I think it depends on whether this is an annual or perennial bed, and how you feel about adding more stuff in future years.

When I first built my raised perennial herb bed, it was small, and I made my own mix from bagged products, with a very high ratio of organic matter. My soil was GREAT, and the plants loved it...but it sank. And sank. And sank. I've been put in the position of needing to dig up well-established plants, some of which had become small shrubs, in order to lift them up and add more soil.

Now that I'm extending that bed, I'm filling the rest with plain old "topsoil" (or maybe the place I got it from called it "loam"?), especially since all I've been able to find in my area is 100% dirt or 50/50 dirt and compost. I'll add my own organic matter in more sedate proportions at planting time, and mulch well.

If you have a bed that you expect to turn over or otherwise completely clear out at the end of the season, and you don't mind buying more stuff to top it up next year, then a higher ratio of compost would be fine. Then again, if you get "just dirt," you'll need to keep adding organic matter every year, right from the beginning, rather than skating along for a few years on the excessive amounts that you might have started with.

I suspect you don't need anywhere near 50% compost for good results. I think people consider an ideal amount of organic matter to be more like 5-8%, and if the topsoil you're getting really is good stuff, as you suspect, it may well have some in it to begin with. You wouldn't know for sure without testing, of course, though you could do a crude "jar test" to get a sense of it.

In short, I have made the mistake of starting with super-high levels of organic matter. I regret it, and I say "never again," or at least not for a perennial bed.

You can't make your own "topsoil" but you can make (or gather) your own compost/organic matter. I'd order a higher percentage of soil (90/10 or so) with the plan to add my own OM in the future to keep it healthy.

Lloyd

Ok, so I should just go with a load of topsoil and then a smaller laod of compost? Fill 90% with topsoil, then add 10% compost and just mix in the top 30-40% with a shovel good and let the worms do the rest?

I do have a 2 pallet bin composting system which I plan on turning into a 3 bin system sometime soon. So yes, I will have annual compost to add every year, though some of my friends will have to buy thiers.

Also, can someone check my math... One "yard" as they sell it, is approx 3x3x3 in feet, or 81 cubic feet. Our beds are 4x10x1, so 40 cubic feet. One yard will fill two beds completely to the top. So for 10 beds, I'll need approx 4 yards of topsoil and 1 yard of compost. This will be closer to a 80/20 ratio, but it's close enough.

One cubic yard is 27 cubic feet.

Yea for some reason my calculator spit 81 at me and my feeble math brain didn't even consider that was way too high. LOL oh well, so I'll need 15 total cubic yards of material to fill 10 beds.

Thanks Pat

"I'd order a higher percentage of soil (90/10 or so) with the plan to add my own OM in the future to keep it healthy."

I second the motion.

The optimal level of organic matter in soil is in the 6 to 8 percent range, so starting with a mix of 10 percent compost probably is not a bad idea. Check your organic matter level annually to maintain it at that 6 to 8 percent level though.

Lloyd, sorry for calling you pat. LOL the pt03 and lack of your usual signature made me think it was someone named pat.

FWIW, I would do like Lloyd (90/10 topsoil/compost).

Then layer regularly with organic mulches from then on out.

I'm putting in some raised beds and I already have some soil but it's a 50/50 ratio of topsoil and compost that I used for my lawn. It would really be conveniant and I really don't want to have 3 piles of topsoil, compost, and a combination of the two.

I have a bed that the top 6 inches is all compost, does that mean my topsoil is 100% compost?

I believe soil has to have some percentage of sand/silt/clay mineral particles in order to be considered soil. That is just my assumption though, but I would say, no, the top 6 inches is just 6 inches of compost on top of your soil.

Also, I see what you did there. ;)

Just to throw in an additional wrench, I read a newspaper article on composting today which contained the age-old misconception that organic matter breaks down into 'beautiful black soil.' Sometimes they call it 'dirt'. No, it's not soil, it's organic matter. :-]

BTW... Coconut head,
81 Square feet is 1 yard of product spread out @ 4 inches thick. so..if you had a 4' x 20' bed, with 1 yard of compost ,you could cover the top of it with 4" of compost ;-)

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