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Al - I need help with soil mixtures for blueberries.

Posted by LIG-LifeIsGood 8 (My Page) on
Fri, Oct 19, 12 at 13:24

Long time lurker - first time posting.

First of all - a big thanks to Al and everyone else who work so hard to answer all the questions that we(the less informed, but eager to learn plant lovers) come up with. I have been reading the posts daily for about a month now and although I am much better informed as to what I have been doing wrong,I am also not sure about how to proceed with the soil mixtures for my blueberries. They will be planted in three different locations and conditions.

(1) Containers in a greenhouse.

(2) Raised cedar beds - 3'X3'X20" high. Placed over 1/2" hardware cloth over disturbed clay soil.

(3) In ground - clay soil. Holes are 3' across and approx 14" deep. The blueberries will be planted in 1/2" hardware cloth baskets(also 3' across) that will extend about 6" above the natural soil level in order to help with drainage.

I live in the Vancouver, WA area(zone 8) and have clay soil. I think the native soil here is somewhat acidic as the natural flora is mainly fir trees but I have never had it tested. The reason that I am using hardware cloth baskets is the horrific mole and vole problem. The average rainfall here is about 35"/year with the summer months being completely dry and the rest of the year being rainy. I also water with well water that tests out at about 8 - so I am aware that I need to add vinegar to bring the PH down when watering the blueberries. All the blueberries will receive full sun. I have unlimited amounts of fir bark(both composted and uncomposted) in varying sizes available locally. I also have perlite, peat, granite and Turface available.

I have read a lot about the 5-1-1 mix and the gritty mix and would like to try them both for the container plants in the greenhouse. Would one be better than the other and do I need to make any adjustments to Al's original formulas to accommodate blueberries specific needs?

As far as the soil mixtures for the raised bed and in the ground baskets should I use variations of the 5-1-1- mix and should I add in any of the natural clay soil?

I am aware that the in the ground holes are the equivalent of bathtubs and since they are actually dug right now and we had approx 2.5 inches of rain in the last week I am able to observe firsthand what happens when it rains on clay soil. Several of them do accumulate about 1 inch of water in the bottom of the hole and it takes approx 24 hours for it to drain completely. Unfortunately I have no choice but to use them at this time and maybe in the future I can replace them with raised beds.
History-I have been trying to grow blueberries for about 10 years now with very limited success. The things I know I have done incorrectly so far: (1) Covering the surrounding area with weed fabric and wood chips - it allows the moles and voles to run rampant under the fabric, destroying the roots of the blueberries while shielding the rodents from predators. (2) Amending the holes with commercial compost and a 5-way potting mix from a local nursery. I think that these amendments were ph adjusted with lime (3) Watering often in the summer with straight well water at ph 8.
Sorry this is so wordy - I tried to cover everything I could think of.

Follow-Up Postings:

RE: Al - I need help with soil mixtures for blueberries.

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Sun, Oct 21, 12 at 11:22

Hi, C - It's really great that you made your presence known - welcome! ;-)

I think, for the raised beds and in-ground plantings, you can use something much heavier than you could in containers, simply because it's what's underneath the raised beds that will ultimately determine how good the drainage is and will be what you primarily need to be concerned with. I'm thinking 60-75% decent topsoil or coarse sand mixed with reed/sedge peat, sphagnum peat, compost, even chopped up leaves if you don't mind adding the extra N to compensate for N immobilization.

If you live on a slope, maybe you can shape the slope or dig a ditch/trench/other to divert surface water away from the planting spots. BBs love water, but hate wet feet. Here in MI, they grow them commercially in low areas with sandy soil and a high water table.

Either the 5:1:1 mix or the gritty mix will work well in containers for BBs. The only modification I might make is to use gypsum as a Ca source (if needed - your fertilizer lacks Ca ....) instead of dolomite. If your fertilizer lacks Ca, it usually lacks Mg, so you'd then need to include a little Epsom salts in your fertilizer solution.

Honestly - if I was using containers, I'd partially bury the containers and grow them in the same mix as I used for raised beds.

I would also consider as an important part of your success, getting that soil test and telling the nearest county extension service people what you're trying to achieve. They'll have recommendations about what to use for proper nutritional supplementation and bringing pH in line.

Best luck, C.


RE: Al - I need help with soil mixtures for blueberries.

Al-Thanks for the response.
I am a bit confused about your advice on the mix for the in-ground and raised bed planting. You advise a heavier mix for both as compared to a container mix because the drainage would be better when in contact with the native ground soil. Since my native soil is clay wouldn't the drainage be rather poor? Also you recommend 60-75% decent topsoil - I am not sure what that is. All we have here is clay soil unless you are referring to something I would need to buy from a nursery. If that is the case, would the PH of the topsoil be an issue? I am always a little gun shy about buying bulk mixes as I never know what the origin of the product is. Also - if the topsoil is making up 60-75% of the mix, what is making up the remainder?

I originally made a small amount of the following to fill the in-ground holes, but the resulting mix would not drain properly:
(1) part composted fir bark
(1) part peat
(1) part native (clay)
(1) part perlite

So I dug it back out and amended until I had this mix which drained much better:(I have not actually filled any of the holes at this time)
(3) parts composted fir bark
(3) parts peat
(1) part native (clay)
(2) parts perlite

After doing a lot of reading on the forums I was thinking that I needed to up the ratio of fir bark to peat to 2 parts fir bark/1 part peat in order to not only encourage drainage but also to create a more stable mix for longevity.

