In the big batch, you use 2 to 3 cubic feet of pine bark fines. When I make 5-1-1, I use 5-gallon and 1-gallon paint buckets to measure my materials, and I try to use 5 parts PBF to 1 part of each of the other two components. The paint buckets are measured in liquid gallons, and I use liquid gallon measurement for all my components, so I don't worry about the difference between liquid and dry gallons (one cubic foot is 7.5 liquid gallons or about six dry gallons in the U.S.). Since your barrels are probably measured in liquid gallons, you don't need to worry about the dry measurement either.

This is gardening, not baking or rocket science. You will need roughly 105 to 110 gallons of final mix for your four containers. That would be approximately five 2-cubic foot bags of bark plus 2 cubic feet of peat and 2 cubic feet of perlite, plus about 6.5 cups of lime, and if you choose to use it, about 6.5 cups of controlled release fertilizer.

Personally, I mix it all to my own specifications... depending on what I'm growing, where, and when, and how....

A bit of change can be good...

Thank you both! So it's more proportion that actual measurement, I should have seen that. I do understand that PBF are the ideal, but DH is a bit heavy-handed when it comes to watering, so I don't think I want to go too fine, thus the small bark mulch, There's no sapwood that I can tell through small holes in a couple of bags (not by me, I swear!), but mostly chunks (chips?) under about 1/2" with some shredded mixed in.

I add crushed egg shells to vermicompost for houseplants, and am wondering if I'm correct in thinking that when using this mix, the lime is more available to the plants?

Lynn T

Definitely use the dolomitic lime. It takes forever for eggshells to break down and the calcium they might provide is not taken up by the plants. Also, it is difficult to overwater 5-1-1 in a container with adequate drainage holes, especially outdoors in the summer. Don't leave out the finer stuff.

Thanks again - all advice noted and (I hope) balanced for DH to water enough to grow his veggies. He's actually excited about this new project!

I cannot say it enough times - thank you!
Lynn T

I wish my DH was enthusiastic about watering! I have so many containers going in the summer since I joined this forum that it takes me about 10 hours a week to water adequately at the height of the season. I would encourage the enthusiasm!

Oh, I don't discourage him. I just make sure I use slow release fertilizer liberally. It doesn't release so slow when it gets running water every other day...

Mixing 5-1-1 is just in relative proportions. You can use anything of any size; bucket, pot, bin. just measure 5 time bark, one time perlite, one time peat moss. If you are making a big batch just multiply the numbers. I dump all my measured stuff on a tarp and mix them all together and store it in a barrel

But if your question is how much you will need to fill two 30 gallon container (60 gallons) , just take roughly 6 gallons per cubic foot. So roughly you will need 10 cubic feet of bark, 2 cf of perlite and 2 cf of peat moss: You will end up with some extra for other potting needs. If you want the total to be just about 10 cf, then take 7 cf (40 gal) of bark, 1.4 cf(8gal.) of perlite and 1.4 cf (8gal) of peat moss.

Thing to remember is that 5-1-1 is just a ball park proportion. I may add more or less peat moss depending on how fine or coarse the bark material is. With coarse bark you may also use less perlite because it will have less water retention capacity. In other words : Too coarse bark, too much perlite will end up with a mix with very low water retention.
Not exactly a perfect science in a chemistry lab.