Should I dig down and turn over the soil beneath the lasagna layers?
Should I drill holes into the ground and fill them with gravel?

First one IMHO is best. Gravel holes is for hardpan or heavy clay. If you don't have these, incorporate new into native ~4-6 inches.

Dan

I'm wondering what turning over a sandy soil will accomplish, unless you're turning organic matter INTO it. I don't think it would accomplish anything - I'm assuming your first layers were newspaper, cardboard, or something to choke the weeds/grass?

I'm also quite certain that the gravel-filled holes wouldn't help at all. Actually, Editornj, if you don't mind the crosstalk, maybe someone could tell us/me just exactly what the gravel-filled holes are supposed to accomplish in even a hard clay soil? My first impression is that it would be wasted effort, but I'm willing to be educated if there is something I'm missing.

I don't think you need to bother with the effort of mixing the lasagna ingredients into the new soil mix, but it does sound like a good idea - and wouldn't hurt anything. It just might make some of the nutrients in the ingredients that break down rapidly a little more readily available to shallow root systems.

Al

My first impression is that it would be wasted effort, but I'm willing to be educated if there is something I'm missing.

This is an old-timer's trick. It creates a sump.

Turning over mix into native soil avoids a perched water table.

Dan

This is an old-timer's trick. It creates a sump.

I thought that's what someone might say, but it's totally ineffective as a sump or reservoir. Of course you'll grant they would be unnecessary in sandy or loamy soils. In clay soils, during periods of heavy rain or saturated soil, water would simply move laterally into the holes and quickly fill them. They will not empty again until the water percolates through the soil. In order for them (holes) to be effective, they would have to drain somewhere (as into a tile that would carry water away). Look to the oft repeated advice not to backfill planting holes in clay soil because of the 'bathtub effect' for a corollary.

If the raised bed soil was saturated and the soil below reasonably dry, and the "sumps'" purpose was to help prevent over-watering, they would be superfluous. The water column in the RB soil would push down on the water and force the lower water laterally through/under the RB sides. The only water that would remain in the soil would be briefly perched water that would very quickly be removed by the wicking action of the more dense soil below.

Turning over mix into native soil avoids a perched water table.

This is actually not how it works. Since we KNOW the soil in the RBs are going to be more porous and comprised of larger particles than the soil below, water will not perch in this soil. Even the argument that a more homogeneous intermediate layer (between in situ and the RB soil) eases the transition between dissimilar soils would be moot because the finer soil below is in fact a spectacular wick and would exert an even stronger combination of gravitational + capillary pull when undisturbed, as opposed to when amended with the RB mix. In order for any water to actually perch in the RB soil, the lower strata would have to be comprised of particles at least 2.1x LARGER than the RB soil.

Additionally, digging into and amending the soil under the raised bed, if it is clay/clay loam, brings with it the surety that you would be, even if inadvertently, creating a 'bathtub effect'.

Al

Al,

I used to own a landscape business in Sacramento, and in the old clay soils commonly found there your options are raised beds or sumps or French drains (esp in high water tables). I don't recommend sumps as they are not very effective for the energy expenditure, but the Italian settlers used them as there was little else to do, and their olives survived. Anyway, my experience there taught me the effectiveness of various strategies. But sumps work a little bit if the fall of your yard is such that you can't make French drains work and you don't want a raised bed (for, say, lawns).

As for perched water tables, Your logic is incorrect and based on an incorrect premise:

Since we KNOW the soil in the RBs are going to be more porous and comprised of larger particles than the soil below, water will not perch in this soil.

Because there is a difference in pore size, the potential difference in the capillarity means that the column above must be saturated before the water in the pore spaces can 'make the jump' and move to the native soil. I did what seemed at the time interminable lab work as an undergrad to understand this concept. That is: soil moisture does not like to move to strata with different pore sizes.

