How do I water my new trees?
Believe it or not, there is more to watering a tree than simply spraying it with a hose once in a while. Properly watering a tree will ensure that the tree establishes well at its new location, developing strong, deep roots that will sustain it through periods of drought as it matures. Please note that this article will not deal with how to properly plant a tree, although how the tree is planted does influence how water enters into the root zone.
First of all, you need to know what type of soil you have. In central Ohio, heavy clay soils are most common, and almost guaranteed if you live in a newer housing development where the soil structure is far from normal due to common construction practices. If you happen to have a sandier soil than commonly found in Ohio, you will need to adjust your watering accordingly.
A few things to keep in mind:
1. Roots grow where there is water and oxygen
2. Roots, and therefore trees, do best when moisture levels remain constant. Moisture does not mean saturation.
3. When you water a tree, water will infiltrate the soil, percolating through the soil profile as it drains through. This drainage is essential for proper oxygen levels to remain in the soil.
Newly planted trees lost a large part of their root zone when they were dug at the nursery to bring them to your landscape. Because of this, maintaining proper moisture levels is essential. As we want to encourage deep root growth, we need to get the water down to the bottom of the root ball. To do this, slow watering is required to allow the water to soak into the soil without running off.
The method I prefer is using a soaker hose looped around the root zone of the tree. I monitor moisture levels every couple of days and run the soaker hose for a couple of hours if needed. More for larger trees. In cooler weather, such as spring and fall, watering will be less frequent. In hot, dry summer weather, watering will be more frequent. I hesitate to tell folks to water "every 2-3 days" or "once per week" because I don't want to add water when it is not needed. Such rules of thumb are not necessarily bad, because at least regular watering takes place, but monitoring moisture has worked well for me.
Run your soaker hose until you are sure the soil is saturated. Then do not water until the soil begins to feel dry to the touch. Don't wait until it is bone dry before you water again, just seek to maintain decent moisture. The cycle we want to maintain is one of saturation, drainage and beginning to dry out before beginning the cycle again.
Why not water a little bit every day? Isn't this the same? The answer is no. Watering a little each day only waters the surface roots. The tree will survive, but may not establish roots down deep where it can find moisture during droughts once it has established and you will probably not be watering daily. For this reason I do not recommend counting on a lawn sprinkler system to sufficiently water a new tree. Go with the soaker hose method or use those green bags and make sure you fill them as needed.
You should water as described for the first three seasons, and then as needed after that. It is easy to forget to begin watering in the spring. Some springs are drier than others, so don't forget to start checking moisture early. I also continue watering in the fall after the leaves have dropped (if the tree is deciduous) because there is a period of root growth between leaf drop and true dormancy that I want to help along as much as possible. A tree going into winter dormancy under drought stress will not make it through the winter very well.
Remember: slow, deep, infrequent watering does the trick. Allow the soil to drain and begin to dry before watering again. If your site is poorly drained, keep in mind the bottom of the root ball will dry more slowly than the top. We do not want to keep the roots waterlogged as this will kill the tree.
Generally, if there has been 1"- 1.5" of rain per week you will not have to water unless your tree is planted in a place where water runs off too quickly to infiltrate the soil.
Remember, you can always call the office and ask for the Certified Arborist who serves your area if you have any further questions about planting or watering.
Thanks and good luck!
Your friendly neighborhood arborist,
José Fernández