How much of what mix? If you have it available, just plain old garden soil will work perfectly well. If you need to import soil, purchase a garden planting (not potting) mix. Or if you need to create your own mix, proportion it to 75% mineral soil ('topsoil') and 25% organic matter (compost/composted manure).

Oh I meant was how many bags of compost, how many bags of top soil, do I need vermiculite or peat moss?

If we go by volume, which is what your suggested items imply, then you'll need about 4.3 cf of each type (13 divided by 4). Out of the 4.3 cf for compost, then you'll want about 0.86 cf each of 5 different compost types or products (4.3 divided by 5).

Adjust accordingly if you are filling up the bed to different depths, unless the 13 cf is already the depth you wanted.

If you are trying to do Mel's mix, then you can use all 1/3 as compost or you can have a mix of compost and soil if you want to vary it slightly, but those two together will be your 1/3.

You need no vermiculite or peat moss in a raised bed garden. If you follow the traditional 25% organic matter recommendation, then you need 3 and 1/4 cubic feet of compost and 9 and 3/4 cubic feet of topsoil.

This is NOT brain surgery.......you do not have to be exact! Round up or down as necessary to accommodate bag size. 1.5 cubic foot bags of compost is common in my area, so I'd go with 2 bags and call that part good & fill the rest with topsoil or whatever.

A 4 foot by 4 foot by 1 foot raised bed would be 16 cubic feet and most of the bags of soil I have seen have about 2 cubic feet so 8 bags should fill that bed, more than 6 but not quite 7 2 cubic foot bags would fill that. The optimal amount of organic matter in soils is in the 5 to 8 percent range, 25 percent is too much and can cause too much moisture retention.

Kimmsr, please provide a link from a university on that magic number for a raised bed. You may very well be right, however, I've also been growing in beds for years, and haven't been able to determine that magic number to satisfy my own curiosity.

Different levels of organic material have provided very similar resluts, with no problems in a raised bed. It seems like there is a range, and it is more likely to vary according to each micro-climate.

I think GardenGal's general advice on the subject is pretty dern good, until it can be rigorously determined, otherwise. My own trusted advisor says more organic matter than 8% in a raised bed is appropriate, yet concurs with your numbers for flat soil.

M

My hunch is that gravity will overcome drainage issues in a raised bed, and vegetables, for example, will grow better with higher organic matter than is appropriate for flat soil. One can observe that in nature, at the very surface of the soil, organic matter can appraoch 50%. M

In my own experiments with planting trees, I have begun planting the bottom of the root ball on flat surface, and creating a raised mound with soil that is around twenty percent organic matter. I have ripped out the tree after a year or two later, and have observed zero circling, girdling roots.

It has been observed, that when amending holes dug out for trees (subsurface soil), that amending the soild beyond 5-8% is well known to cause the roots not to leave the amended hole, which will often cause the eventual failure of the tree. My experiments with planting trees above ground appear to contradict this well known rule of thumb. M

kimmsr, from my earlier source on raised bed mixes:
"Also, your local climate may dictate a different mix than that required by someone in a very different climate (if you live in rainy Seattle, you will want a mix tailored to drain wellâ¦if you live in arid Arizona, you will probably want a mix that retains moisture as much as possible)."

... maybe you live in a wet land, and moisture retention is "risk" more than opportunity ... but I've had about 10 days over 85F so far this year ... so I'd check out where the OP is from, rather than recommend a blanket rate for the whole country.

Here is a link that might be useful: perfect

Mackel, here is one. I have, In the past posted numerous links that give that same information.

Here is a link that might be useful: soil composition

kimmsr, that link does not work, but guessing by the title, did you find a raised bed study?

Or are you suggesting that raised beds only aspire to general soil quality?

I can share this: "Several types of amended soil mixes can be used, but usually include good topsoil and organic matter often in similar portions. This gives you a planting mix that drains well and is easy to till."

That is from Kansas State University Research and Extension, PDF link below.

Here is a link that might be useful: RAISED BED GARDENING

This post was edited by johns.coastal.patio on Sun, May 18, 14 at 11:56

Please be more clear, Kimmsr., I do not understand what your post is saying. Is the link a raised bed study, or is it not? M

In most raised beds the soil mix need not be any different than what a good healthy soil in a non raised bed would be, 92 to 95 percent mineral (the sand, silt, and clay particles) and 5 to 8 percent organic matter. But then Pat Lanza has had very good results growing in her Lasagna beds that are all organic matter and some places make raised beds that are high enough that people with wheel chairs can easily work on the beds while in their chairs and some use a normal soil mix while others have opted for the soilless mixes.
I have never in my life had enough extra money to purchase what I needed to make planting beds and scrounged almost everything I did need, most often on the way home from work so little extra vehicle fuel was needed.

"In most raised beds the soil mix need not be any different than what a good healthy soil in a non raised bed would be, 92 to 95 percent mineral (the sand, silt, and clay particles) and 5 to 8 percent organic matter"-

again, Kimmsr, you may very well be correct (for example, Michigan, yes, Arizona, no). Have you done comparative tests yourself, or can you provide a link?

Making the assertion repeatedly does not satisfy other, experienced posters' curiosity. as it doesn't appear to concur with a number of authorities on the subject.

M

Here is a link that might be useful: Logic

"I have never in my life had enough extra money to purchase what I needed to make planting beds and scrounged almost everything I did need, most often on the way home from work so little extra vehicle fuel was needed."

I think I see where you are coming from now, and I can agree with the spirit of that. Efficient gardening is about using low cost, or free, local resources.

If someone has soil on site to make a raised bed, raised row, or simply an improved garden plot, that's ideal.

The thing is, there is this big bunch of people trucking in everything. When they are "buying by the yard" a yard a 50:50 is probably a good deal, and a safer bet that a product someone claims is 90:10.

Many people use 50:50, it works, and by the yard it's pretty cheap.

But sure, do any ratio of soil to compost before buying pallets of bagged potting mix (or ingredients) for a raised bed.

Mackel, I have worked in gardens and with soils in many places throughout the United States, Texas, Oklahoma, Tennessee, Ohio, Indiana, and regularly correspond with people in most all of the other states as well as many countries around the world, Ireland, Germany, Spain, Israel, Japan, and each and every time have found and hear that the addition of organic matter, in the range of 6 to 8 percent, makes a soil that would barely grow anything into a soil that will grow almost everything.
If you start with Sir Albert Howard and continue with a few of the real organic proponents they might be able to help you.

If you have found this to be true, then there ought to be numerous publications that concur. It's not a trick question, Kimmsr, not at all. It's simply how "science guys" are trained to roll... M

Here is a link that might be useful: Logic

This post was edited by Mackel-in-DFW on Tue, May 20, 14 at 10:42

Ah Mackel, let me point out that people such as Eliot Coleman, Lee Reich, Ann Lovejoy, Rebecca Coles, Keith Baldwin, as well as Sir Albert Howard, Friend Sykes, Lady Eve Balmour, and many others that do not come to mind right off have said pretty much what I have said here for years. Even Jeff Gillman agrees with adding organic matter to the soil.

Re- Raisbed Beds:

The subject, Kimmsr, is, what is the 'magic number' for the percentage of organic matter in a raised bed. Please provide a link. There appears to be wide agreement, that for a non-raised bed, it is around 5-8%.

M

Here is a link that might be useful: Logic

Hi Kimmsr,

Are you ready to concede that you simply make up stuff on this forum?

M

Proverbs 11:2-

"When pride comes, then comes disgrace; but with humility comes wisdom."

Old Testament