Nonetheless, I explain this here a little bit. As I said elsewhere (link I can't find now), when I did tree hazard assessment and the tree was on a mound, I knew the new soil was not incorporated into native and the roots got too wet, the tree was under stress and pathogens invaded.

In other words, folks: incorporate new into native to ensure water moves thru the soil column into native soil.

Dan

Sumps might work marginally if the clay soils are not saturated, but expecting them not to fill quickly is like trying to dig a hole in the water (not the bottom) of a lake or pond. You confirmed my statement that for them to be effective the really need to drain 'somewhere', so no further discussion is warranted, unless you have something to add.

Sorry, but neither my logic nor my premise is faulty. Soil moves readily downward into strata comprised of smaller particles. One way to illustrate this - simply push an absorbent wick - it doesn't even have to be absorbent - a toothpick will suffice - into the drain hole of a container with a layer of saturated soil at the bottom and watch how much perched water is removed. The wick is precisely analogous to what a dissimilar substrate would be.

If soil is reluctant to move downward when the substrate is comprised of smaller particles, it is because of a slow percolation rate due to compaction (clay) or because the soil is already saturated. This introduces a 'time' element that is not part of the discussion. Our discussion is limited to whether perched water will or won't move downward into a substrate of finer particulates. It assuredly will. In fact, it will move downward into substrates that are even larger than the soil layer above, as long as the particulates are no larger than 2.2x (the 2.1 i noted above was a typo) the size of the particles in the layer above.

Not only is this proven science, but I've done dozens of various demonstrations in front of many groups that show precisely how it works.

It is not that "soil moisture does not like to move to strata with different pore sizes" but rather that soil is reluctant to move downward into substrates with particle sizes larger than 2.2x those in the upper layer. This is precisely why the water table in clay soils atop sand/gravel substrates can remain perched interminably while we never see it in sandy soils unless there is a bowl effect in bedrock or clay at work.

Even in a container, if you start with a soil that supports a 4" PWT and fill the bottom of a container with 4" of fine sand, it will pull ALL or most of the perched water out of the upper layer of soil. Of course I would never recommend using sand at the bottom of a container unless it was to prove this singular point.

Take care. Try the experiment.

Al

Thank you tapla.

First, the question was about sandy soil. Not being there to look at their soil, we must presume that the particle size difference is likely enough to be such that hydraulic conductivity is interrupted, as the surface tension changes across the gradient to the large pore size, thus the soil column above must be saturated to create enough pressure head to 'jump the gap' and break the Van der Waals forces in adsorption (surface tension to particles). So, going back to your first question, you are indeed turning the new soil into native, as I wrote above, in order to have more or less continuous pore size (or at least no distinct strata).

Second, having long experience with agricultural extension offices and tree-planting programs, one learns that absent visiting the site, one falls back on sound soil science to solve problems. The solution being an admixture of particle sizes into the native to ensure that pressure head created by saturation isn't needed. When we start explaining the details of your bolded text above, we often find the eyes of the listener glazing over and the message is lost; therefore it is generally easier to state that it is best to mix because different layers means you might not get drainage, and the message is transferred and acted upon.

This is, BTW, precisely the issue in many tree planting failures - too much OM in the planting hole, and surrounded by either clay or compacted soil of high bulk density (or a 'glaze' from equipment) - that leads to poor survivorship; that is: the planting hole is a 'pot' out of which the water cannot escape and the tree dies due to no oxygen in the soil.

Returning back to the point, IMO it is prudent and likely essential that the new soil be turned over into the native soil to ensure adequate drainage.

You take care as well tapla.

Dan

I'm going to make some popcorn and prepare a comfy seat, as I don't think I can contribute to this chat anything more than this:

Soil is 60% sand, 33% clay. A test described it as "brown, sandy loam. Slightly dry, subangular blocky, friable, slightly plastic."

Thank you for the information. I'm staying tuned...

Thank you editornj.

