What are Tree Watering Bags?

Tree watering Bag. Photo: www.treegator.com

You’ve probably seen them on young trees planted by your municipality and maybe you wondered what they were. They usually look like a tall brown, green or black soft plastic pyramid placed around the trunk of a newly planted tree. If so, they’ll likely be called tree watering bags or tree bags.

Sometimes though they’re like a plastic doughnut that fits around the base of the tree, in which case you can expect them to be called tree rings or tree watering rings. 

Designed to Moisten

And of course, the word “watering” gives away the whole story: they’re designed to water young trees during the critical early period after they are first planted. The bag or ring releases water slowly through tiny perforations, so it keeps the root ball evenly moist while the tree settles in, helping to prevent transplant shock and drought stress.

Most tree bags hold 20 gallons (75 liters) of water, enough for a typical young tree. Tree rings vary from 5 to 32 gallons (19 to 121 liters). Expect to pay some $20 per bag.

Municipalities like them, because they don’t have to send out staff to water newly planted trees two or three times a week if the weather is hot and dry. And filling a tree bag/ring takes less time than a thorough watering. But home gardeners also find them handy, especially if you’re not home often enough to hand water. Or if you’re just plain lazy (I certainly have no problems with that!)

How to Use a Tree Bag

The idea is certainly simple enough.

First, wrap the bag around the base of the tree, placing it directly on top of the mulch. The surface needs to be fairly level for the bag to drain properly.

Most models have a zipper so you can simply zip the two sides together from the base to the top so it hugs the trunk.

If it’s a larger tree with a thick trunk, say 3 to 4 inches (7.5 to 10 cm) in diameter, use two bags and zip them together.

Now insert a hose into the opening at the top of the bag and start filling with water. As it fills, lift occasionally to remove any folds so the bag fills out entirely. You can add a dilute fertilizer to the water if you want, although modern arborists no longer recommend using starter fertilizers on young trees.

Fill to capacity, remove the hose and close the opening if there is a flap or plug provided for that purpose.

Most will drain slowly over a 5 to 9-hour period.

In most cases, this will keep the soil evenly moist for 5 to 7 days, then you refill it. 

For small trees, you would usually keep the tree bag active for the entire first season, spring through fall. On larger caliper trees, which often have a harder time settling in, or any tree that seems to be struggling, a second season of slow watering may be necessary.

Obviously, you can use tree bags again and again. Just drain well before you store them for future use. 

Check on the product’s label to see if it can stored in below-freezing temperatures. Many do need to be brought into a frost-free spot for the winter.

Tree Rings

Tree rings are used in a similar fashion, although there’s no zipper. However, they’re lower and wider than tree bags, so need more horizontal space, up to about 40 inches (1 m). Also, since they are only about 6 inches (15 cm) high, they can also be used on shrubs with multiple branches at the base rather than a single trunk.

So Far, So Good

These tree bags are good for busy parks departments and neglectful gardeners. They save considerably on water usage as well and help prevent over and underwatering. Also, they keep the soil cooler, a boon to young tree roots in hot summer climates.

The Downside

Handy though they may be, tree bags and rings aren’t perfect.

First, they often don’t hold enough water for larger caliper trees, although, as mentioned above, some models can be doubled up to help cope with this problem.

And you also have to remove them from around the trees and drain them for the winter, even if you’ll be using them on the same tree for a second season, so that’s an extra step.

Thirdly, watering just around the trunk isn’t ideal. It would be better to water thoroughly out beyond the original root ball and out to the dripline to encourage roots to spread normally, that is, in an outward direction. This will help prevent girdling (when tree roots wrap around the trunk and strangle the tree). In clay or loamy soils, the tree bag may be able to compensate for that flaw to a certain degree, as moisture tends to spread out as well as down, but it won’t in sandy soils, where water just goes down. Again, this is going to be more of a problem on large caliper trees. 

On the other hand, if you’re not going to be around to water more carefully, certainly a tree bag is better than letting a young tree’s roots dry out!

And some gardeners tend to forget to water when there’s a tree bag or ring sitting out in plain view, looking as if it’s doing something important. You just have to remember that these tools do need some maintenance and therefore that watering every 5 to 7 days will still be necessary. 

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Tree watering bags and tree watering rings: they may be just what you need to add to your arsenal of tree care products.