How to know how much soil to buy

I need to make a raised bed for my new Irises. But I'm on a tight budget. So if I build a raised bed 1' x 12' x 8" deep, how much soil would I need to buy. Also, can I stretch the soil a little further by mixing in some perlite or something else like that? I need to get my irises planted and I was going to buy two 12" 2 x 4s and then one for the ends. Will that be deep enough for them? Any suggestions that you have would be greatly appreciated.

Thanks,
Jesse

Irises love good drainage, so perlite probably would be good. Some people down the road from us have some TBs planted in what appears to be pure sand (we're in the desert).

What type of dirt will you be putting your raised bed on? Till it up and it will add fluff and let the roots go down deeper, thus taking advantage of the raised soil and the dirt below.

1 bag of dirt is about 2 ft wide and 3 ft long and 6" or so talk. Very iffy guestimate might be that you can get away with 4 bags? Especially if you mound it towards the center of your bed and plant on the mound?

Good luck - some are going to be spending a few years in my veggie bed for lack of another raised bed. Now I just need to find a home for the garlic bulbs when they get here...

If you get topsoil by the truckload, it generally comes by the cubic yard. 1 cubic yard equals 27 cubic feet. Around our area, topsoil by the yard (delivered price) is far cheaper than bagged soil. The bags of topsoil sold around here I think hold either 2 or 4 cubic feet.

A cubic foot is 12 by 12 by 12 inches. So a cubic foot of soil will cover two square feet, 6 inches deep.

To figure out coverage at different depths, multiply the number of cubic feet by 12, and then divide by the number of inches of desired depth. For example, 1 cubic yard (27 cubic feet) will cover 54 square feet (6 ft x 9 ft), 6 inches deep, or about 40 square feet, 8 inches deep.

For your proposed bed (12 square ft.), 8 cubic feet of topsoil would give you 8 inches of depth. That's 4 bags, probably.

Depending on the looks of the topsoil, you might also choose to mix in a little compost or other organic material, or use perlite to make up some of the volume as you suggested.

Jesse, I'm so glad you asked this question because I wanted to know the same thing. Good advise given as well!

Deborah
Deb

See, and you thought you would never again use the algebra you learned in high school.... LOL, it comes in handy for these sorts of conversions!

For me, it also helps to visualize a cubic foot as a literal cube of soil, 12 inches deep... that way, you can skip the algebra to figure out that 1 cubic foot would cover 2 square feet 6 inches deep, etc.

And if you forget the number 27 for the cubic feet to cubic yards conversion, just remember that a cubic yard measures 3 ft x 3 ft x 3 ft...

Jesse, I dig and renovate a large number of beds every year. The guy who sells me the truckloads of soil is an excellent resource. Rather than trying to figure it out myself, I've enlisted him as an ally, explaining what the irises need, and having him suggest amounts. Obviously this hinges on you finding an honest supplier but I think most people are - they know you won't return if they steer you wrong, after all.

In my case, Stan now phones me when he has a chance of picking up something special that I might be able to use - most recently, he called to ask if irises liked mushroom soil, because a delivery had taken him to Chester County (in PA) and he figured he might as well drive back with a full truck if I wanted some.

Because he knows I trust him and because he knows I'll give him my business, he takes good care of me even though I'm sure I'm not a major customer. See if you can find a small business in your area and cultivate a relationship with them - maybe you can find your own Stan!

katie

I'm looking, I'm looking - Stan, do you make it as far west as Nevada? So far, two different companies has tried to pass off sand (more that 50 %) mixed with dried weeds and a little clay as top soil. Not quite what I'm looking for :-)

Would Stan deliver to Colorado? LOL.

Hey, greenjay, maybe if you and I went in together on an order it would be worth it for him to come all the way out this way!

I'm game!

Can't you just see Stan on an extended road trip / vacation out west, driving the biggest double semi load of mushroom soil he can handle.... LOL!

There are "Stans" in most areas, just keep calling and asking around...