The compost you're adding each year is of course breaking down, and if you're doing no-till the soil is compacting somewhat over time as the organic matter breaks down. 10" of compost is eventually going to do the same thing, so I'd go for additional topsoil, or half topsoil and half compost.

Hi, Kristi - good to see you!

I would add a large fraction of fine sand (not from the beach [salt]) or (better) one of the fine Turface products for added water retention, and incorporate it. The mineral fraction will help to reduce shrinkage (and compaction) considerably and probably improve water retention. As the organic fraction, I think you'd be well pleased if you added fine redwood chips or the redwood mulch OHS (OSH?) sells.

Al

Hey Al, you're over here, too? I hadn't thought to use the Turface in ground. I figured that was mostly for containers. But come to think of it, now I recall you saying you use a modified 3-1-1 in your in ground plantings too. Hope the new year will be good for you. Thanks for the ideas.

The bulk mix from American Soil does have fine sand... which is why I was thinking more mineral content would be good at this point. You've given me something else to think about.

And thanks Tox.. that's another good option, one I might consider. That's the kind of answer my husband always gives... why not a little of both. :-)

kristi,
I was wondering if your soil is still above grade with all that skrinkage and how deep is the amended soil yet. If you are in a semi-arid area, do you need a high bed?
Still, I can see adding amendments whether they need them or not...I do!!

Hi Wayne, I can understand why you might ask. I'm in the Bay Area in California, and we have extremely dense adobe clay soil. On top of that, where my garden is, was heavily compacted for a year with a construction project and a big Caterpillar sat on the spot. And on top of that, the yard was used by a jeweler for 30 years, I slightly fear that he may have tossed some of his waste materials in the yard. And on to of that, we have bad gophers and moles. So we decided to build raised bed gardens with rodent cloth on it, and I like a lot of depth for tomatoes and other deep rooted plants, so I made them 2 feet deep. Now that I'm in my early 40s, (oh, my aching back, LOL) I can also see the benefits of a 2' tall bed so I won't have to be bending over all the time.

Obviously, the organic materials in the original soil has broken down and the soil has dropped. Now I'm just trying, after several years, to decide what material to use to refill my boxes.

-k

As the Soil Food Web digests, eats, the organic matter in your soil, and leave the mineral portion there, your soil will appear to "shrink". What you need to do is add, each year, enough organic matter to replace the organic matter they digest. As organic matter is digested the mineral particles move closer together which is what causes compaction, your soil looses its ability to retain air and moisture and plant roots have more problems moving around in search of those. essential nutrients are less available to the plants, too.
I would just add enough organic matter, compost or other materials, to replace the organic matter that has been digested by the Soil Food Web.

Hi Kimmsr, thanks for this helpful answer. This definitely puts the issue clearer to me.

Well I guess the soil food web has been hungry... LOL... usually I only need about 4 inches to top if off but this year I need almost 10.

So could you answer one more question for me? Would you just add the 10 inches as compost, and lay it on top and not work it in, or would you work it in a little? My concern is that since these are 2 feet deep and only 4'x8', there's not a lot of surface area for it to be in contact with the ground and I'm not sure that the compost on top will ever really make it down into the lower levels of the boxes without some intervention. At least not in a time that would be beneficial for my growing... and that is of course my primary concern.

THanks, -km

I would add soil, and keep topping it off with compost every year.

I guess maybe it would depend on the organic matter content and general health of the existing soil. If it's pretty good stuff you're in a maintenance phase with that, so it leans more toward adding soil to fill it up. What I'm getting at is I'm not sure you need to add 'as much compost as the soil food web can digest', if that is more than is necessary for a healthy garden. If the annual additions of compost were enough health-wise, even if the elevation was dropping, that points to adding more soil rather than just compost.

I agree that having enough basic soil is important...with compost added. That's why I am wondering how deep the soil is now.

Wayne, the (good, well amended sandy loam) soil I originally brought in and filled to 24" deep is now probably somewhere around 18" on average. These beds are sitting directly on a flat bed of my native solid packed adobe clay soil.

