Shop Products
Houzz Logo Print
novascapes

The Myth of Soil Amendments

novascapes
12 years ago

I found this while doing some other googling. Thought it was interesting. Just don,t know how factual it is.

http://www.sustainablehorticulture.com/myth-soil_amendments.pdf

Comments (74)

  • novascapes
    Original Author
    12 years ago

    "novascapes...'native crappy soil'....lol. Does yours deflect a shovel like it's made of brick? "
    Actually, when dry, I use an electric jackhammer, Only because I use them in my business. If I did not have them I would be using a pick.
    I agree with the article as to trees because of the soils I deal with. If I was always in control of the water then it might make a difference. Trees take most of their nutritional needs from the top layers of soil. The fertilizers placed on the yard are usually adequate for their growth. When comes to flower beds and gardens then I feel I can control the drainage in the root zone because they are simply much smaller. I can amend the entire root growing zone.

  • californian
    12 years ago

    Where I live in Orange County, in southern California, my problem is not enough water. Any bathtub effect would be a benefit to the plant or tree. So far this year we have had a total of 2.44 inches of rain since July 1, a period of almost six months. For some reason in California they measure the yearly rainfall from July 1 to June 30, probably because we get most of what little rainfall we get in the winter. My clay soil gets so hard no roots can grow through it except maybe for a few months in the winter if we get enough rain to soften it up. I too have to use my Bosch Brute 66 pound electric jackhammer with a clay spade to dig holes anytime of the year except maybe during the rainy season. I try not to buy dwarf fruit trees as my clay soil turns any tree into a dwarf. The only trees that grow at all are the ones where I dug big holes three feet wide and amended the soil. Trees that I didn't amend the planting holes stay the same size. I have a fig tree I planted five years ago and it only grew six inches in that time because the soil is so rock hard. The only time I get growth spurts is in the few rare years when we get maybe 18 inches of rain. My problems are made much worse because I live on the side of a hill which makes it impractical to water large areas as the water just runs down hill on top of the dry clay which actually repels water until it gets softened up by some drenching rain, which almost never happens. I also build berms perpendicular to the slope to try to trap rainwater so it soaks in. Rainwater is precious because it is not all full of Colorado River salt like what comes out of our faucets and builds up salts in the soil which will eventually kill most plants. I think the few brief growth spurts we do get is after a heavy rain some of the salt gets leached out. If I dig down about two feet I hit Caliche which is all full of thick veins of some white substance which when I first saw it thought it was dinosaur bones but later realized it was salt and carbonates deposited after many years of watering with alkali water.

  • gonebananas_gw
    12 years ago

    If I had really hard soil or shallow subsoil I'd be tempted to rent a DitchWitch for a day and criss-cross the area with 4-6 inch-wide trenches as deep as I could reach. I'd plant at the intersections and give roots at least four directions to go with relative ease. I think I have seen this recommendation elsewhere for groves, perhaps for exposed soft limestone or hardpan or caliche soils.

  • toxcrusadr
    12 years ago

    I am just amazed that I have been landscaping in clay soil for 20 years here, and have bought scores of plants, shrubs and trees from local nurseries, and no one has ever told me not to amend. In fact the (admittedly generic) labels on the plants and trees have little pictures showing the process: 1) dig, 2) amend, 3) plant. :-\

    I did find early on that digging DEEP holes in the clay and planting things below grade thinking they would collect more rainwater was a dumb idea. Lost a few small trees that way the first year, in the spring rains. The locals recommended planting HIGH and mounding up soil around the root ball to encourage drainage. That seems to work.

    I am really torn about amending now, since some of you are heavily against it for clay, but the stuff sucks so bad, I just don't see how a new tree has a chance.

