Blueberry plant went through a shock. Why?

Ash7681June 26, 2013

Hi, I potted a blueberry plant about two months ago that I had bought from a nursery. I used potting soil only in a 7 gallon pot. The plant was doing well and sending out new shoots and even the blueberries were ripening. Then, suddenly one day, most of the top shoots, including new growth, began to wilt. The only thing I can correlate was that I had gotten slack with watering for a couple days prior to this.

This made me realize that I had to hasten the task of acidifying the soil. I added a sulphur based acidifier and checked that the pH had dropped to the 6-7 range in a couple days. Then, the plant went into a shock. The leaves in the top shoots began to burn inwards, as depicted in the picture.

The plant is now recovering, and is once again sending out new growth. But I'd like to understand what made the leaves and top shoots burn inwards. Any comments or advise would be most helpful.

Thanks.

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edweather(Zone 5a/b Central NY)

You are fortunate the plant survived, and from what I can see it looks pretty good. You probably shouldn't have used potting 'soil,' but you seem to be getting away with it so far. And yes, you have learned that blueberries MUST be kept watered. They thrive in a pH from 4-5, but can survive in the 6-7 you have and the acidifier should help. I'm not sure what caused the leaves to burn. If you get a chance you might want to check out the Fruits and Orchards forum. There are some serious blueberry growers over there, and you might want to consider repotting it while it's still young into a better soilless mix.

    Bookmark   June 26, 2013 at 8:30AM
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fireduck(10a)

A...it is a bit of a guess when you do not have all the facts, but....we sometimes see the results of shock/stress and say "what did I just do?". However, often times it takes a week or two to see results ...good or bad. I am going with the lack of water theory. As stated above, there are better options for container mixes...but yours will work. See posts on here...

    Bookmark   June 26, 2013 at 10:54AM
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gardengal48

I'm not at all sure what the issue was with any 'potting soil' without getting any more specific than that. Commercial potting mixes are always referred to as potting soil regardless if there is any real "soil" in the mix - typically there isn't. Just assuming the soil is at issue here at all is entirely presumptuous.

I'd be more curious about the use of the sulfur acidifier and how it was used. Typically these are intended for inground applications only and I'd wonder about their applicability for containers. At first glance I'd guess this was a case of sulfur toxicity as browning/scorching and drying of the leaf edges is characteristic of this problem. And it occurred so soon after the sulfur was applied.

Perhaps the easiest way to maintain acidity in already planted containers is watering with an acidic solution, usually diluted vinegar or citric acid. I cup of household vinegar per one gallon of tap water is typically the recommended dosage.

    Bookmark   June 26, 2013 at 7:05PM
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shazaam(NC 7B)

I cup of household vinegar per one gallon of tap water is typically the recommended dosage.

Did you mean one tablespoon of vinegar per gallon? One cup per gallon is a LOT of vinegar and could very well drop the pH of the irrigation solution too low. To get the dose right, the OP should test the pH his or her water and then add enough vinegar to get the pH down to between 5 and 6.

As for the acidifier, what specifically did you use? If you used elemental sulfur, it will take a long time to work -- up to a year or more, especially since you're growing in a container. It definitely shouldn't have caused any leaf scorching at this point.

    Bookmark   June 26, 2013 at 8:49PM
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fireduck(10a)

I use ag sulphur in containers. The key is using small amounts. It is longer lasting (by far) than vinegar water.

    Bookmark   June 26, 2013 at 9:06PM
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shazaam(NC 7B)

The point of vinegar isn't too permanently lower pH -- it won't. Rather, it serves to temporarily neutralize bicarbonates and drop the pH of your water/fertilizer solution so that the plant can utilize the nutrients. Ideally, you start out with a potting mix that's in the right pH range (4-5 or so) and then add vinegar (or another acid) to your irrigation water if necessary (i.e. if you're using hard well water). If your potting mix pH is too high, then you have the choice of repotting in a more appropriate mix or adding elemental sulfur to your existing mix. While the effect of the sulfur is permanent, it takes time (potentially a long time) to act. While you wait, acidifying your irrigation water should help to make nutrients more accessible to the plant.

    Bookmark   June 26, 2013 at 9:54PM
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edweather(Zone 5a/b Central NY)

gardengal48,

"Commercial potting mixes are always referred to as potting soil.."

