Another option might be to put gravel under your sand. This can create a perched water table. Normally that isn't looked at as a positive thing but if done properly, you can use that perched water table to your advantage. It's a technique used in USGA golf green construction. Lots of folks, including "experts" in the industry think that the gravel under the sand is to improve drainage but actually, it's quite the opposite.
This site has a pretty good quick explaination.

It is exceedingly rare that I recommend people try to change the texture of their soil for a myriad of reasons. Since it sounds like you may have access to gravel, do give the manufactured perched water table some thought.

I am not sure that would work. The way I understand pnbrown, he has massive sand and is amending it with silt and clay to improve water retention. Wouldn't gravel just drain even faster? Unless he put clay under and around the gravel to hold water in. I didn't check your linke, maybe that's what the plan is.

As far as the original question, I think mixing silt/clay up to about 50% max should be fine. They say if you're going the other way - amending with sand - you have to get into the 35-50% range to prevent forming a type of concrete, so I would think you would want to keep it at least 50% sand for safety.

It is pretty counter intuitive, but the gravel underneath the sand actually stops downward water movement. The capillary action of the relatively small spaces will hang onto water more strongly than gravity can pull the water down into the relatively huge empty spaces between the gravel particles. For that reason, water will "hang" in the sand to an extent (more on that in a second) and remain available for plant roots. Think of putting your thumb over the end of a straw, pulling the straw out of a glass of water and watching the water "hang" in the straw. It's not a perfect analogy but shares some concepts.

You'll end up with a saturated zone about 1 or 2 inches in depth when you irrigate so the roots can access the water but the entire rootzone does not become saturated and anaerobic. When more water is applied, the gravity of the increasing hydraulic head will push the water into the gravel so you don't have to worry about over saturating.
If you google "USGA Green Construction Perched Water Table", you'll find all sorts of reading on the concept.

If someone wants to mix soil textures I can't stop them and sometimes it does work out but regardless of what anyone says, when you mix textures there is always a chance that you will end up with wide particle size distribution, which can lead to a tendency for the soil to compact. To do it without worry requires sophisticated testing, special equipment and experience. Also, it is very difficult to uniformly blend two soil types in the ground and you often end up with balls of silt and clay in a sand matrix which has its own set of problems.

Anyway, I ain't the dirt cops and anyone can do whatever they want. I just recommend looking into a strategy other than mixing soil types before making a decision.

pn, I believe that some silt and clay well worked into the sand so that it is all uniformly mixed will move that sandy soil more into the range you desire.

I have been working from exactly the opposite direction. I have good clay loam soil to start with. Still, it can be slow to dry out in the spring and could crust some. With the addition of about 30% coarse sand, 30% local sphagnum peat moss with black fines that make it very well hydrated, and 40% original topsoil, I have an extremely satisfying mix nearly a foot deep that warms up well, holds moisture well, drains and soaks up rain like a sponge, and is loose in structure. I love it.

I have never seen the dreaded concrete or adobe fear mongering happen here. Perhaps some clay with smidging amounts might not work so well.

"and you often end up with balls of silt and clay in a sand matrix"

That is a likely outcome in my case. I was thinking these would act as little moisture warehouses, so to speak, and perhaps minerals as well. Do you know any specific problems with this kind of situation? The beds where I am basically making two distinct layers are perhaps a different situation.

The perched water table thing sounds fascinating, and incredible. I will read up on it. No reason why I couldn't do a test run on a small bed here. Where it could really be a huge asset is at my florida place which is nothing but enormous amounts of excessively drained sand dozens of feet deep. Here I have the luxury of the pond fines as well as crushed glacial gravel being nearby, whereas down there there are no good sources of silt or clay sized particles in quantity that I know of. However there is crushed limestone rock which is the primary construction material. I was thinking about digging out beds and lining with some water-proof membrane, or almost water-proof, or some organic material that perks extremely slowly, but all of that would be more expensive than gravel-sized rock.

Off to read now.

What type of area are we talking about here? Are you looking to improve acres or just a modest garden plot?

Wayne, I can see already from the very small amount I have done that getting the stuff evenly mixed will be difficult. Or extremely slow, at least. The only effective way i have at my disposal to achieve it, that I could think of, is to dissolve the fine materials in a bucket of water and then pour over my soil.This gets a pretty even layer distributed on top with the finest particles penetrating the sandy soil to an unknown depth (by making a thick mix of this I can create a thicker layer on top which has already proved useful in helping to germinate seeds that are very difficult in sandy soil, like carrot).

