The Q&A Archives: soil ph

Question: I have a pin oak tree that has light green almost yellow leaves .I thougt that it was attractive,then I read it was not getting nitrogen because the soil ph was wrong. I have started using Miracid according to the directions.My question is there a faster way to add acid safely or is what I'm doing ok?

Answer: Pin oak (Quercus palustris) should do fine in a soil with a pH of about 5.0 to 6.5 at the highest. The soils in New York state are usually on the acidic side, so I am a little doubtful this would be the problem. An exception would be if the planting area has been limed heavily to raise the pH. I would strongly recommend you check the soil pH where the tree is planted to be sure that is truly the problem. You would not want to overacidify the soil as that too could be harmful.

If the soil needs to be acidified, the best approach would be to use aluminum sulfate to bring it down initially, then use sulfur as needed on an ongoing basis to maintain it. (Aluminum accumulated in excess over time can cause damage to the plant, so sulfur is better for longer term use.) You might also find that a slow release fertilizer for acid loving plants such as Hollytone is adequate. However, it is important to note that it is difficult to treat soil pH on an ongoing basis over a large area to accommodate the tree's spreading roots (well beyond the branches) and over its life span of decades. I can't stress enough how important it is to test and retest the soil over time to guide your efforts.

Chlorosis due to high pH will show a pattern of yellowing but with green veins remaining on the leaf. You might find the section "Culture" at the following page interesting in that regard.

I should also mention that the pale color could be due to something else such as poor rooting or constricted roots, encircling roots that have not expanded beyond the planting hole, lack of soil fertility or micronutrient deficiency, underwatering, or a pest or disease problem. Or, it can be related to chemical exposure such as lawn chemicals or herbicides used near the tree. For this reason I would strongly uggest you consult with your local Cornell county extension. They can help you with the soil testing and interpreting the results and can also help you trouble shoot the pale coloring on the tree.

In the meantime, if this is a new tree, it should be mulched with several inches of organic mulch (an acidic material such as pine bark might be helpful). Apply the mulch in a flat layer spread out under the tree to past the branch tips and do not allow it to touch the trunk or bark of the tree.

If this is a new tree, also be sure you are watering correctly. Over watering and under watering can both cause drooping or wilting or bad color due to root damage. Your goal in watering is to keep the soil evenly moist like a wrung out sponge, not sopping wet and not dried out. To know if you need to water, dig into the soil with your finger. If it is still damp, do not water yet. When you do water, apply it to the soil surface and water thoroughly and slowly so it soaks down to the deeper roots. After watering, wait a few hours and then dig down to see how far the water soaked in; it can be surprising.

There is no set schedule for watering, it depends on your soil type and on the weather. Using an organic mulch several inches thick over the root area will help reduce watering needs as well as feed the soil gradually as it breaks down over time.

Good luck with your pin oak!

« Click to go to the homepage

» Ask a question of your own

Q&A Library Searching Tips

  • When singular and plural spellings differ, as in peony and peonies, try both.
  • Search terms are not case sensitive.

Today's site banner is by mcash70 and is called "Moss on a log"