I beg to differ, but no they are not, and one should check the label to make sure that they are not putting dirt into their container if they don't want any dirt. You said it yourself, by calling them commercial potting mixes. There are plenty of mixes that are called exactly that, "MIX," and not soil.

If one wants to grow in containers it behooves one to do a little research into what will be the best growing medium. It all starts there.

    Bookmark   June 26, 2013 at 10:04PM
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gardengal48

edweather, you are splitting hairs.

The term "potting soil" is so well used and recognized as a soil-less container medium as to be practically synonymous for all intents and purposes.

In any regard, the soil is not the issue - it is the attempt at acidification. The plant shows clear evidence of sulfur toxicity or other fertilizer burn. That's why I questioned what method of acidification was attempted. Agricultural sulfur is unlikely to be very effective in a container situation. First, it has to be oxidized by soil bacteria to be converted into an acid and lower pH. Since there are minimal populations of soil organisms of any kind in a soil-less potting medium, this is not easily achieved in the first place nor is it likely to happen quickly.

And yes, the ratio is 1 CUP of vinegar to one gallon of water - that is a 15 times dilution of a relatively weak 5% acid. Not enough of a jolt in pH to cause concern but enough to be of benefit to the plant. 1 tablespoon is not enough to have any measurable effect on pH.

    Bookmark   June 28, 2013 at 6:24PM
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shazaam(NC 7B)

Agricultural sulfur is unlikely to be very effective in a container situation.

It can actually be much too effective. A frequent contributor in the fruit forum ended up with pH readings below three in containers that were amended with too much elemental sulfur. Yes, given the biological action that's required, it's not as effective in containers as in the soil, but that doesn't mean that it's ineffective. It just takes time.

And yes, the ratio is 1 CUP of vinegar to one gallon of water - that is a 15 times dilution of a relatively weak 5% acid. Not enough of a jolt in pH to cause concern but enough to be of benefit to the plant. 1 tablespoon is not enough to have any measurable effect on pH.

I don't want to be argumentative, but can you provide a reference for that claim? One tablespoon does have a measurable effect on my well water, and I don't recall ever seeing anyone recommend one cup per gallon (even for blueberries). Regardless, there's a simple way for the OP and anyone else to determine exactly how much vinegar to use -- test the pH of your irrigation water with an inexpensive test kit or strips.

This post was edited by shazaam on Fri, Jun 28, 13 at 19:48

    Bookmark   June 28, 2013 at 7:09PM
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Ash7681

Folks, thanks for the responses. Regarding the question about the acidifier formulation, it is made from elemental sulphur and gypsum.

    Bookmark   June 28, 2013 at 11:34PM
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edweather(Zone 5a/b Central NY)

gardengal48, Not splitting hairs. If someone wants fine mineral soil particles that will easily compact, in their containers, more power to them. The point I am making is that starting with the correct container medium, especially for blueberries, will eliminate the problem being experienced now by the OP. Most blueberry growers who grow in containers use some combination of pine bark, peat and perlite. Buying a blueberry bush and then potting it in any xyz potting soil is not the way to go. I don't know any blueberry grower that would suggest that. My blueberries are growing in a mix of pine bark mulch, peat and perlite. No worries about pH here. When watering, 2 Tablespoons of vinegar per gallon brings the water down to a pH of about 5.

    Bookmark   June 29, 2013 at 12:21AM
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shazaam(NC 7B)

Regarding the question about the acidifier formulation, it is made from elemental sulphur and gypsum.

How much did you add? While I don't know enough about elemental sulfur to say this with certainty, my understanding is that it shouldn't have burned your plant at this stage. As mentioned above, microorganisms have to convert it to sulfuric acid before it can have an effect on pH, and that takes time.

As for what did cause the leaf damage, that's tricky to say. I let two potted blueberries get too dry a couple of years ago, and the end result was significant foliage and stem die back. That might be what happened to your blueberry. Then again, they're also sensitive to waterlogged soils, to overfertilization, to high soil temperatures, and so on. Nonetheless, they're also very resilient. In my experience, the key to keeping them happy is to provide an appropriate potting mix (peat and pine bark are ideal components), to keep the mix damp but not excessively wet, to irrigate with rainwater (ideal) or acidified tap water, and to fertilize modestly but consistently.

    Bookmark   June 29, 2013 at 11:12AM
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