That's a good question. There is a current theory that says that once a garden bed is established, it shouldn't be 'tilled'. Tilling would include rototilling, spading, and turning. Once the bed is in good shape, it should only be top-dressed with compost and other organic supplements.

The idea is that a so-called soil food web becomes established. Fungi, arthropods, protozoa, bacteria, earthworms and other organisms are continually conditioning the soil. The soil develops a structure and that structure is vital to the health of the community of organisms living in the soil.

So, short answer, only the very top of the soil can be disturbed without invading the soil food web.

so does that mean it's kinda good to not mix compost in?

Raised bed gardening presents a very different situation from gardening in the ground, so the maxims that are associated with inground gardening do not necessarily apply. It's more of a hybrid between container gardening and inground planting and one needs to incorporate some of the principals that apply to both. It will not adversely affect the soil-food web to mix in additional compost in to the bed - the incorporation of compost or any other organic matter is going to be bringing in soil organisms and the "soil-food web" is going to be far closer to its natural state in the soil underneath the raised bed soil than it is the imported soil mix anyway. And if the raised beds are used to grow vegetables or other annual crops, just the activities of planting, weeding, cultivating and harvesting on a routine basis will cause whatever you apply to the top surface to be mixed in anyway.

Your compost is constantly being absorbed into the soil through the actions of the microbes, earthworms, the rains, etc. I see no harm in mixing finished compost into the top couple of inches of soil by whatever means you see fit. Usually on my double-dug beds, that involves mixing it in with a steel garden rake.

And as noted, it is only a "current theory" held by some that soil should never be tilled. There are others, such as the Bio-Intensive or French Intensive methods, that have a demonstrated history of very high yields while building the health and quantity of soil in the beds through a program of careful tilling of the soil. That tilling method is double-digging, a method of loosening the soil to a depth of about 24 inches while maintaining the layers of the soil. Mixing compost into the top few inches of soil is perfectly acceptable, is in keeping with the methods I adhere to and puts the compost and its nutrients at precisely the level where it can be of the most use to the roots of your plants.

The "soil food web," in my opinion, is not a system that once disturbed, is ruined forever. My experience using double-digging over the last thirty years or so has never indicated any problems with the "soil food web." In fact, it is only recently that I've learned from folks on forums like this that by disturbing the soil in any way, from double-digging to raking in compost, I've "destroyed" the "soil food web."

I guess that since I never experienced problems with yields and the tilth of my soil and the quantity of organic matter in that soil visibly improved each year, I never gave much thought to the "soil food web" that is all the concern today. My purly unscientific opinion, based on thirty years or so of double-digging raised beds, is that those who claim the "soil food web" is "destroyed" by the act of disturbing the soil in any way are ignoring some basic "instinct" of that very same system to regenerate itself rather quickly. My observations indicate that careful and sensible tilling practices must only cause a mild interuption of the "soil food web" that apparently, it quickly overcomes because no evidence of harm to the soil or productivity is evident.

Keep your soil layers in the same relative position, as is accomplished by double-digging, and the "soil food web" will very quickly re-establish itself. So mix your compost in, but not too deeply. And don't lose sleep over the "soil food web." (Unless you're a soil micro-biologist.)

Wayne

For raised beds, I'm somewhere in the middle. I use a combination of my natural rather sandy soil mixed with compost and basic soil amendments (alfalfa meal, dolomite lime, wood ashes, bone meal, etc). When I top-off the beds (once a year), I stick the spading fork in six or seven inches deep, wiggle it and open the soil without turning it, then usually add a cup or two of amendments, and mix them in the top few inches with a 4-tined "claw" just to get most of it off the surface.

But I also don't like to interrupt the microbial activity too much, so I try not to do it on a warm, sunny, or windy day, when exposure to sunlight and drying air probably would reduce the microherd somewhat.

If I could do this in the fall, I might just scatter the amendments on the top of the existing soil, top with compost, then cover that with leaf or straw mulch (or a combination of both). But that usually just doesn't happen once our rainy season hits.

