Adjusting PH Levels for Blueberries in Containers

lawanddisorder(6)April 8, 2014

I have a number of blueberry plants that I planted a year ago. At that time, I planted some in regular potting soil and added an acidic fertilizer to the top, per the advice of my local nursery, and planted others, after reading about proper blueberry soil, in a mix of pine bark, peat moss, and soil, and added that same acidic fertilizer mixed right into the soil before transplanting.

The plants looked a bit distressed early in the summer, but bounced back and looked healthy by the fall.

I gave that acidic fertilizer away, and now need to figure out a plan for maintaining proper soil and PH this year.

I use only rain water on the blueberries. I have some organic fertilizers that I would like to use, including worm tea, soluble ericoid mycorhizae, kelp and blackstrap mollasses, but I think I will still need to lower the PH.

I've read so many alternative methods of lowing PH my head is spinning. And I have to be even more cautious/conservative, because they are all potted and a little too much of something could have a hugely negative impact. Any advice to gently/safely lower the PH in containers for a home urban orchardist would be greatly appreciated!

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You can add vinegar, which would temporarily lower Ph. For a more permanent effect, you can use diluted sulfuric acid which would react and neutralize calcium carbonate. The acid is sold as a "battery fluid, acid" in auto parts store such as Autozone ($4). You can use the sprayer nozzle like Gilmour 362 to mix in the acid while watering with the hose and cover large areas quickly.

Here is a link that might be useful: Gilmour 362

    Bookmark   April 8, 2014 at 11:47AM
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bamboo_rabbit(9A Inverness FL)


Fertilizer at planting time is never a good idea and might be why they were stressed.

Regular potting soil? That sounds like a recipe for rotted roots. They are still dormant? If so I would remove as much of that soil as you can and repot them using peat and pine fines.....I don't think trying to make regular potting soil more acidic is the best way to go.

Far as the others planted in peat and long as you use just rain water your PH should be fine. If you do need it a smidge lower and want to stay organic I would just use regular sulfur but you should not need it. Btw you can take peat moss and soak it in your rain water and it will lower the PH of that rain water.......

This post was edited by bamboo_rabbit on Tue, Apr 8, 14 at 12:28

    Bookmark   April 8, 2014 at 12:14PM
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but I think I will still need to lower the PH.My first thought in reading your post is that it is tough to control what you can't measure. Ideally you should have something way to determine the pH of your soil even if it is a simple soil sample testing kit like lusterleaf rapitest. Then you can determine whether any adjustment is even necessary before you start taking steps to do so.

Did you decide you don't want to use acidifying fertilizer? Is that why you gave it away instead of continuing to use that? If any adjustments are necessary, it would seem that would be appropriate to use especially since you are using rainwater to irrigate. An option for acidifying the soil would be elemental sulfur. I don't know if that would be against any organic route you are trying to take or not, but its hard to argue with elemental sulfur since it occurs naturally in soil. Perhaps there are organic sources of sulfur that were not sourced from the byproducts of natural gas or petroleum if that is what you are trying to accomplish.

This post was edited by charina on Tue, Apr 8, 14 at 12:37

    Bookmark   April 8, 2014 at 12:32PM
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So, so far the suggestions are:

(1) Apply diluted sulfuric acid

(2) Repot normal potting soil to more suitable soil and continue with rain water

(3) Treat water with Vinegar

(4) Treat water with Peat Moss

(5) Apply regular sulfur

(6) Apply elemental sulfur

B/R, if I knew then what I do now, I wouldn't have used that potting soil at all. I wasn't planning on repotting them this season, figured I'd wait til next spring, but do you think it would benefit them a lot if I did it now? I wasn't sure if the benefit they'd get from being in a better soil a year earlier would be greater than the added stress of getting transplanted 2 years in a row. What do you think? (...I wouldn't mind being able to apply the ericoid mycorrhizae directly to the roots, too., but seems like a lot of work if not really needed)

Starfinder, at what rate should I apply the diluted sulfuric acid without burning or killing the plants? My pots are all approx. 21 inches in diameter.

Charina, I haven't been able to get a good PH reading yet. I bought one of those PH readers with the two metal prongs, but it either doesn't work, or I can't figure out how to use it properly because I get the same exact reading everywhere I test it. I just picked up some more test kits yesterday and plan to test the soil tonight, but I think it's a pretty strong presumption that the PH has started, or will start to creep back up, if not controlled by me.

I actually traded the acidic fertilizer to some guy for gooseberry and currant bushes, as I was done with it for the season and wanted to revise my method this year. I prefer organic, but I'm open to all suggestions. At what rate would you apply the elemental sulfur to the 21 inch pots without burning or killing the plants?

    Bookmark   April 8, 2014 at 1:10PM
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shazaam(NC 7B)

BR is right -- if they're still dormant, repot them in an appropriate mix and be done with it. If done carefully, it shouldn't set them back much in the short term (if at all), and, by season's end, they'll likely be much more vigorous and healthy.

    Bookmark   April 8, 2014 at 1:47PM
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I wouldn't even begin to guess at a rate without knowing the current pH, and the pH of the water you are applying (which, if pure rainwater, is likely below 7.0). That is the thing - the rate of application of any material is a SWAG (sorry wild A guess) without information on what is being treated.

From what I read, both the bb roots and the fungi that form mycorrhizae with them prefer well oxygenated soil. It is postulated that is part of why bb roots tend to be shallow. Will they survive if not repotted? Probably. Could you provide better conditions for the roots and fungi by repotting? Likely. Gurus on the container forum advocate repotting periodically even when using well aerated slow decomposing mixes. It's just part of the cycle of pots (unless you are fruitnut ;-) leaving a bb in a pot for 7+ years).

    Bookmark   April 8, 2014 at 1:55PM
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fruitnut Z7 4500ft SW TX


You should see my 10 year old Star repotted once at 7 years. It's growing like a weed. Even my pH snafus haven't phased it. Guess I repotted with proper soil.

    Bookmark   April 8, 2014 at 3:10PM
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bamboo_rabbit(9A Inverness FL)

Definitely 100% repot them. Just rinse the old soil off and frankly if they are dormant I doubt it will set them back at all. I prefer bareroot plants to avoid the circling roots, just do it soon before they lose dormancy.

If you buy low PH test paper it would be easy to work out how much acid you don't have to know the soil PH to use the acid as long as you don't add any other acidifying materials that could cause the soil PH to fall. Adjust water to PH 5 and you are good to go and don't try to go lower than that . But and this is important....I don't think you have to......while rainwater may be PH 7 or close to it it is soft has no bicarbonates so any acid in the soil will drop the rain water PH instantly. People generally use acid to counteract the bicarbonates in the irrigation water as there is just too much for the peat and pine to handle. Because you are using the peat and pine and rainwater make your life easy.find a acid fertilizer you like and the plants will thrive. Trust me if I could use rain water I would..I would just have to build a 14,000 gallon cistern:)

    Bookmark   April 8, 2014 at 3:15PM
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