![]() Note the differences in where the roots are! Source: Chan et al 2002. From the left, the first and third trees received supplemental irrigation while the second and fourth did not. Could that cause problems when you stop nurturing them? Take a look at the root profiles (below) of some three-year-old trees that were part of an experiment. Perhaps that encourages more fine roots to persist in those upper few inches of soil, rather than developing more deeply where moisture remains longer into the season. As the upper inches of soil dry out in the summer, I sort of wonder whether replenishing their moisture is beneficial to a new seedling or not. They produce fine roots mostly in the upper 8 inches of mineral soil, and any organic material on the soil surface acts as a sort of buffer or mulch. I’ll go back to my earlier point that Douglas-fir trees are adapted to dry summers. Dang, I should have done a few more repetitions! So I can’t really compare the difference between the two. In the fast-watered spot, I could only get down about four inches, but there turned out to be a lot of buried bark in that spot, so that limited the probe. In the slow-watered spot, I brought up eight inches of evenly moistened soil. As expected, the entire soil profile that I was able to collect was moist. Two hours later, I probed the soil in the two watered locations. The soil core from a spot that got a quart of water as a slow drip. I know this happens when I water my yard, and for landscape trees, it’s always recommended to water slowly, deeply and infrequently. ![]() I thought that maybe delivering the water slowly would allow it to penetrate more deeply, whereas pouring the water might cause it to run off. In the other, I just poured the water directly onto the ground. Then I set out my two yogurt tubs in different bare spots, but in one, I punched a small hole in the bottom to allow the quart of water to seep out gradually. The soil core from unwatered soil, showing that the bottom few inches were still moist in July. A month from now, it may be a different story. So by early July, the soil still had good moisture for the seedlings’ fine roots to access. The first two to three inches were dry, but below that the soil was cool and moist. I took a soil sample with my probe in a bare spot near a seedling. Watering in these conditions would defeat the purpose, as you would be watering the weeds too. The first thing to note are the weedy annuals surrounding the seedlings, a common condition two summers after planting. My intention was to see how different methods of watering affected the soil moisture profile. ![]() I brought a soil probe, a jug of water, and a couple of quart-sized containers (i.e. I decided to try a small, highly non-scientific experiment to help shed light on this question, so I went out to a nearby clearcut that had been replanted last year. So, suppose you planted a reasonably small number of trees, and they are easily accessible (on flattish ground, near a road), and you have some method of getting water to the site (a water tank, a hose, etc.) These conditions could make watering feasible, so for the woodland owner who wants to give their baby trees the best start in life, or who just has a micromanager personality type, is it worth the time and effort? In light of these factors it doesn’t seem like an unreasonable question. Scientists predict that summers in the Pacific Northwest are only going to get hotter and drier in the future. After all, all signs are pointing another drought year. And, I know one or two woodland owners who have watered trees that they were concerned about, only to have them die anyway.īut this year, after fielding the question of watering young trees again, I started to think a little more about my standard answer. After all, millions of Douglas-fir trees are planted each year in Oregon, and most of them make it without any supplemental water. ![]() I also point out that our Douglas-fir trees are adapted to withstand dry summers. Of course, in most cases, it’s not even a practical consideration, because the logistical challenges of delivering water to hundreds, if not thousands of seedlings on steep or rough terrain far from any water source far outweigh any potential benefits. ![]() Often around this time of year, I’ll get a question from a small woodland owner asking whether it’s worth the trouble to try to water their newly planted tree seedlings. By Amy Grotta, OSU Forestry & Natural Resources Extension – Columbia, Washington & Yamhill Counties ![]()
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