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Fill ‘er up!


This water bag slowly releases 20 gallons over 8 to 10 hours.

Q.  What drinks 20 gallons at a time? 

A.   A newly planted tree. 

So, “fill ‘er up!”

Watering is essential to sustain newly planted trees until their roots are well established. The best way to water a tree is to let the water soak in slowly and deeply, to encourage the roots to grow down, rather than staying near the surface.  

Properly watering many street trees each week can be a challenge. One way to do this efficiently is using water bags. Each bag holds 20 gallons which is slowly released and soaks into the ground over a period of eight to ten hours.

The Urban Foresters of the Seattle Department of Transportation have 1,616 city-owned street trees to water once a week this summer, using  three 3,000-gallon tanker trucks, each with one driver and one “filler-upper.”  Beginning early this month, water bags were placed around the base of each new tree, and by late June, the crews will begin making their rounds, working 10 hours a day, four days a week. There are an additional 800 trees that may need supplemental water later in the summer and will be added to the routes.

Using watering bags is an efficient way to water a large number of trees.

When new trees are transported for planting, a portion of the roots have been trimmed off to form a root ball. Before it grows out and becomes well established, this reduced root system is not sufficient to collect the amount of water the tree needs during the summer growing season. Supplemental water is even more important for a larger tree, which needs more water. A rule of thumb is that a one-inch diameter tree needs supplemental water for one year after it is planted, a two-inch diameter tree for two years, and so on.
How much supplemental water does a tree need? A tree with a one-inch diameter trunk needs about five gallons a week to survive, and more to thrive. On the other hand, too much water too frequently can hurt a tree by preventing enough air from getting to the roots.
Home owners may also care for their new trees using water bags which are available at some hardware and garden stores. Other available devices are “watering rings” and “watering stakes”. Perhaps the lowest-cost method for watering a limited number of trees is to take an old five-gallon bucket and make a small (1/8-inch) hole in the side near the bottom. Enter a cotter pin in the hole, place the bucket near the base of a tree, and fill it with water. When all of the water has dripped out, the bucket can be moved to the next tree.

There is more information about watering new trees on SDOT’s Web site.

Now, if you see a green bag around the base of a street-tree, you’ll know what it is.  If it is empty, that doesn’t mean it’s not doing its job. It has probably already released its 20-gallons or so for the week, and is waiting for the next week when the crews will “fill ‘er up.”

Once established, many trees will not need supplemental water.