I'm guessing that directly underneath my nice richly amended boxes the densely packed adobe clay has benefited by having these boxes on top of it, but I made the boxes deep so that I had plenty of good loose amended sandy loam to grow in. I do grow 8' tall tomatoes, and I wouldn't be surprised if the roots of those grow down into the clay below the boxes, but most of my plants are probably staying in the boxes.

So as I said, the soil is probably about 18" deep now. A couple of the corner areas are maybe only 16". Basically, I'd like to get that back to about 24" of soil so that the soil fills up to the top edges of the 24" tall beds I built. In part it's aesthetics, and in part because I know that the boxes need their annual dose of compost topping. I was just surprised this year how much it has dropped. Maybe it's because I let the soil rest that the soil food web gobbled it up, I don't know.

I really do appreciate all your advice on this. I'm leaning towards my usual topping of compost, but bringing more of it in than usual, and mixing it down into the soil rather than just applying to the top. I use a gardening pitchfork for much of this work, and I try not to do this when the soil is wet. I know it's not ideal for the no-dig method, but I garden these beds pretty intensively so I suppose I'm leaning more to the "john jeavons" camp than the "ruth stout" camp, at least for this step.

thanks!
-kmama

Sounds like a plan to me. I too like to do some deep mixing.

Start by taking a good look at the soil you have and determine how much organic matter is in that soil. what you want is around 6 to 8 percent humus (the residual level of organic matter in soil) in that soil. Maybe these simple soil tests could be of some help.
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains� too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

Hi Kimmsr, let's just assume that I've already done the steps you listed below, and that I've determined I need more organic matter.

So I ask again, Do you blend it in? Do you lay it on top?

Do you use plant matter only?

Do you use animal manures?

Do you add nothing, if you don't can't find a reliable source of compost?

Thanks!

If the soil contained between 6 and 8 percent humus I probably would look for some mineral soil to add rather than adding more organic matter. Adding more organic matter could make the soil you have into a bog, someplace that holds too much water. Given your base soil is clay I would look for sand to add if I could at a reasonable cost, but the amount would be quite high and that might be cost prohibitive. The total amount of sand would have to be in the 45 to 75 pecent range.
Since animal manures can add fairly readily available nutrients I would not add them unless a good soil test showed the need, and then how much would depend on what was needed.

You have heard a lot of opinions on this, so I'll add my two cents worth. If this was my garden, this is what I'd be doing (and I am doing) this year. I'd add some more compost and work it in with a pitchfork. To me, there is a big difference between adding and working it in as compared to using a rototiller to completely mix and break things up. The "soil food web" is active in your garden and will continue to be.

In my garden I will also add/work in some mineral content such as Azomite to replenish what has been removed and used. I have 2 buckets of volcanic sand to mix in to add mineral content.

Last year I created a raised bed garden using 40 bales of straw as the growing medium (no frames, just planted in the bales) on top of my yard which is heavy clay that was graded from a farmers field. In February I placed the bales and added compost and ammonia sulfate to the bales to start the decomposition process. After 3 months, I added more compost, Azomite, volcanic sand and Axix to create the growing medium. I was quite happy with the results this season. Because the Straw bales are very porous, I added the Axix to help with water retention (baked clay, the same as Turface. I also seeded the bales with red worms to help create more compost and enrich my growing medium. When I added the remains to my compost piles this Fall, I was amazed by the amount of worms in the material.

Since you live in the Bay area, you might Google "growing your greens" and check out his videos. There's a lot of information about suppliers in the Bay area.

Thanks, Coach. Oddly enough, I stumbled on the Growing Your Greens guy this weekend when I was looking up Texas Tomato cages and I am blown away by his garden.

He mentioned the Azomite... I'll look into it. I'm wondering if I would need it, since my starting soil (this pre-mixed top soil that contains rock and sand). He is growing in 100% compost, so the Azomite makes sense.

Thanks!
-k

What exactly is Azomite? I haven't run across it here in the Midwest.

kimmsr mentioned adding sand and that it would require a huge amount. If you can find silt or silty sand, it's a better amendment to lighten the density of clay because you don't need as much to get past the concrete danger zone.

"What exactly is Azomite?'

It contains both macro and micro minerals.

Here is a link that might be useful: Here is Azomite

The link below, that Lloyd attached to another post here, might help some understand improving soil better.