Garg, how much coarser do you suppose the underlaying material must be in the perched water table system? I can get something that they label "stone dust" which is a range of sizes mixed together, freshly-crushed rock, most of which is a good deal coarser than sand. Nothing bigger than about 3/8". I already have an area where this stuff is in place and in fact i was going to try putting the sandy loam soil on top of it. Maybe I"ll try another test bed with 3/8" peastone under. Seems like anything like that would need the dust-barrier material between the layers to prevent the soil from eventually working its way into the gravel.

Forty, in my home garden here in MA it is a scale of a few hundred square feet of beds I am re-building, and a couple thousand feet of garden overall that I intend to amend with the water-pouring method with various types of super-fine material. Additionally I have another half-acre plot but can't afford the time or the material there. Same droughty sand, sadly.

My florida place is acres and the sand there makes the stuff here look like prarie gumbo.

Just a couple followups.

gargwarb, I see that the concept was not at all what I was assuming, and I know what happens when I ass - ume. :-]

I have had the concrete effect to an extent after adding a relatively small amount of sand to a heavy clay. So I can attest it does actually happen.

I don't think having clumps or clods would be a problem, and eventually with digging, freeze/thaw and worm action, they are going to homogenize into the soil just like everything else. If I was doing this on a garden-size scale, I might consider laying it on top and then tilling the whole thing.

Alternatively - and I did this once when I got sand in early summer and couldn't use it on most of the garden right away - take a fallow bed and build a lasagne compost pile with layers of the new soil between compost materials. Next season plant into the new layer or dig/turn/till. I got a great crop of sweet potatoes the next year and that bed is still the best texture anywhere in the garden because it got the most sand added.

Anyway just a couple of thoughts, but you may be going in a different direction already.

I feel your pain, pnbrown. We live near the southern shore of Lake Michigan and the native soil here is nearly 100% sand. Purdue did a soil survey in 1981 and denoted ours as "dune sand" and "unsuitable for agriculture."

Since you've had your clay/silt delivered already, it sounds like you're well on your way down that road. I'd be interested in hearing how it works out for you. When we first moved here I began adding copious amounts of compost and manure and encountered the same issues as you - namely, no matter how much was added, it couldn't hang onto any moisture. That's improved over the years, and I attribute the quality of my soil to two main additions: 1) pine bark fines; and 2) Turface. I was initially tipped off to these on the container forum and thought I'd experiment. I've been really pleased with the results. The benefits of these (vs. compost, manure, etc.) is they break down much slower, so they don't disappear into the sand as quickly. In fact, the Turface specs suggest a breakdown of 3% over 20 years. In other words, it's very durable. If you're not familiar with Turface, it's a calcined clay product that is used as an infield conditioner on baseball fields. It's also is similar to products used for soaking-up oil, like Napa floor dry. It can absorb/hold/release quite a bit of moisture and, with a cation exchange capacity of around 20, it will hold onto nutrients, unlike sand.

For a large area, it's relatively expensive ($8-$10/50lbs.) but it's a marvelous product and works well with sand.

Wow, somebody with sandier soil than me, sounds like. I would certainly make use of a wholesale supply of pine bark fines if there was anything like that here - we are on an island, so no major operation that would produce something like that. In truth we are lucky to have a gravel pit - the neighboring island of Nantucket used their pit up years ago and now has to import sand and gravel. Otherwise that load of silt and clay that I got for $160 would have been out of the question expensive.

Tox, I am not much worried about the clods either. In fact, when I dig planting holes whether for tomatoes or fruit trees or whatever kind of thing like that I think I will line the bottom of the hole with a thick layer of the fines to stop up the water.

In nature sand can be very good depending on the depth of the sand. If the sand is very deep, going beyond the root zone, it will run through causing the root zone to dry out pretty fast. In other cases there is a relatively shallow clay layer that stops the vertical travel of water. If this is within reach of the root zone or even a little below then the sand becomes a much better growing media. So given that you could mimic nature by removing a couple feet of sand and put in a layer of clay, then replace the sand. I would go ahead and mix the sand with as much organic material as possible while I was at it. Doing it this way would still allow the plot to drain out the sides.
Clay is is used often on these boards. Clay can have very different characteristics when compared. Some clays will take on moisture rapidly while others do not. Once some clays dry they turn almost rock like and stay that way until broken up, such as road grave. Others will take on water and hold it very well, making them very tillable when they have just the right moisture.
Silt can can have can have just as many variable depending on what settled out of the water it came from.
There maybe a local agricultural county agent in your area that can help you with this. They would be much more familiar with the clay/silt mix you are looking at using.