I am not arguing with your recommendations, just trying to understand why you are advising topsoil instead of your usual fir bark, peat, etc mixtures.

RE: Al - I need help with soil mixtures for blueberries.

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Mon, Oct 22, 12 at 17:32

No matter what you use for a soil in clay depressions, drainage is going to be controlled completely by the percolation rate through the clay; so no matter what you use, it's going to drain at the same rate as the clay. If you filled the clay hole with 3 lb boulders, it will drain almost at the same rate as if it was filled with clay. Clay has a slow perc rate, but tremendous capillary attraction, so as soon as a molecule of space is available in the surrounding clay, it will 'suck' a molecule out of whatever material is in the hole to fill that space.

Re the experiment you tried - both of the mixes should have drained at fairly close to the same rate if all else was equal other than the composition of the mixes. I would expect the largest variation in the drainage rates (from the clay depression) to depend on how much water was in the clay surrounding the hole at the time of the experiment - with the slower time occurring when the surrounding soil was closer to its saturation point.

The key to increasing your drainage rate in your in ground application is ensuring the water in the depressions has a place to drain TO, instead of depending on percolation. If you depend on percolation, it hardly matters what you use as a soil in the depression.

I suggested topsoil or sand to help you minimize shrinkage due to gassing off of the organic fraction. There is no advantage in having a soil with a 75% organic fraction as opposed to a 75% mineral fraction when it comes to raised beds. Any advantage of the higher organic fraction would come in the form of the larger % of OM providing more food for soil organisms, which will eventually improve the tilth of the soil surrounding your plantings, but that gain is offset by the fact that that just builds a bigger bathtub, which brings us full circle to having a place for the water to drain TO, so you can direct it away from your plantings, minimizing the bathtub effect.


RE: Al - I need help with soil mixtures for blueberries.

Although it seems counterintuitive that the drainage rates in the holes would be almost the same for 3 lb rocks as clay soil, I am finally beginning to get it. Since I get to observe the affects of relentless rain on seven 3' wide by 14" deep holes dug in clay soil I can say that even when the holes are empty there can still be drainage issues. There is a slight slope to the row of holes dug for the blueberries and the three holes at the low end of the slope accumulate about 1" of water that is very slow to drain while the holes at the higher end of the slope do not accumulate any water.

I have not previously thought about soil ingredients as being either mineral or organic and just assumed that topsoil was made up of decomposed plant material. But if I am interpreting you correctly it looks like topsoil must be more mineral in content and therefore more stable an ingredient over the long haul.

So if someone used a mix similar to your 5-1-1 mix in the ground or a raised bed - what would happen to the soil over time? Would it break down and compact? If it compacted what would one do to correct the problem?

Also - you mention course sand. How large are the particles in course sand and where would you advise I look for a supply of it?

Thanks again for your help.

RE: Al - I need help with soil mixtures for blueberries.

  • Posted by DWD2 10a, Sunset 17 (My Page) on
    Tue, Oct 23, 12 at 13:56

Connie - The advice I see from blueberry growers is to use a raised bed for clay soils. You do not need to build any sort of fancy structure. Lots & lots of commercial blueberry operations in Oregon & Washington have mounds of various growing mixtures on top of the native soil. Since blueberries have shallow root systems, you can easily build a big enough mound such that the roots are contained in the mound which is your raised bed. The growing mix allows you to control the pH and water dynamics which are very important. While there is slight variation from blueberry expert to expert, the consensus is pH 4.5 to 5.0 as the ideal range. There are plenty of pictures & descriptions in the book "Blueberries: For Growers, Gardeners and Promoters." I think it is the best $60 dollars you will spend to grow blueberries. Below are a whole series of links to different blueberry resources. While the 5-1-1 mix should work, you may decide on a different mix after a bit more reading.

Here is a list of links to a number of free publications that I have found very helpful. I have been growing blueberries in pots very successfully for several years thanks to what I have learned in these & other publications.;jsessionid=34C1D8724B28E1018BFDFB7C8DC84200?sequence=1

You are fortunate that there is an excellent blueberry group at Washington State University. I believe you should be able to contact a blueberry person for advice through information found on this link.
or your WSU Extension office.

For your mole and vole problems, you should find some very useful advice here:

Good luck with those blueberries!

Here is a link that might be useful: Blueberries: For Growers, Gardeners and Promoters

RE: Al - I need help with soil mixtures for blueberries.

WOW! Thank you for all the links to blueberry growing sites. I really appreciate all the effort you went to and I will investigate each of them and the book you referenced for more information.

I hope I didn't appear to be argumentative when I asked you about how the 5-1-1 mix would do over time in either a raised garden or in the ground. I actually was not asking in reference to planting blueberries but rather as a planting method in general as I am trying to wrap my head around many of the basic concepts of soil composition that you write about. I really had never thought about the makeup of soil or potting mixes, etc until I began to read your posts and then suddenly a lot of the problems I have had in the past began to make more sense to me. So again my question about what happens to a mainly organic soil mix in either a raised bed or in the ground is only to help me to understand how best to proceed with future mixtures.

RE: Al - I need help with soil mixtures for blueberries.

Al-scratch that last post of mine as I just realized that the blueberry links came from DWD2.

DWD2-Thank you so much for all the links to blueberry information sites. Again I will follow up on them ASAP and try to glean as much help from them as possible.

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