How much soil do I need?

I'd fill the barrels half way with empty plastic bottles, lay landscaping fabric over them, then fill 1/4 the way with potting soil, add plants, fill with the remaining potting soil. The empty plastic bottles will keep the barrels light weight and portable. (Make sure there's a drainage hole at the bottom.)

Sometimes the amount of soil makes a difference in how well your plant does in the barrel... some plants have deeper root systems than others. I think I used a 3 cu ft bag of soil for my whisky barrels (remember it will pack down in time with watering)

Another thing about whisky barrels.... they are made of wood... and wood shrinks or swells according to the amount of moisture in the soil inside...and the spaces between the 'staves' can open up enough that any water literally runs right out.... you may need to fill the barrel all the way up with soil to keep it from leaking out all the water your plant(s) need to do well.

i agree with Diana, you should fill your barrels 1/2 way with something lightweight. I would suggest cut up pool noodles or as she says pop bottles...something that willnstill allow drainage yet won't be too heavy to move around.

I fill my tall large pots with styrofoam big squares of it, so it forms a platform in the pot, I then take a black thick trash bag (the thickest you can find) and place it on top of the styrofoam, fill it with dirt and put my plants in. I used to fill the whole thing up with dirt and it was so heavy I couldn't even move it. Oh, once you put the dirt in, trim the bag about 1-2" above the top of the barrel, it will sink down some over time.

I read that to cut back on amount of soil needed in real large planters, you fill bottom or 1/4 full of empty water bottles...I just received a large planter I will try this with in spring...and i suppose what you r going t plant in it and their root system .

Depending on what I plan to plant, I either fill the barrel up (for large permanent plants that will be staying there for years) with soil, or I place old shallow plastic flower pots (the sturdy ones you get in the nursery) upside down on the bottom of the whiskey barrel. Either way, I use some landscape fabric to line the barrel just before I put soil in. About a 3 cubic foot bag will fill a barrel planter. Sometimes the manufacturer puts a sticker on the planter saying how much potting soil you will need.

If it's a permanent planter arrangment, and it's very heavy from all that soil and the plant, they do sell little dollies you can place the planter on to move it around. Pricey, but they're worth it if you like to change your planting displays.

Everyone is suggesting you fill the barrels with something. They obviously didn't read that you will be using 16" discs to take up space in the barrels. Make sure you drill some drainage holes in the discs. Based on calculating the cubic inches of a cylinder, then converting the cubic inches to cubic feet you would need approximately 1 1/4 cubic feet of soil.