That "perching" problem/benefit is simply a gardening myth. The vertical change in permeability to a higher permeability with depth (e.g., sand beneath silt, or gravel beneath sand) simply slows a downward pressure wave or wave of higher degree of saturation (it need not be fully saturated at all). Retarding this infiltration for a few hours (in coarser materials, say sand) or even a day or so (in finer materials) hardly represents a perched situation and hardly adds to benefit (longer term soil moisture) or troubles (prolonged soil saturation).

Studies by soils physicists in the research area of stratified soils lead to a better actual understanding than those by horticulture professors. Unsaturated-zone hydraulics investigated by civil engineers lead to better understanding too.

But just look at the extreme, say pot-in-pot culture or other elevated air-pruning-of-roots growing method. The permeability of the air is essentially infinite. Do the elevated pots saturated at the bottom more than the trivial depth theory calls for in a transient event after each watering?

Oh yes, Nova, I am aware of the various benefits to sandy soils. I like them. I don't like the drawbacks. There is no clay layer in my profile. It is highly organic sand-based topsoil underlain by packed glacial till or pockets of more sand. The primary drought control is disturbing the soil as little as possible and keeping it well covered. I do not always succeed in keeping it well covered.

Upon more thought, the idea of putting gravel under my beds seems a lot like carrying coals to newcastle. When hilling potatoes or digging tomato holes I don't want to be bringing up gravel, I have enough of that in the subsoil as it is.

That "perching" problem/benefit is simply a gardening myth.

Have any studies handy? I'd like to take a look.

But just look at the extreme, say pot-in-pot culture or other elevated air-pruning-of-roots growing method. The permeability of the air is essentially infinite. Do the elevated pots saturated at the bottom more than the trivial depth theory calls for in a transient event after each watering?

Are you saying that the idea of perched water--even in container culture--is transient at best? Not a challenge to your statement, just looking for clarification.

Putting gravel under sands more akin to a french drain than a moisture holding system.
Gonebannas, "Studies by soils physicists in the research area of stratified soils lead to a better actual understanding than those by horticulture professors. Unsaturated-zone hydraulics investigated by civil engineers lead to better understanding too."
I can assure everyone on these boards that this is gospel. I have been working with the structural characteristics of expansive clay soils for over 30 years. I know a lot about it. But I do not know near what they do. They will even admit that have a lot to learn.

Not that sand needs any drains, french or otherwise, aye?

"Another option might be to put gravel under your sand. This can create a perched water table. Normally that isn't looked at as a positive thing but if done properly, you can use that perched water table to your advantage. It's a technique used in USGA golf green construction. Lots of folks, including "experts" in the industry think that the gravel under the sand is to improve drainage but actually, it's quite the opposite"

I have to say well said gargwarb, well said.

I know it won't work for lawns. For some odd reason the city of San Francisco decided to put a layer of clay on our natural sandy soil in at the dog park at stern grove. The reason was they thought that they would allow cars to park on the lawn during the summer concert season. It is the worst lawn I ever saw. It has huge bald patches and it is always wet. I don't think they let car park there either. We want them to take it out, but now they say there is no money. It's a huge muddy mess. Even weeds don't grow there. But, I found it was ok to mix in a small amounts of clay in my garden. Mixing it really well was the key instead of making a layer that blocks water. I hope this information helps, but I don't know that it will help you. I think I would just use something like a thick layer of redwood micro bark on top. It will keep the water from evaporating off the surface. It will stay wet longer.

Mastergardner; Would you happen to have a link to that info. I would like to learn more about it. I don't always know what I think I know. I will now try and eat my remark about the french drain.
And no I would never install a french drain in sandy soil. I have removed a couple that so called professional landscapers have installed in sand. One of which did permanent damage to a residential concrete foundation.

Tropical, a layer of clay "on" sandy soil is a very different thing from a layer under the soil. If you read what this thread is talking about you will find it is the latter, for the most part, or perhaps evenly mixed throughout the profile. It is true that I am going to use some very small thin layers of the stuff on top of soil for seed-germination purposes but in such a tiny scale that it will have no large-scale effect on the soil.

The perched water table idea is probably true, I see no reason to disbelieve it. Nevertheless, I won't spend money and large amounts of effort on importing a foot of gravel and putting it under my soil. Sooner or later the underlayment is going to get mixed into the upper layer, with gravel that would be a disaster, while with clay/silt it will likely be a benefit.