If you were to come to my counter and ask this question, the answer given by me and any Master Gardener and anyone with a soils or hort degree would advise you to incorporate your mix into the native soil to give a better chance at proper drainage, especially with sandy soil. Your % clay and 'slightly plastic' gives you a better chance at proper drainage, but this brief description changes nothing about what I wrote above.

You can also take your soil series (presuming the tech named it for you), go into your Extension office, and they can tell you whether you need a particular micronutrient. Usu these series have been analyzed enough for general recommendations for amendment. But nonetheless it is good that you are raising the beds - esp with Trex-type material - and making lasagna.

Dan

Dan - we're not talking about a better chance - we're talking about whether or not the raised bed soil will drain into sandy loam; and it's not "generally easier" to till organic matter into the soil (to promote drainage) if it's not necessary - it's easier NOT to. We cannot make the presumption that the sandy loam particles are LARGER than those in the RB soil, which they would HAVE to be to retard the downward migration of any perched water that might occur if the substrate was comprised of large particles. We KNOW that "the pot in trench" method of sinking containers into a trench filled with sand or native soil removes ALL perched water from the containers (that's why it is employed). There is no reason to believe something other than that would occur in a RB application.

The bolded text you referred to is a quotation of what you offered, not what I said, and I think my explanation and reason for the refutation was hardly cause for anyone's eyes to glaze over. It is a very simple concept.

As drainage is concerned, the facts are: There is no need to incorporate organic matter into the sandy loam/native soil below Editor's raised bed. It is far more likely to be harmful than helpful (bathtub). It will not ease the downward transition of water out of a media comprised of large particles into a substrate of smaller particles because the water will already easily make the transition unless the soil is saturated/prone to saturation, and if it is, we're full circle again to the bathtub, plus the water is likely (in nearly all cases) to be free to move laterally out of the raised bed as well. It cannot eliminate a PWT that is not there.

Al

Real quick as its late & I'm tired:
we're talking about whether or not the raised bed soil will drain into sandy loam; and it's not "generally easier" to till organic matter into the soil (to promote drainage) if it's not necessary - it's easier NOT to.

Not necessary?! Any farmer will tell you that they'd prefer deeper soil. You want your garden plants to have large root systems. If they are inhibited by impeded drainage and a stratum of lower nutrition, it is to your plant's benefit to fork under the yum-yums you made to have the roots go down rather than laterally.

Does the American corn belt have a layer of deep soil or shallow soil? Do I want good soil 12" deep or 24" after forking? Why do people bother to double-dig?

Bed time.

Dan

I think your shock @ "... we're talking about whether or not the raised bed soil will drain into sandy loam; and it's not "generally easier" to till organic matter into the soil (to promote drainage) if it's not necessary - it's easier NOT to." is unfounded. We are in a discussion about drainage here and not about whether it is an advantage for roots to grow deeper or not. We really should stay on track & not introduce new things to discuss. You really haven't refuted anything I've set forth so far.

If we must waver from the discussion at hand, I'll comment on root depths. Roots do not actually 'seek' moisture and nutrients. They grow where the soil has them in favorable volumes or ratios; they don't grow where there is inadequate air/water/or nutrition, and when cultural conditions change to unfavorable, they often simply die. Root growth is often a cycle of growth and dieback that changes, often dramatically, with cultural conditions. There is technically little advantage to roots growing deeply, unless it is to keep the plant from toppling or if deep in the soil is the only place water air and nutrients are.

In the case of your cornfield example, it would be an advantageous mechanism in times of drought, but in RBs, where nutrients, water and, air are found in abundance at the surface, it would be of little value. IF it was of any value at all, it would be in the fact that you 'might' not have to irrigate quite so often, but before you can call that an advantage, you have to 'assume' that roots would not grow into the sandy loam, and that is not the case. Additionally, even if deep roots WERE a benefit (this application), it could easily be offset by the consequences of what would occur when the amended hole fills with water - that darn bathtub thing again. What is the purpose of lasagna beds if not to avoid the tilling and enrich the soil via the work of soil biota - and avoid the bathtub? Why would this raised bed application be different?

