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Having trouble maintaining low Ph with container blueberries

Posted by container_blueberry (My Page) on
Tue, Oct 6, 09 at 13:47

Two months ago I bought several varities of Blueberry plants. Most of them were in #1 containers.

Since then I have re-potted the majority of them into #3 containers using 50% peat moss and 50% EB stone Acid loving plant potting mix (with some soil sulfur and EB stone acid loving plant organic fertilizer thrown in.)

Initially my ph readings came out around 5.0-5.5 but now after some heavy daily watering my Ph reading are around 7.

What should I do? I haven't watered for a week since the temperatures here in Northern California have dropped.

Will the soil sulfur eventually kick in as the microbials in the soiless potting mix increase?

Follow-Up Postings:

RE: Having trouble maintaining low Ph with container blueberries

  • Posted by tapla z5b-6a MI (My Page) on
    Tue, Oct 6, 09 at 14:08

My suggestion is to worry more about where soil solution pH is as a generality and less about chasing a particular medium pH, which I'm absolutely sure will end in frustration anyway.

If you use a fertilizer that derives its N from urea (not nitrates) and neutralize your irrigation water's alkalinity with vinegar if you suspect or know alkalinity is high, you'll be just fine. Container media pH is nowhere near the issue that the pH of mineral soils is.

From something I left on another post: BBs have some pretty unique nutritional requirements compared to most other plants. They grow in acidic soils where fertility is usually quite low. Also, the predominant form of available nitrogen (ammonium) is usually present at levels that could be toxic to many plants. However, BBs have mechanisms to cope with the acidic, ammonium-rich, nutrient-poor conditions. They form a symbiotic relationship with certain fungi, which derive carbohydrates from the inner portions of the BB root system, and in return, help extract nutrients (especially phosphorus and nitrogen) from the soil for the plant. So, in comparison with many other plants, BBs have very low nutritional requirements. In fact, they can be quite sensitive to high levels of some nutrients, and a heavy fertilizer application can injure them, so be sure you fertilize at reduced recommended strengths (1/4 - 1/2 strength, weekly to bi-weekly).

BBs also have the unique ability to directly absorb ammonium ions. Most plants absorb N in nitrate form, which is then converted to ammonium by a metabolic process before being incorporated into proteins. However, nitrate fertilizers can be harmful to BBs. For this reason, ammonium forms of fertilizer are recommended, such as ammonium sulfate or urea. Ammonium sulfate is particularly good because it acidifies the soil, and most soils tend to have a pH higher than 4.5. (Foliage-Pro 9-3-6 offers 2/3 of its N in nitrate form, which is normally a good thing, but not particularly desirable for BBs.)

In another thread, someone made the comment that there is no Ca in fertilizers for acid-loving plants because they don't like it. JaG appropriately pointed out that ALL plants need Ca, which is true. The reason there is no Ca in most of the fertilizers we use on container plants is simply because of solubility issues.

The fact that different species of plants tend to grow on different types of soil does not mean that the one needs more of a certain nutrient than the other. It just means that the plants have developed strategies to adapt to certain conditions.

Acid-loving plants have adapted to acid soils. Their need for calcium is still the same as any other plant, and their nutrient requirements do not differ from plants that thrive in alkaline soils. The problem for acid-loving plants is that they have not developed a method to limit their calcium uptake, and will absorb too much of it when available, resulting in cellular pH-values that are too high. Some acid-loving plants also have difficulties absorbing iron, which is tightly bound in alkaline soils, another reason why they thrive in low pH soils. This all pertains to the plants ability to handle nutrients, not to the actual nutrient needs of the plant.

Filix is concerned (remember, this is off topic slightly because it was addressing issues being discussed on another thread)about micro-nutrient availability if he uses the MG 30-10-10. It contains all the micro-nutrients that are likely to be deficient in container soils, but glaringly absent are the secondary macro-nutrients Ca and Mg ... S as well is missing. Supplying the Ca with gypsum and the Mg with Epsom salts is probably the best plan. Though insoluble, enough S can be had by including a tsp of elemental S per gallon of soil.


RE: Having trouble maintaining low Ph with container blueberries

Thank you for the good advice. Soil solution ph > medium ph makes sense to me.

How much vinegar can be added to my 2 gallon watering can?

Is there any type of vinegar I should avoid?

Incidentally I noticed vinegar has been used in other scenarios for helping certain types of bacteria to grow faster. I wonder if this would have any effect on the type of bacteria that convert soil sulfur to sulfuric acid? Or maybe this type of bacteria is unrelated?

RE: Having trouble maintaining low Ph with container blueberries

  • Posted by tapla z5b-6a MI (My Page) on
    Tue, Oct 6, 09 at 18:37

How much vinegar depends on how alkaline your water is. You can safely add an ounce to a gallon of tap water for your BBs. Use white vinegar - it's cheap. I'm not sure what effect the vinegar would have on bacteria. I never went looking to find out because I don't think it's important.

Good luck.


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