The bottom line: do the best you can with what you've got, what seems to work best for your conditions.

Sue

MCW (Mountain Curmudgeon Wayne) and Sue both get a VoR!

Lloyd

P.S. Looked at your website MCW, lookin' good man!

Over time, as the soil bacteria digest the organic matter in the soil that organic matter "disappears", is actually converted to other forms of energy like plant nutrients and for that reason organic matter needs to be replenished regularly. Over much longer periods of time the mineral portion of your soil also will "disappear" but you seldom see that happen, but organic matter does and the more active your Soil Food Web the faster your organic matter will "disappear".
Your raised beds were all organic matter, no mineral soil, except the vermiculite, added according to what you wrote so you will see a "loss" of volume much more than someone that has 50 percent mineral mixture in those same sized beds.

+1 to kimmsr's post, to which I would only add that you may want to consider amending the soil mixture with 15-20% more vermiculite by volume.

I'm building a set of raised beds and current had it in the plans to use 33-40% vermiculite, 20-33% peat moss or coco-coir (if I can find it cheap enough) and the rest being my homemade compost.

** I know there is a current heated debate over the continual use of peat moss and the fact that it's technically considered a non-renewable fossil fuel... but at the moment it's currently 1/10th the cost of coco-coir by volume

no need for peat or even coir in most cases, we start our beds using spent mushroom compost from the farms, that comes as cheap as. in some locations there is coposted recycled green waste available from the refuse sites somethimes it is free to residents.

no difference to the plants between raised beds and tilling the soil realy, at the end of the day it is all growing medium and the raised beds make gardening easier as there is no tilling or disturbance to the soil structure, can't realy see the connect between raised beds and container gardening? as container gardening is a whole 'nuther process.

simply adding the compost in a layer on top works fine, cover it well with mulch and the worms will do the digging work.

we don't do composting at all all material gets composted in the garden beds in that above manner, that includes all rottabe kitchen scraps. save a lot of work and the need for a composting position in the yard.

len

Here is a link that might be useful: len's garden page

Thanks to all for the input---it's appreciated

I think I messed up bad. Someone advised me to make a potato bed out of peanut hulls...nothing else. They advised they knew all about it, and it produces an abundance of potatoes. I did and also covered the bottom with liner, to prevent weeds from pushing through. But after reading this, I may have nothing but mush. HEEELLLPPP!

g'day moidene,

mmm not sure about what you may get it could work very well in the end?

check out our pics of our instant potato patch. we get a 5:1 return ie.,. plant 1 kilogram of spuds and get 6 kilograms in return.

len

Here is a link that might be useful: len's garden page

complete layman here. don't know anything about the soil food web and since i have to a dig a hole to plant my tomatoe plants i dig it big enough and deep enough to make them happy. so i guess by digging a hole would i not be disrupting the soil food web? doesnt make much sense. i have to plant the planst so i have to dig up the dirt. hmmmmm help me out here guys and gals

Thanks for the picks Gardenlen. That is an impressive yield in such a short amount of time. My concerns are just with the peanut hulls. They do have a little soil in them, not alot. The bed is about 8 ft long and 3 ft wide and 24 in. deep. I added a bit of potting soil mix yesterday to it, just to help. I wasn't given clear directions on what to do. I do know it's staying nice and moist (not wet) and warm inside the bed.
I really hate to use chemicals for insects or anything. Do you use chemicals of any kind, or do you let nature take care of it??

You can also build a "build as you grow" potato bin. Basically it allows you to add 3" of soil on top of the vines each time they reach 4" of length, continually burying them as you go. As you run out of space in the container you simply screw on another board and add more soil.

Then, at the end of the season, harvesting is nothing more than unscrewing one side of the panels and harvesting as you pull them down. I've heard of yields being close to 50lbs out of a single 3'x3'x3' box in this fashion.

Here is a link that might be useful: Build As You Grow Potato Bin...