Asked on Apr 12, 2012

Will many shrubs survive if planted in soil with a pH of 4.8?

This is obviously quite a scientific question. We installed a fairly large number of plants in t backyard about 3.5 years ago. I met with the homeowners today to look at their frontyard projects. While there, we were looking at the condition of the backyard plants. Most of the plants look to be almost the exact same size as the day we installed them. All of the shrubs are on a drip irrigation system, which the homeowners have dutifully monitored. We even installed a 1100 gallon rain harvest system that they used during the water restriction times.
On the sunny side of the yard, we installed 3 Knock-Out roses, which they say have never been pruned. The roses are less than 3 feet tall.
In the shady areas there are groupings of azaleas, anise, Shasta viburnum, fothergilla, buckeye, cephalotaxus, oakleaf hydrangeas, daphne, and a few other plants.
The oakleafs are the happiest of the plants, but still fairly small after 3.5 years. 100% of the anise are dead. While there with them, I pulled up photos of their installation taken at completion of the install, and there was almost no change in size.
The homeowners then mentioned that they had soil test results in a file. When she brought them out, one section that was tested in the middle of the backyard showed a pH of 4.8. I know that certain plants enjoy acidic soils, but 4.8 is the lowest that I have ever seen.
Would this very low pH be a possible reason for the very poor performance of their investment in their landscape? As we do with all of our clients, I want to figure out what is going on and help to correct any issues so that their backyard will flourish and grow.
Thanks for any advice or ideas.
  9 answers
  • 3po3 3po3 on Apr 12, 2012
    I'm pretty sure you know more about all this than I do, but my understanding is that acid soils keep plants from absorbing and using nutrients, so it could be the problem with lack of growth. It's easy enough to correct, and it couldn't hurt to add lime or otherwise boost the pH.

  • Southern Trillium LLC Southern Trillium LLC on Apr 12, 2012
    Steve, you are correct about the root absorption, but many of the plants should do fine with a pH level of low 5. I also just remembered the we noticed the Shasta Viburnum and Itea are all dead. They said they were living last year before the leaves dropped but I see no sign of even a single leaf bud forming on any of the shrubs. It is always tough to be presented with a situation that is new and to have no good answer. But it does make me want to do more research and figure out the problem.

  • Douglas Hunt Douglas Hunt on Apr 13, 2012
    In Florida, soils with a pH as low as 4 are known, although rare. One of the issues of a low pH is that the solubility of some minerals (particularly aluminum) may increase to levels that are actually toxic to plants.

  • Walter Reeves Walter Reeves on Apr 13, 2012
    I think Doug's answer is closest. Aluminum toxicity from low pH.

  • Southern Trillium LLC Southern Trillium LLC on Apr 13, 2012
    Thanks Doug and Walter. I figured while meeting with the clients that with such a low pH, it was causing the major problems. The homeowners did pose the question regarding what will be the solution to such a problem. She said she did not want to be spreading lime or other materials over the yard constantly. Having never dealt with a soil pH this low, any ideas on how to best raise it? We cannot till in the soil due to the tree roots from all the surrounding hardwoods. If Lime is added, does it require annual upkeep and testing to maintain a higher pH? They have a chemical maintenance company that treats the lawns, and has looked at the shrubs before, but they never did anything to adjust the pH of the soil either. Today, I am going to take 3 more soil samples from different locations in the yard and send those in for more current results from exact locations. But the homeowners are still wanting to know how to best improve the conditions. Thanks for the help.

  • Douglas Hunt Douglas Hunt on Apr 14, 2012
    It's easier to raise pH than lower it. But I do believe lime needs to be worked in to the soil because it doesn't move into the soil the way a soluble fertilizer would. If they have wood stove or fireplace ash they could spread that on the beds as well.

  • Ken H Ken H on Dec 28, 2012
    Check out this link from a university study:

  • Ken H Ken H on Dec 28, 2012
    I live in Florida when I had troubles with my newly planted roses I used a sulfer additive to get the soil PH at a much better level. As the PH gets acidic (sandy soil, lots of rain) the roses need to have the PH adjusted again.

  • Elle Elle on Dec 28, 2012
    The low pH affects whether and what nutrients can be accessed by plants. Before you start adding things to change the soil pH, contact your county extension agent who can advice you on proper amounts of lime, etc. Also speak with a county Master Gardener who is familiar with local growing conditions and plants: A word of caution: my dad ruined my mother's veggie garden by adding lime. Don't amend soil unless you know how and how much!