It is true that I am going to use some very small thin layers of the stuff on top of soil for seed-germination purposes but in such a tiny scale that it will have no large-scale effect on the soil.
I would advise against that too. (I know, I'm a total naysayer). But putting even a thin layer of heavy soil over sand can cause serious problems. It's very common for me to go out to diagnose a turf problem on a sand based sports field to find that they used un-washed sod that was grown on a heavier soil. The clay layer will only be about 1/4 to 1/2 inch thik but water has a hard time moving into the sand due to the textural interface discussed above. In those cases, they typically end up with a layer of wet soil that remains saturated for extended periods of time sitting on top of the sand. That little saturated zone goes anaerobic and promotes turf disease. It's called a "black layer" and it plays havoc on turf. Here's a little more about that from James Thomas in the Soil and Crop Sciences Department at Texas A&M University. (along with a little more discussion regarding soil layering and capillary action among other things.

But Garg do you think that is very comparable to a garden situation where a row of carrots are seeded into a bit of clay/silt on top of garden loam? When the carrots get pulled the clay will get pretty broken up not to mention the light tilling that will happen for the next crop. I am talking about a band no more than a couple inches wide.

Well, I'm not so sure now that you mention it. I was actually working on a couple of turf projects yesterday and when I saw the word "seed", I immediately was thinking grass. I've never actually seen somebody do that in a vegetable garden. It might not be as big of an issue in that situation. But, being the devil's advocate, I can imagine that layer holding too much water and the seeds/seedlings rotting before or shortly after they germinate. I don't know if that would happen or not, but it seems like there could be some potential. I suppose you could give it a shot and see what happens.

Oh, and reading your post again, if your talking about an actually silty or clay soil on top of a loam, the type of loam will make a big difference. You can have a sandy loam that is about 15% silt and clay, in which case, I'd be more concerned. Or you could have a clay loam that is about 60% silt and clay. In that case I wouldn't worry so much because in addition to gravity, the capillary action of the layer beneath would also help water move downward rather than perching.

http://www.envsci.rutgers.edu/~gimenez/Soils%20and%20Water-Laboratories/How_Water_Moves_in_the%20Soil2.pdf

A simple nontechnical explanation for what happens and probably how the myth of a perched (i.e., saturated, reasonably persistent) layer arose. Notice how he says "'nearly' saturated." Instead the process is the slowing of an infiltration pulse but without actual saturation. See also how a clay subsoil can truly perch water.

Go to Google Scholar and search on "stratified soil" to begin the search for more.

I'm not sure exactly what part you're saying is mythical. From what you've posted:

"Coarse Sand or Gravel Subsoil
Fine soil overlaying coarse sand or gravel subsoil must become very wet before water will move down through the large pours of the subsoil. Under these conditions, the overlying soil holds up to two or three times as much water as it would if the course subsoil were not present"

And that's exactly what I was talking about. The water "perches". It's not actually 100% saturated but it is water that is perched until you apply enough for gravity to suck it down into the subsoil. With proper irrigation management, you can perch the water where you want it and use that effect to your advantage.

Of course, that saturated zone (not actually 100% saturation but close enough for the girl's I go with, as my grandfather use to say) Will be bigger in a fine soil over gravel due to greater capillary action but it will still be there in a sand over gravel. You might have a 5 or 6 inch layer of saturation in a heavy soil over gravel and a 1 or 2 inch layer in a sand over gravel.

In the paragraph above that, your reference states (when placing a find soil over sand):
"When water passes through a fine layer and reaches a layer of coarse sand, it stops until enough water accumulates to nearly saturate the fine soil"

Note the use of the word "stops". Again, this happens when going from a sand to a gravel due to a difference in capillary action of the two different layers. Again, this is the effect that we use to "perch" water where we want to so the roots can get to it.

As far as a clay layer goes, you're right. You can perch water that way too.

"Clay Layer
When water reaches the clay, the very fine pores of this layer resist water flow. Although water does pass through the clay, it's penetration is so slow that water tables often build up above the clay."

In that condition, note that water actually moves but slowly rather than coming to a dead stop like it does when you put a finer material over a coarser material as discussed previously. However, your zone of saturation will be larger and you can't "push" water into the subsoil when you need to by applying a bigger head of water. It will just perc as slow as the clay will allow it to move and no faster. It's harder to control soil moisture that way.

Both of these conditions become less and less important the deeper in the profile the textural interface is but when the interface exists relatively near the surface, either by accident or design, it can be an advantage or a liability depending on intent and management practices.