I apologize for following you off topic, but the cornfield example is really not very applicable. We are talking about drainage issues and not nutrition, but I'm ready to leave either subject & allow the forum to decide on the individual merits of the arguments presented so far if you are. I'm also just as happy to hear anything else you have to offer & perhaps offer additional comment of my own - as long as the forum isn't getting bored to tears.

Al

Dan, tapla - this is good stuff! Just don't make me have to break you two up. :-)

EG

My arguments are not ad hominem - I think Dan's a pretty bright guy - an asset to any forum he would choose to participate in. I just think that in this case his arguments are not holding water. There's a pun in there, if you look for it. ;o) In the end, it will be you guys that decide.

Take good care.

Al

Hello Editornj,

I hope you had a healthy dose of butter and shared with the SO.

The fact pattern is simple to understand:

o building raised bed
o over sandy soil
o that presumably is not in frequently flooded part of property.

»The [implicit] questions were:

o should the OM being created be incorporated into native soil
o should the drainage of the site be improved?

»My recap:

o Turn the OM into the soil to improve structure and to avoid drainage issues.

The fill/mix will over time break down into smaller particles (unless physics and chemistry has changed recently). You want to ensure there is no chance of creating a pore size gap that has to be 'jumped', creating a (fill in your preferred term: PWT/zone of saturation/waterlogged soil) area that is less favorable for root growth.

»This is my advice, encapsulated in one bullet.

I can either trot out my credentials and experience to give weight and credence to this advice (and blow still more GW server memory with the replies), or

»I can state that I'm confident enough in this advice that if you were to take what I wrote to:

1) 10 Master Gardeners at your Extension office, 9 or 10 would concur, or

2) the old guy up the street who has lived there for 60 years and ask him if you should dig down to improve the soil for better veggies, he'll look at you as if you were daft and yell at you for being dense (and his wife will feel sorry for you, take you aside, pat you on the arm and say that "the deeper the roots the taller the plant" and then bring you tea and yummy chocolate chip cookies), and/or

3) several of the remaining farmers in the area. Ask them if they were offered two deeds for 2 truck farming properties nearby and, all else being equal, would they purchase the land with 12" of good soil or 18-24" of good soil. They all will take the nearby land with 18-24" of good soil.

»If either 1) or 2) or 3) occurs, I'll donate $25 to the charity of your choice (maybe not the 'daft' or cookie part exactly, but you get my drift).

No value in improving sandy clay {{gwi:492316}}. Danger of bathtubbing in sandy clay loam. Not relevant what the root depth is in veggie gardens. Come now. Sheesh.

I have deadlines. Let me know via e-m how the interview(s) turn out and which charity my $25 goes to (I have a PayPal account).

Dan

I think Dan's a pretty bright guy

Back atcha Al.

Regards,

Dan

What was wrong with the original questions, and why have we abandoned the original argument?

"Should I dig down and turn over the soil beneath the lasagna layers?" It's not necessary, but wouldn't hurt anything - unless the soil was clay loam to clay, in which case you run additional risk of creating a bowl that will fill with water and could kill roots if the water remains for extended periods. Millions of gardeners layer lasagna beds with no tilling. It also will not help to eliminate a perched water table. You are in no danger of water perching in your raised bed over sandy loam unless you're growing in a sludgy soil. All well-aerated RB soils will be free of any perched water over sandy loam as long as the soil is not saturated, and IF it is saturated, water in the RB can still move laterally across the top of the in situ soil or laterally through in situ soil as it dries.

Should I drill holes into the ground and fill them with gravel? We've abandoned this argument because it's been shown futile unless the water can be directed away from the bed via a tile, basin/pump, a ditch, other. They will quickly fill with water that moves into the holes both from above and laterally.
Should I put 4" Mel's mix on top, stir it up, then add more Mel's mix (this idea came from another Garden Webber -- thanks!)? I don't think you need to bother with the effort of mixing the lasagna ingredients into the new soil mix, but it does sound like a good idea - and wouldn't hurt anything. It just might make some of the nutrients in the ingredients that break down rapidly a little more readily available to shallow root systems.