Here is a link that might be useful: OSU on improving soil

OK so Azomite is a mined mineral, some type of rock dust, no organic matter. Just wanted to get a general idea what it was. Thanks.

Kimmsr, thanks for the link to the PDF. Very interesting and useful information. -k

Hey Kimmsr, so, I completed the soil in a jar test, and I was really surprised.

Where I thought I had a LOT of OM/compost, turns out there is barely any. I would say it appears to be 1% or less, in a very thin layer floating on the top of the water surface.

The rest of the results are harder to tally precisely because the sand and the silt overlap a little at their respective edges, but I can see a general trend.

Together, the sand and silt comprise about 70%-75% of the mix. If I had to assign amounts, I'd say it looks like:

Clay, 25%
Silt 25-30%-ish (depending on overlap with sand)
Sand 45-50%-ish (depending on overlap with silt)
OM, 1% or less

I also did the worm test and was shocked, shocked to find very few worms in the top 12 inches of the soil. I don't know if it's been the freezing weather (last week) or the biblical rainstorms (earlier this week) but I certainly was surprised by the lack of earthworms.

The drain test is a little difficult to do right now because we just had a lot of rain, but it appears to be draining faster than 2 hours.

So if I'm interpreting these correctly, I am in dire need of more OM, right Kimmsr?

I am wondering if the mix that I started (a purchased mix from a reliable local soil company) with was either too light on the OM, or perhaps the OM was not fully composted and the soil food web gobbled it all up?

Either way, it sure seems like I need some compost. STAT!

And I'm guessing that I WILL need to dig it in rather than just mulch the top.

And finally, after reading the PDF you posted earlier, I guess I'm not completely clear on whether to use a fully composted compost---which will provide longer term structure but not much for the soil food web, or a partially composted compost---which will provide more food for the SFW in the short term.

help much appreciated!
-kmama

PS. I guess the issue of whether I need Azomite in this mix is cleared up... there certainly seems to be a rather adequate mineral supply, right? What are your thoughts on Azomite?

The worm "test" is not factual, never was.

Worms can be an indicator of good soil but the absence of worms does not correlate to having poor soil. IOW, there may be other reasons for the lack of worms not related to soil conditions.

Lloyd

kmama, I am not Kimm and hope he will answer your question on AZomite. I have one garden that has been in gardens for 80 years and before that it was farmed. Another garden has been in gardens for 39 years and the third has been gardened for about 10 years.

I kinda assume that some of my gardens may be a bit short on some micro minerals...so I added a small/moderate amount of Azomite.

Azomite is simply more mineral, and with a soil organic matter level of around 1 percent you need more organic matter not more of the mineral component no matter the source. The results you got are the biggest reason why people really need to do soil testing.
Earthworms are an indication of the Soil Food Web in your soil. Few earthworms mean a not very large colony of other of the wee thingys that inhabit a good, healthy soil. Like all the other members of the SFW earthworms need organic matter to live on so they do not inhabit a soil lacking organic matter. Therefore, the number of earthworms in your soil is an indication of how healthy your soil is.

So as to not detract from the original topic, here is a link to a thread debunking the no-worms-equals-bad-soil claim.

Lloyd

If worms come and go because of a variety of factors, you'd have to look more than once in different weather and seasons to really know.

Anyway, organic matter it is, so go to it!

As far as the finished vs. active compost, I have had some delightful results from sheet composting around plants as they grow, as well as lasagne gardening where compost material layers are made within the soil column rather than just on top. If you do that just make sure it's a balanced mix, too much brown or green could cause problems.

But with that loamy mix, you've already got an excellent base to start with no matter what you do.

Oops, I think I misread the results, and my kids (unbeknownst to me) had shaken the jar again.

So after 18 more hours of sitting, the layers settled again.

Here's the new results:
What I thought was clay was really the silt layer.
The sand layer is now a little more clear, though there is still overlap.
The actual clay content is just a thin film on top of the silt.
And there is about the same amount of OM floating on the top.

So it's REALLY about:
-50% sand,
-48% silt,
-2% OM
-an almost non-existant amount of clay

So in a soil that is mostly sand and silt, is the goal still to have only 6-8% compost?

Thanks!
-kmama