(3) 2x10" x8' MCQ or ACQ treated wood,
(12-15) 3" long screws(or 16p nails if you do not want to ever take it apart) -galvanized for ACQ wood,
3 bags of *composted* cow manure(e.g., Black Kow)
1 3.8 CuFt Sphagnum peat moss
3 40# bags of (organic) peat humus
4 qt of perlite
Take off about 2" of the gravel in a 50" x 100" area.
That's the location for the raised bed.
(the bed does not have to go on the run but it sounds pretty good to me)
Cut one of the pieces of lumber in half -that's your 4' ends.
Nail or screw the end pieces to the 8 foot boards. I rec' that you do that near, very near to where it will be placed. It can be moved but it ain't light.
You now have a raised bed frame.
Blueberries (regular) roots only go a foot deep. With "dwarf" you might get by with 2x8" lumber. I don't know. Up to you.
Optional but probably desirable is to line the bottom with landscape fabric to slow down some of the water loss to the *great* drainage underneath. Cardboard is just as good -better since it is free.(one does the same on top of normal ground to stop weed growth)
Second option is to line the bed frame with plastic. I swear that it is not necessary with MCQ or ACQ treated lumber but some people are uninformed &|R squeamish. The bags make a great liner if you can arrange to empty the bags so they can be cut and placed before the ingredients get mixed & moved.
Mix the ingredients a little bit at a time.
I do about 1/3 bag of each until the wheel barrow is full. A shovel turning the mix until it is uniform works great. A concrete mixer, if handy, would be even better and a LOT less sweat,
That's about 3 cu.ft and can be dumped into the raised bed. Repeat. Repeat.
A little more detail: I screen all of the mix thru 1/2" sceen to break-up chunks and get out rocks, big sticks, etc. Anyone that has a compost bin does the same thing with the compost so it can be used. If you don't screen be prepared to break chunks by hand or with mixing tool.
Also, it can get a little tricky getting the right amounts in there without overflowing the wheelbarrow. The idea is to get equal amounts by volume of (1)composted cow manure, (2)peat and (3)humus while adding ~ 1-1.5 qt of perlite and a *sprinkling* of epsom salts. Adding more or less of the perlite is a judgement call.
(NOTE: If it was not blueberries needing acidic mix, lime would be added too.)
There should be about two inches or so of space to the top of the frame. That's space for mulching during winter and heat of summer but it is not really required. You can fill the frame all the way to the top if you desire.
Transplant and water.
You should note that sulfur or aluminum sulfate amendment is missing. The reason is that those need to be added after so you can get the correct amount for the blueberries to have that 4.5-5.0 pH that they need. You can determine how much by testing the pH of the mix. It *should* be about 5.5 but I cannot say for certain(too many factors). While mixing the correct amount into the specific planting zone is best you will have to test the soil first then do the transplants later. That would be smart thing to do and actually a pretty good thing so the bed has time to 'rest' so all the microbes can get busy.
Also, I would rec' adding mycorrhizae amendment(E.g., Bio-Tone) *in the hole* just to make sure those fungi are present for the blueberry roots. Blueberries' roots require them to function properly.
Just about anything will grow great in the mix and NO weeding.
Irrigation is *required* as it is normally for blueberries anyway. I rec' soaker hose for the job.
Obviously, you can make the bed more square, more narrow, longer or shorter depending on your needs. It takes four(4) wheelbarrows full of mix to fill the 44"x96" interior of the frame. After rains, it only has about one inch from the top which, IMO, is too full. To each his own...
If you change the size, you will have to calculate how much mix to buy.
However, once a year add a bag of KOW or other compost or composted cow manure which is normal for plants too.
For Goodness sakes, do *NOT* use "green" manure. It will burn and kill the plants - any plants - until it 'composts' which can take 6 months to a year.
The blueberries can be fertilized normally but I seriously doubt that any will be needed for at least a year.
If you only acidify the soil around the blueberries, the rest of the bed becomes a great place for other plants,
There is one shortcut I know. That's to buy a mix that already has peat and perlite in it. I use some called "LC1" but ithink "ProMix" is the same thing. It is more expensive and a little harder to figure the quantities but is faster than mixing all of it.
I won't kid you: this is *work* and will take some time. However once it is done the amount of time saved later is truly enormous.
I only wish that I had done that for my blueberries instead of putting them in the dirt and trying to acidify it. I am trying to fix that now by moving mix into the *berry bed around the plants.
No matter what you decide to do, remember,
To answer the simple way:
‣ For established 2 to 5 gallon (blueberry) plants, choose a 16 to 20 inch container. --( https://www.davewilson.com/homegrown/promotion/bluecontainer.html )
That's about a 10-20 "industry gallon" container.
Width x Height
25 gallon = 24 x 18
15 gallon = 18.25 x 16
7 gallon = 14 x 12
5 gallon = 12 x 11