I'm not sure why you keep arguing on about the point that mixing organic matter into the soil is a good thing. If you look at the very first thing I offered on this thread, you see I agree with you. Al says, "I'm wondering what turning over a sandy soil will accomplish, unless you're turning organic matter INTO it." You can clearly see that you're preaching to the choir. What I don't allow is that the organic matter helps drainage. Because the particles of organic matter are larger than the particles of the sandy loam, if anything it inhibits the downward movement of water.

You're not arguing against the science, Dan. There is no need to march out your credentials or experience another time. I'll only be impressed if you offer something that refutes anything I've said so far. Getting sidetracked by bringing up corn fields and what you think others might believe is really not much in the way of proof.

1) 10 Master Gardeners at your Extension office, 9 or 10 would concur I was a master gardener and rub elbows with them on a regular basis. I can tell you that all but one in 100 will not understand what either of us is saying. I have another presentation scheduled early in April to a MG group upstate, and the topic is Gardening in Containers. The talk will focus in large part on soils and how water behaves in containers. Before you say that soils in containers & in situ soils are different, I'll say I agree, but I think I've demonstrated a thorough understanding of the 'science applied' in both fields. I teach master gardeners.

2) the old guy up the street who has lived there for 60 years and ask him if you should dig down to improve the soil for better veggies, he'll look at you as if you were daft and yell at you for being dense (and his wife will feel sorry for you, take you aside, pat you on the arm and say that "the deeper the roots the taller the plant" and then bring you tea and yummy chocolate chip cookies) What do we care about an old guy who 'thinks' that deep roots make taller plants? How does that apply to this conversation? I suppose I would be as patient as I am here & explain that tall plants are the result of favorable cultural conditions and deep roots do not guarantee tall plants. I would then fill him in on the physiology to support what I said. Remember please - we're supposed to be focused on a scientific issue re. water movement through soils.

3) several of the remaining farmers in the area. Ask them if they were offered two deeds for 2 truck farming properties nearby and, all else being equal, would they purchase the land with 12" of good soil or 18-24" of good soil. They all will take the nearby land with 18-24" of good soil. How did we get into real estate? ;o) This is no argument at all. You're assuming that the soil below the RB in question is poor or that lasagna gardening will not improve it. That's a logical leap you cannot make. These are all all combinations of 'straw man fallacies', 'questionable cause reasoning', and 'confusing cause and effect'.

You accused me earlier of obfuscation, but I think you and the forum can see that I'm trying continually to keep you focused on the subject and to eliminate your extraneous arguments as they appear - it's not working. That you offer no argument that refutes anything I've said, I have to believe there are none forthcoming.

Just so there is no confusion, I'd like to say that I'm arguing against Dan's positions, and not the man himself. I don't harbor any ill will toward Dan.

Al

Ah.

Skimming the contextually lacking... interesting prolixity, I should have realized I needed to include a 4) in the wager:

4) Test whether basic principles of soil science continue to apply today, and construct two boxes in the same general area but sufficiently separated to ensure isolation and no mutual influence, where the first has no amended native soil, and the second has amendments forked under, crops and planting plan same.

The easily obtained comparative metrics being a) total water applied to each box, in gal. b) total yield c) per-plant yield d) individual plant height e) comparative taste (subjective). The result should be the forkin' box used less water, and had better yields.

»If any combination of individual or subset of 1) thru 4) occurs, I'll donate $25 to the charity of your choice (maybe not the 'daft' or cookie part exactly, but you get my drift).

Please notify me by e-m to which charity I send my money.

Dan (not taking anything personally)

4) Test whether basic principles of soil science continue to apply today, and construct two boxes in the same general area but sufficiently separated to ensure isolation and no mutual influence, where the first has no amended native soil, and the second has amendments forked under, crops and planting plan same.

