Last year I used a very crude method -- handfuls. I'd be interested in knowing how those with more experience do it.

As a bit of a side note here, many on this forum will likely suggest that the soil recipe you are using is not suitable for container gardening (unless the containers will be placed in the ground or unless you will be using wicks to drain excess water out of the container).

I have not had any experience with using the aerated mixes advocated here, but the theoretical benefits of air in the rootzone make perfect sense to me, and I will be using a highly aerated mix this year.

Last year I used the same ingredients you listed and while my crop wasn't a total failure, it was a failure. I got about 20 tomatoes out of 30 indeterminate plants, and most of them were tiny or had blossom end rot due to alternating drought/flood conditions created by the "soil" I used and my own ignorance. I can't recommend use of a highly aerated "soil" because I have yet to try any, but there are plenty of folks on this forum who have used them to great result.

Without commenting on the reason for the mix, here is what I would do. Your perlite and vermiculite should always be moistened before using or even handling as breathing dust of either is not recommended. I keep each of them in 30 gallon plastic garbage cans with tight lids. As I fill them a add water to evenly moisten the whole can. If I want a mix of 30% three ingredients I use a scoop to add one scoop of each, repeating as many times as needed for the volume desired. Al

If you make the soil you described, I fear you will have trouble with collapse and water retention. You have i ingredient that is very prone to breakdown and lots of water retention - the vermiculite. The compost, if it is finished, will be very fine in texture. If it is not finished and is in larger 'chunks' it can break down quickly and N immobilization could be an issue. IF you have a soil that is composed of 2/3 fine, water-retentive ingredients, you cannot expect a 1/3 perlite component to give it the aeration/drainage needed. To envision this, ask yourself how much perlite you have to add to pudding to make it well-aerated and free draining.

If you decide to go forward with your plan: soils needn't be so precise. Measure the compost by volume when it's damp, but not wet (can't squeeze water out when you compress it in your hand). The perlite & vermiculite will be dry - just use the same container you used to measure the compost.

I think you would probably do much better with a soil something like
5 parts pine bark fines
1 part peat (or use your compost)
1-2 parts perlite

Al

The percentages I listed, although I did not specify, were not the actual mix percentages, but rather for illustration and ease of computation. I was really trying to determine the method to use for comparative measurement.

The compost I have is actually called potting soil and consists of mostly "partially composted pine fines" with a small percentage of pine fines and about 15 to 20 percent compost and sand.

I plan on using this in SWC's and I will need to add some perlite and vermiculite to the above to provide aeration and reduce weight (water retention).

I also want to use some MG Potting Mix in my SWC's to compare. There again I have a 2 cu. ft. bag and a 30 gal. container, but I may use the Mix in my double 5 gal pail SWC's.

Thank you all for your input and I think I have a handle on how to mix these together now. I will post later as to the comparative success of my formulae.

I plan on using this in SWC's and I will need to add some perlite and vermiculite to the above to provide aeration and reduce weight (water retention).

Perlite will reduce water retention and weight, but vermiculite will increase both.

Vermiculite is a water sponge and will hold more water than anything else in the mix. It is a common misconception that vermiculite and perlite are interchangeable. They are actually like night and day.

AS others have said above, I won't comment on the relative fractions.

But mixing for containers - any containers - is easy.

What I do is clean the wheelbarrow and use a 5-gal bucket for my fractions, mix in the wheelbarrow and transfer to containers. You'll be surprised how easy this is. Remember to clean your wheelbarrow, I hose down and wipe with weak bleach solution, then hose clean again; your shovel should be cleaned this way as well. Never had a problem.

Dan

Dan's offering reminded me of another way for mixing really big batches: Simply combine all the ingredients on a large tarp on the lawn and moisten slightly. By pulling on alternate corners and rolling/folding the ingredients over - the big batches are quickly & thoroughly mixed. Then, if you fold the tarp over the newly made soil and allow it to set overnight before filling containers, the moisture will diffuse through the soil and 'break' the hydrophobic (water repellent) tendency of very dry bark/peat.

It is best to mix your soils a couple of weeks in advance to allow for the reactive phase of the lime. I didn't understand why only my early tomatoes often showed some BER until I learned that it was because I was using fresh soil and the lime was unavailable.

Al