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I live in a region of the upper midwest where we have high-pH soil; my soil's pH varies between 6.8 and 7.5. Accordingly, our extension office recommends planting blueberries in buried containers with 0% native soil in the mix. But researching pots large enough for a mature blueberry bush, (around 35 gallons?) it would cost me $500 to buy 22 such pots at the cheapest source I've yet to find. Surely there's a cheaper way to shield their rootzones from my soil's pH?

  • What about planting in a peat moss/bark mix in a buried grow bag? Would the permeable fabric of the grow bag add any protection against the higher pH leaching into it?
  • If not, what about just filling the hole with the peat moss/bark mixture without any container/bag at all? How long would that retain a friendly pH?
  • What about heavy-duty plastic bags or just plastic sheeting with a few holes punched in the bottom lining the hole?

I do not plan on digging this out each year. They are intended to be permanently in-ground. They will not be in a row but scattered with lawn between them, so a trenching solution wouldn't work. Any advice?

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  • What is your soil's pH?
    – Jurp
    Feb 5, 2023 at 0:15
  • it varies between 6.8 and 7.5
    – Paul W
    Feb 5, 2023 at 1:32
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    The real question is whether you see blueberries growing in your area. If not then a raised bed might be the only solution
    – kevinskio
    Feb 5, 2023 at 14:11
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    I tried growing blue berries in northern IL; not worth the effort. I found a pick yourself blue berry farm in sandy acid soil near the Kankakee River. Big strong heavy bearing bushes. Feb 5, 2023 at 16:16

2 Answers 2

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The fact that all of the possibilities that you've mentioned in your question will break down over time means that, long-term, they're probably not great solutions (the only exception is the 35 gallon pots and maybe the permeable bag). The peat moss might give you a couple of years and acidify as it's breaking down, but when it's gone the soil in your pots (and the plants) will have sunk probably half the original volume of the peat. Same with the bark. Even black plastic will break down in soil.

I used to live in a higher-pH area in Wisconsin and tried growing blueberries in native soil but on the edge of a pine woods. They were unhappy but didn't die. Had I known about soil sulfur, I would've used it.

Basically, to plant in native soil (or in soil that you've brought in to the site and, I assume had pH tested before purchasing) you need to artificially change the soil's pH every year.

You use two natural chemicals to alter the pH: either aluminum sulfate/ammonium sulfate and sulfur. The sulfates are used as a drench around the plants and leach out of the soil fairly quickly, so you'll have to re-apply several times or more a year (per the instructions on the bag); the sulfur decomposes slowly and leaches slowly. It's applied to the top of the soil as granules or powder, twice a year (I do it in the spring and fall; roughly on Easter and Labor Day). If you apply the sulfur and then use one of the sulfates for a year, the pH will be lowered by the sulfate while the sulfur is decomposing and changing the pH on its own. After a year (or until your bag of sulfate is gone, whichever is LATER) you no longer need to apply the sulfate any more. The good news is that both of these chemicals (well, one chemical and one element) are inexpensive and will not harm you, your children, your pets, or the environment.

This is the schedule that I recommend to my customers purchasing blueberries:

  1. Get a large bag of aluminum sulfate or ammonium sulfate and a larger bag of elemental (soil) sulfur.
  2. Mix the aluminum or ammonium sulfate with water per the instructions on the bag and drench each plant.
  3. At the same time, scatter the soil sulfur around the soil of each plant, in the amount recommended on the instructions.
  4. After at least a year, you can discontinue applying sulfate.
  5. Spread the sulfur in spring and fall, every year.

Also, use a woodchip mulch to help feed the shrubs and to keep the soil moist. You don't need to work the sulfur into the mulch unless you feel like it.

UPDATE

This page from the University of Wisconsin Extension Horticulture department recommends using sulfer or aluminum sulfate to lower pH in soils with pH as high as 7.5, although I think at that level it'll only lower it to 6.5. It should apply to those areas of your property where pH is currently at 6.8.

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  • Excellent info, thank you.
    – Paul W
    Feb 5, 2023 at 20:49
  • Any thoughts on how any of the following would stand up in the soil over years, and effectiveness in blocking pH? (1) 15 mil LD polyolefin concrete vapor barrier, (2) 15 mil PE pond liner, (3) 8 mil reflective aluminum/mylar+PE scrim radiant vapor barrier, 0.0 perms.
    – Paul W
    Feb 6, 2023 at 2:13
  • My major concern with the vapor barriers and pond liners is drainage. Without adequate drainage in the planting hole (and AFAIK all of the solutions in your comment are impermeable), rain and water from external watering can easily build up in the planting hole and potentially drown the plant. You'll need to put a large number of large holes in the barriers to facilitate water passing through to the soiil below. Similarly, "foreign" soil in the planting hole can cause a perched water table with similar results, esp. if native soil is clay. That's why I recommended planting in native soil.
    – Jurp
    Feb 6, 2023 at 13:23
  • I was planning on punching drainage holes in whatever I use. My native soil is sandy. I like the idea of using some of my native soil, but all my sources (UW Madison Hort. Extension, WPR, state newspapers, local farmers, etc..) are all saying either trench or containerize with 0% native soil, our pH is too high to chemically lower.
    – Paul W
    Feb 6, 2023 at 15:55
  • Interesting that UW (Wisconsin, not Washington, I assume) recommends this (and I see the pubs on their site) because an Extension agent is the one who told me about acidying the native soil. Times change... UKentucky goes farther - they say if soil pH too high, then just don't plant the blueberries. If you're into experimenting, use non-native soil in an unlined hole (mix the bottom 2" of the soil with the top 2" of the sand to help with drainage), then acidify it as noted in the answer. As long as the non-native soil is at 5.5 or less, the sulfur will keep it acidic over time.
    – Jurp
    Feb 6, 2023 at 22:16
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Something like pond liner will isolate a trench or individual pit (at the cost of needing more for equivalent area in pits than as a trench) (you need drainage holes in it, hopefully obviously.) I have older books that suggest using tar on the inside of concrete planters to prevent contact with the acid soil, but those probably predate the somewhat less generally toxic pond liner being available. Unlike "plastic bags" pond liner has a long useful life, while it is impermeable, unlike a typical grow bag.

Regular applications of sulfur are a fairly common, if slow, method of keeping a blueberry bed acidified (without needing isolation.) But if your soil is particularly alkaline isolation might be worthwhile as well. Because blueberries are generally shallow-rooted, you don't need a deep trench or pit.

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  • Pond liners, what a great idea! I'll have to check those out.
    – Paul W
    Feb 5, 2023 at 20:49

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