("Or so the legends of yore go.", I suppose I should say)

So my beds where I am putting the clay layer under the loam is an example of the latter case from the above link.

Garg, thinking about what you have said regarding my seed-starting medium, maybe a better plan is to mix in some garden soil with it. The reason I didn't want to do that was to beat weed-seed germination. I guess I could mix in some sterile bought stuff but I'd like to not spend more money.

"As far as a clay layer goes, you're right. You can perch water that way too."

Nope, that's the only way you can truly perch water, with a low-permeability barrier. The high-permeability zone just increases the dampness directly above it but does not perch water.

Actually, if you review the link that you yourself posted, you will notice (as I pointed out in detail in my previous post and quite frankly I'm growing weary of having to repeat myself for crying out loud) that water movement will stop when it hits the coarse layer until enough is applied to counteract the capillary action of the more finely textured soil above. Water will only slow when it hits clay but continue to move downward.
As you stated earlier, there is still a lot to learn. However, those particular concepts are well understood.

If you sincerely believe that downward water movement can not possibly be impeded in the way that I've described...well...I've explained in detail how it works and the link that you yourself posted supports what I'm saying. I'm not sure what else to tell ya there, sport.

So my beds where I am putting the clay layer under the loam is an example of the latter case from the above link.

Maybe. It depends on how heavy the clay is and how heavy the loam is. I thought we were talking about sand though.

Garg, thinking about what you have said regarding my seed-starting medium, maybe a better plan is to mix in some garden soil with it.

That could work. Especially if the "garden soil" is primarily organic material. Lots of the bagged "top soils" are mostly organic with some sand mixed in. Or are you saying some of your soil? Either way, I think that would be the route I would probably go, given the choice.

By 'loam' I meant my garden soil, which is sandy with high OM content, about 11 percent. The pond fines material is lumps of many sizes some are completely gummy clay that is quite difficult to dissolve in water others are fine silt that can be broken up in the fingers with some effort, these lumps are mixed up with sand also, of course, since sand is ubiquitous at the gravel pit.

"will stop when it hits the coarse layer until enough is applied to counteract the capillary action of the more finely textured soil above."

That doesn't equate to perching. This being the whole point.

I have nothing against faith-based (myth based) hydrology and the intentional or unintentional changing of the meaning of technical terms in such an inconsequential realm as a discussion board, but to soils physicists, and civil engineer and geologist hydrologists, "'perched' water table" has a meaning and "this ain't it."

Ohhh..... So it's a terminology thing.
Perched water table is a common use term that in agriculture and horticulture has been "borrowed". Does it meet the strict geological definition? No, but in the that ag/hort world, that's what we say. Words are used differently from one discipline to the next and even within the same discipline.
For example, if I am in USDA mode, I would say that a soil mineral particle between 0.05 and 1.0 mm is sand. But when I'm in ASTM mode, I would say that anything between .074 and 4.76 mm is sand. The definition changes from one "little world" to the next. I just have to be fluent in both if I want to participate.

If that's what's sticking in your craw, I can understand that. However, you could just say "Hey, that's not the way they use that term in the circles that I travel in."
The concepts I've described and that you and I both linked to, are not a thing of fantasy or myth. They can result in benefits or problems just as I and countless others have observed and described. To say that the idea I presented is myth in the face of so much evidence is silly when all you meant was "I don't like your use of that term to describe the condition". I'd use an alternate term for it to help you feel better, but there really isn't one. In ag and hort, that's just how people describe that condition.

I could also understand if it was just me but that's not the case. It's whole industries communicating that way. If you want to communicate fluently in multiple circles, you have to learn the languages regardless of what you feel the first and true definition is. Going back to sand and gravel, I think calling a bucket of material that is bigger than 4.0 mm across "sand" is absolutley silly. Any reasonable person would call it a bucket of gravel. But that's ASTM and, when in Rome.....

I connot visulize anybody digging out the soil in a flower bed or garden and installing gravel. In the first place the gravel system is used in a golf coarse where the grass roots are all at the same depth. This is a highly controled and manupulated design for a specific grass. This flat out does not happen in a home garden with the highly variable root systems, water requirments, and nutritional needs involved, no matter how anybody defines perched, gravel or sand.
So far the best and simplest idea yet is what pnbrown asked about in the first place. The only thing outstanding in my mind would be the ratio of the mix and the properties of the silt and clay. The only 2 words on here that have any relevance as to definition are silt and clay.

I think the thing that pn desires for the very sandy soil is more body.

In my heavier soil I desired more looseness and permability in the upper layer.