Cubic Footage of an Odd-Shaped Box

Since I'm going to place the SFG boxes on a slight slope, I need to figure out how many cubic feet of MM these boxes will hold. Figuring out cubic footage of a standard box is easy but if my boxes will look something like this.....



The green is the grassy slope and the tan is the box. The width of the box is 4 feet and the length will be 10 feet.

Other than addition, subtraction, etc. I am horrible with math. Could someone figure out the cubic footage of two boxes like the picture?

I would make it simple and less expensive by placing the box in the desired location, staking the downward slope side to prevent the box slipping, then backfill and level with local soil to within 6-8" of the top of the box. I would then fill that top 6-8" with Mel's mix. You can use the Mel's Mix calculator to figure out what you need.

My husband did this for you.

Just considering the top portion of your box, 8" X 4' X 10', you'd need 26 2/3 cu ft.

The sloped part is exactly half of that (since your top is 8" and the other side is 16"), so 13 1/3 cu ft.

So you need 40 cu ft of fill. (Mathematician's disclaimer: This is assuming your picture, which shows your 8" line not quite matching up on the left side, isn't exactly correct.)

I remember seeing in many films and books how folks with hilly land terraced their growing areas so they were leveled.

Can you possibly wedge a piece of lumber along the lower end with maybe some more lumber or even stray rocks along the sides and just fill that section in with any soil available to get the section level? Then you can put your boxes on level land to start with and use lots less Mix which will be lots more economical. No sense wasting Mix for the extra deep side if its not necessary.

When I installed a patio planter bed, it was 3 ft deep. This was before I learned about SFG and Mel's Mix, but I didn't want to waste money on filling that much depth with "good soil." I used a 2 ft 'base layer' using some fill dirt from the excavation for my garage foundation - a heavy clay soil with chunks of debris from a very old brick/stone house. But I did mix a LOT of compost into that base layer for lightening and nutrients. Even without the benefit of MM, I've been able to grow things easily in the top 1ft for many years with little nutrient replenishment to the top layer. So while I wouldn't fill all your slope with MM because of the cost, consider adding compost to your local soil to give it a little extra boost. All of this is just one case of planting though, not scientifically proven.

Wow....you guys and girls are cool. Thanks for helping me figure this out. I guess that would be very wasteful if I would fill the entire box with MM. Even with MM at an 8 inch depth, the vermiculite will cost me about 165 bucks, not taking into consideration the couple of trips I'd have to make with my car. I found Uline, using the database here, and it's about 30 miles from my house.

Unfortunately I live where there's a Home Owner's Association and they might complain if the beds at the side of my house don't look neat. I want this to be as neat as possible to avoid any potential conflicts. I thought of building the boxes with a plywood bottom and raising the lower side so that they're level, but that would definitely raise some eyebrows around here. So I'm going to build the boxes built the way the drawing indicates.

I think maybe I'll fill in the box with topsoil so that I will have an 8 inch depth of MM across the top. I definitely have enough compost to fill the bottom of the boxes(and MM on top) but I think I would rather save the compost to augment the flower beds around the house.

Maybe if I would've paid attention in math class in high school, I would've been able to figure out the cubic footage on my own.

Thank you very much for your advice on this.

Why not just terrace the plot by digging out the slope portion of the area on which the box is planted?

Tom

tomperrin wrote:Why not just terrace the plot by digging out the slope portion of the area on which the box is planted?

Tom

That was my original thought last year when I decided to do a SFG but the ground where they're going is some serious hard rocky clay junk. I would need dynamite to loosen up the "dirt" enough to shovel it.