Tree Watering Bags: Are They Worth Using?

In the July issue of ISA Arboriculture & Urban Forestry magazine, Hossain, Stuhlinger, Olson, and Babst contributed, “A Comparison of Indirect Water Devices for Benefiting Newly Transplanted Urban Trees”. Urban trees often undergo a period of post-transplant stress which is exacerbated by a water-limited environment. Watering devices are available to help a newly-planted tree receive enough water by making the watering process easier and more efficient.

In the study, three types of watering devices were used to test their performance and applicability in watering a newly transplanted tree: upright bags, ring bags, and open tubs. Container-grown river birch (Betula nigra) were planted in well-drained compost and outfitted with one of the 3 watering devices. The experiment was conducted in a greenhouse to control for variations in natural precipitation, temperature, and soil.

Researchers found that there were no statistically significant differences regarding tree growth and health regardless of watering treatment, indicating that the watering devices provided no benefit to trees compared to direct watering (using a hose). A possible advantage to using watering devices is a reduction in water runoff due to their slow release approach. Future research should assess whether indirect watering systems can reduce the loss of water due to run-off.

Given the watering devices do not provide a tree growth or health benefit, what is the best use of your project budget when it comes to watering trees? Watering devices are easy to install and use, and their slow release approach may be beneficial in areas where water must be transported in. Plus, there is the added bonus of reducing operator time. As with any product, to have a benefit the product must be used – a watering device that never gets filled up does nothing, so ensuring an adequate operations and maintenance budget is paramount.

Selecting a watering device for your next project may benefit the trees if they are filled regularly, but the bottom line is that trees need water and will gladly soak it up any way they can get it. Direct watering, irrigation, or watering devices are all effective ways to get moisture into the soil – your site constraints and budget will dictate which you should choose.

Link to ISA publications list for original article (members only)

One comment

  1. There needs to be a huge caveat on this study based on the media the trees were grown in. “Container-grown river birch (Betula nigra) were planted in well-drained compost…” The purpose of Gatorbags and other water devices is to spread out the infiltration time in heavy or compacted soils where water is likely to runoff. If you can apply 15 gal of water in 1 or 2 min with a hose and not have water run off, then a watering bag will probably not provide any benefit. If, on the hand, spreading the infiltration out over several hours would eliminate runoff, then watering devices can help.

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