Question on Soil for raised bed

10 years ago

last modified: 10 years ago

Per suggestions to my earlier post here, I dug 4" of the ground soil inside the raised bed and mixed pine mulch ground barks.. I am just confused what should I fill the reminder of the bed?

I was planning to fill with "Costco's Whitney Farms 55 Quart Organic Planting Soil For In Ground use" (OMRI Certified Organic with Kelp and Alfalfa Meal.) See picture below. But the Instructions says, it needs to be mixed with native soil. My bed is 16" in depth, so I can't dig so much of the ground soil to mix. I called Whitney Farms, but the person was not sure. She communicated that If i don't mix the Organic Planting Soil with the ground soil, and instead use it 100%, it might choke the plant

So I am trying to understand what exactly should I fill the bed? Should I buy Top soil instead?

Thanks for your help

Featured Answer

digdirt2

10 years ago

First, you'd never use 100 percent compost to grow in. It lacks minerals, needed salts, creates root problems for the plants, and drains poorly.

Soil-less mixes do not compact like soil does but they are much more than just compost. They are composed of peat, perlite, bark fines, lime, and in some cases compost. It is all in the proportions of each. Soil isn't a bad thing when it is well mixed and balanced with other not soil ingredients. Folks who garden in ground still have to add all sorts of soil amendments to get it just right. That's why bulk mixes from nurseries work. They used big mixers like concrete truck mixers and measured components.

But the bagged soils like Miracle Grow Garden Soil, and apparently the Whitneys, have to be mixed with other things to work - they say that right on the bag. And you have to do the mixing and get the balance just right. For example, you could use the Whitney Farms bagged stuff IF you could also mix it with the right amounts of peat, compost, composted manures, perlite, bark fines, peat and enough lime to balance the pH. But most don't have the ability or equipment to do all that and to know they got it right. Plus it is very expensive to do.

This is a heavy lesson in soil science and grossly over-simplified. It is discussed in much greater detail over on the Soil & Compost forum here but you don't really have time to learn now all you need to know to fully understand it all as you need to get the bed filled with "something" and planted. So as Sey said, if you can, buy a good quality pre-mixed fill in bulk. If not and you want to use the Whitneys then the minimum is 1/3 Whitneys, 1/3 top soil, and 1/3 compost with some composted manure and bark fines mixed it. Not ideal but would get you started.

Dave

PS: in your other post didn't you show soil-less potting mix too in the photo? If so then I would add it to the mix too.

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Comments (6)

Seysonn_ 8a-NC/HZ-7
10 years ago
Love Trees,

Good progress. What to fill in, is a question of costs. For a big job I get some good garden mix ( top soil + compost ..) . That will be like 70%. Then I add some more manure ( steer, chicken, horse, cow.) and maybe some packaged raised bed mix, like you already found. I have used Kellogg Raised Bed stuff. It was pretty good ( $9.99 / 3 cf) and steer manure /compost from HD (~$1.50/1 cf). I even mix in some fine pine bark mulch. ($2.25 /cf). Or how about some peat moss ?

There are many combinations.

Sey
digdirt2
10 years ago
Sounds like it has the same problem as the bagged Miracle Grow Garden soil - if it isn't mixed in well it compacts. If so then I'd avoid using it. Can it be returned? I agree with Sey that there are less expensive ways to fill a raised bed. Buying a quality mix from a local nursery or landscaper is best. But as i said in your earlier post that all depends on if you can get it delivered or have the ability to haul it.

If not then bagged mixes is the only option. Many are available but soil-less mixes, compost, and composted manures work best rather than "soil".

But either way please keep in mind that as was discussed before when discussing filling the bed, the pine bark is supposed to be mixed in well with ALL the ingredients you add to the bed and not used just as a layer on the bottom.

Dave
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Love Trees
Original Author
10 years ago
last modified: 10 years ago
Thanks. Just found that a local company can deliver 1 Cubic yard of organic compost for 165$. With the extra 6 bags of pine bark i have already, this should fill in the bed completely. I will return the Costco Stuff back. Costco just discounted it today by 2$ to 7$
Richard Brennan
10 years ago
"My bed is 16" in depth, so I can't dig so much of the ground soil to mix..."

I don't understand your limitation on ground soil. You have unlimited ground soil to work with, don't you? Nothing is stopping you from rototilling your bagged soil amendment into a foot of exisiting soil if you want. The planting mix + the bark + the air you are incorporating is going to raise the bed level several inches. Mission accomplished. Keep adding mulch and compost on top and in a couple of years the bed will add even more elevation. The best part of taking it gradually like that is that the whole soil ecosystem will be coming up into the raised bed. In other words, don't think of it as adding a whole store-bought soil structure on top of the native dirt. Rather, you are building up and improving your existing garden soil, with all the soil life the comes with it.
Love Trees thanked Richard Brennan
Randall__UT
10 years ago
On another Garden Web forum posting, Hudson___WY(3) details what he uses very successfully in a greenhouse with 24" high raised beds:

http://forums.gardenweb.com/discussions/3219849/brandy-boy-contest-2015-5?n=173

The details are about exactly at the midpoint in the postings, look for a green Compost and Manure Mix photo. Only 10% soil, with rest being peat moss, vermiculite, coconut coir, compost/manure and other nutrient additives. Very light mix that seems to produce extraordinarily well.
Love Trees thanked Randall__UT