The easily obtained comparative metrics being a) total water applied to each box, in gal. b) total yield c) per-plant yield d) individual plant height e) comparative taste (subjective). The result should be the forkin' box used less water, and had better yields.

But Dan - I already allowed in my very first post on this thread that incorporating organic matter into subsoils was a good thing. You can leave this point now. ;o) The point I made and what you vehemently disagreed with is that It will do nothing to eliminate a nonexistent PWT.

You: "Turning over mix into native soil avoids a perched water table."

Me: "This is actually not how it works. Since we KNOW the soil in the RBs are going to be more porous and comprised of larger particles than the soil below, water will not perch in this soil. Even the argument that a more homogeneous intermediate layer (between in situ and the RB soil) eases the transition between dissimilar soils would be moot because the finer soil below is in fact a spectacular wick and would exert an even stronger combination of gravitational + capillary pull when undisturbed, as opposed to when amended with the RB mix. In order for any water to actually perch in the RB soil, the lower strata would have to be comprised of particles at least 2.1x LARGER than the RB soil."

Then the discussion started. You have certainly not shown, by any stretch, that your statement is accurate, or that my statement is wrong in any way. All the 'arguing science' should have been focused on this point, but you ignore it, even after being prodded by me on numerous occasions to stay focused on the point of contention and not introduce all the superfluous arguments to help cover an unsupportable position.

Probably time for the jury to decide. I'm satisfied with the way I presented my case.

Al

Not that I want to interrupt the convo between you and Dan, but while I have you here Al, do you have anything to add to our earthtainer convo in this forum? SQFT gardening and container gardening share a lot of the same ideas about efficiency and such.

jleiwig - I agree....I'd like to get Al's take on the peat/vermiculite/perlite mix, as far as wicking capabilities. What say ye, Al?

EG

I'm not sure I want to (he pouts). After all, you guys already twice inferred I was rather sesquipedalian in that thread. I have no idea what you could be talking about. Lol

I'm joking, of course. Thanks for the invite. What should I do - just show up?

Al

Yep! If you have the time, please read through the discussion about the wicking properties of the peat/vermiculite/perlite mix, and share your thoughts on it. We're all getting ready to buy materials for our SWC's, and would like to know if this mixture will work well. Please?????

EG

Anyone with your experience is always welcome in any discussion on any forum as far as I'm concerned!

I'm looking for other options for my SWCs to make the best possible growing environment I can. I had read about truface and axis and such and I need opinions on them in SWCs.

I agree, even if I don't understand a word of it. Hehe. I hope one day to be one of the 99 MGs that doesn't have a clue or care!

Thanks for the help!

Not to sound like an a-hole, but rather to illustrate the practical implications of what I wrote above, this from another thread:
In spite of placing the bed on top of good gardening dirt, plants would often only root in the looser soil of the raised bed and not go any deeper.

There is a reason for this. It is well known, among many groups of gardeners and farmers (that I pulled out above). What didn't get discussed in-depth upthread due to prolixity avoidance is what I hinted at with the tree planting hole point.

I recommend reading the entire comment.

Dan

Posted by dan_staley USDA 5/S 2b (My Page) on Mon, Feb 23, 09 at 12:05

Not to sound like an a-hole

TOO LATE!

Regardless of the soil beneath a 12" box, unless the parameter of the box is sealed somehow, the laws of hydraulics will make it drain. Even if it is setting on top of a swamp, it will not wick more water than it can use. In fact, it may be an ideal situation.

John

The question is: how fast will it drain, and if it is slowly (making a saturated zone), will the roots go down? Nonetheless, had I done a better job at constructing my argument, I would have in the same comment listed all the numerous reasons to go deeper with your amendments, as the other thread pointed out. Roots don't like to work harder than they have to and if crossing textures is hard they won't do it.

Dan

Thats the reason I like to keep my worms well fed. ;o)

John