.

Once placed, the bags are filled with water using a garden hose or even a fire hose. The heavy-duty, reusable 400-gallon bags release water over eight to 22 hours and are then removed from around the tree.

The company recommends watering trees four times a year: early spring, late spring, late summer, and autumn.

While the system wasn’t originally designed as a water conservation technique, it does save water.

According to Martin Tuser, chief researcher and business development director for TREEIB, the system encourages root growth and increases root biomass, allowing trees to absorb more water and reducing the frequency of watering.

Tuser’s tests on drought-stressed trees in the Czech Republic showed that four waterings a year restored tree health in just two to three years. The watering dose was 10 days of transpiration volume per application. Trees showed rapid primary and secondary growth, longer assimilation and improved fruiting.   

Little research has been published on the water needs of mature trees, he noted, and using the watering bags conserves water compared to the amounts called for in recommendations he found.   

In Salt Lake City Tuser works alongside his research partner Lynsey Nielson is the lead horticulturist at Red Butte Garden & Arboretum.

According to the pair, the general recommendation is to apply 20 gallons of water per inch of caliper once or twice a week, a seasonal volume that Tuser considers “enormous.”   

He suggested that watering mature trees provides greater environmental benefits with less water than would be required to replace a mature tree with hundreds of small trees.

For example, to get the cooling effect of one large tree, a city would have to plant about 600 small trees, which would require 500,000 liters (132,086 gallons) of water a year, compared to 24,000 liters (6,340 gallons) to keep the large tree healthy.

Tuser, who presented at the ISA conference in Atlanta, said tree care professionals have been buying the TREEIB bags because they solve the dilemma of how to get customers to properly water large trees.   

Arborists who buy the bags can rent them to customers or add a watering service to their portfolio, he explained.   

The bags are “a great supplemental method of tree care for trees that aren’t in good shape. Soil and tree injections require a skilled person and are invasive. Watering is not. TREEIB makes watering of big trees feasible,” he shared.

A large tree care company has evaluated the bags and “they reported it worked as advertised,” Tuser continued.

The bags, which come in two sizes, are being used in the United States, Canada, and Europe.

Future Trends and Emerging Technologies

Manufacturers are continuously improving irrigation technologies to promote plant health while reducing water usage.

For example, the Toro Company has introduced Transpira, a plant sensing technology that measures a tree’s water usage by monitoring sap flow in the xylem to provide data for more informed irrigation decisions.

Tony Tavares, marketing communications manager for Toro Ag Business, emphasized that this technology ensures trees receive the right amount of water.

“It’s not just about saving water; it’s about getting the right amount of water for a tree group,” Tavares explained.

Toro typically places Transpira sensors directly on three trees per block. Along with sap flow, Transpira considers environmental conditions and information about specific species of trees to suggest how much irrigation the block will need in the coming week.   

Currently, Toro is primarily focusing on Transpira usage with crops such as apples, tree nuts, citrus and avocados, but the technology can be used in arboriculture applications as well.   

According to Tavares, commercial landscapers buying hundreds of trees to be planted in blocks around a project could use the technology to monitor tree health and conserve water.

Meanwhile, nurseries could use the technology both to ensure their trees are getting the right amount of water and to gain knowledge about proper watering levels they can share with customers.   

Looking ahead, Tavares suggested that artificial intelligence (AI) could play a role in simplifying irrigation recommendations by analyzing data from tree sensors, onsite weather stations, and weather forecasts.

“AI can take a lot of data and simplify it to recommend how long to irrigate,” he said.

Water Regulations

In some regions, water conservation is not just encouraged — it is mandated.

For example, the California State Water Resources Control Board adopted new water conservation measures in July 2024, addressing the state’s projected 10% shortfall in water supply by 2040.

The new measure requires local water suppliers to incorporate water conservation through a variety of means, ranging from education and outreach to installing landscaping with low water needs.   

Even still, California regulation puts a priority on protecting trees. Water suppliers will be able to request a variance for irrigating existing trees, and the plan incentivizes planting new trees that are better suited to a drier climate.   

Conclusion

Arborists have many options for conserving water, ranging from manual techniques to advanced automated systems. Each situation may require a different solution, depending on factors such as cost, installation complexity, and ease of use.

Ultimately, adopting effective water conservation practices results in healthier trees, reduced water usage, and ecological benefits.