  • Michael
    12 years ago

    Gonebananas: your comment about a Ditch witch reminded me of the "soil" in a region south of lake Okeechobee, FL. You want to see some bizarre agriculture, they grow tropical and sub-tropical fruit trees there on the Marl ground. What is Marl? Marl is a flat, ancient limestone sea bed, to stand on it you would see a tiny bit of what some might of as soil, under that very thin veneer is flat limestone extending form many square miles. So how does one plant trees in a smooth rock surface, with a ditch witch of course? The trencher cuts trenches north-south and east-west making a grid, at the grid line intersections the trees are planted and the rubble from trenching shoved back in the trenches. The tree roots can only grow down the rubble filled trench lines as they are unable to penetrate the trench floors and walls.

    If you think that's weird, you ought to see the commercial tomato fields where the rows consist of piled up Marl rubble, a drip irrigation line run down the middle and plastic mulch over the top. The trellis system is a real hoot too, a specialized machine is used to ram lengths of rebar into the Marl for the strings to be tied to. Tomato transplants are then planted in the beds down the bed middles.

    Soil amendments, what amendments?

  • gonebananas_gw
    12 years ago

    Actually I have seen those, years ago. I didn't see a regular trencher being used but rather a "rock plow" in front of a huge D-9 Cat dozer, where the plowed limestone rock was thrown up on both sides just in time to be run over by the steel tracks and ground-down further. I have seen pictures of the dozer with the rock plow in back and the Miami Limestone is so soft I'll bet a special trencher can penetrate it as you describe. Small migrant farm children in those tomato fields used occasionally to fall down the open drilled wells in the limsetone and then there were huge mechanized rescue efforts to trench down next to them. Elsewhere, some of that marl down there is naturally silt soft though and can be dug or plowed normally.

    I was thinking more though of the trenching through hardpan (some black ones exist in SW Florida, Bh horizons) or caliche (e.g., Texas).

  • Kimmsr
    12 years ago

    When we first moved here, some 40 plus years ago, there was hard pan in the sandy soil which did create problems with drainage. Hard pan is creatged in soils by chemical reaction, mostly iron oxides cementing soil particles together which is most likely why it generally is reddish in color.
    How I cured that problem was to add lots of organic matter to the soil.

  • gonebananas_gw
    12 years ago

    I occasionally encounter the expression "plow pan" (or something similar) for a hardpan that developes just below normal plowing depth in agricultural fields in some types of soils and occasionally have seen mention of deep-cutting "chisel" plows for breaking it up.

  • Michael
    12 years ago

    There are definitely chisel plows out there of many sorts, how they are set up depends on the job to be done and the soil conditions.

    Here is a link that might be useful: A chisel plow pic..

  • strawchicago z5
    12 years ago

    I live next to a limestone quarry. My soil is hard-rock alkaline clay that I almost broke a large shovel. I amended ALL MY TREES with very coarse builder sand (cheap), free mulch, and blood meal. I used peat moss for acid-loving plants. I also added tons of leaves and grass clippings from the neighbors. Here's my garden this year in hot July - I don't water my garden and I don't fertilizer either. The ones that get pampered are my roses (Not shown here). Now my trees are taller than 2-story house.

    In later years, I got sick of digging into the hard clay that I ordered a big pile of dirt. It was cheap alkaline clay, but at least it's fluffy, and helps with drainage since all plants are raised on additional soil. If I had done this before we would not had broken a heavy-duty rototiller with the rocks and hard clay.

    {{gwi:318133}}

    {{gwi:318134}}

  • gonebananas_gw
    12 years ago

    The chisel plows (or ripping plows, I see now is a term) I saw in photos before were more like this. (I'm still laughing at the lady.)

    They go so deep that only one or a few can be pulled.

    www.soilyourself.org/2011/01/deep-ripping-soil.html

  • Kimmsr
    12 years ago

    "Plow pan" and "Hard pan" are two different things caused by very different actions. "Plow pan" is the compaction of soil due to consistently plowing at a certain depth over a long period of time. Seldom will the color of the soil that is "Plow pan" be different from the surrounding soil.
    "Hard pan" results from a chemical reaction in the soil that results in the soil particles binding together. Most often this is from Iron Oxides and that does result in a reddish colored soil, although it can be from other soil chemicals and be other colors.
    "Plow pan" can be "cured" by varying the depth you plow, or following the no till concept don't plow, at. "Hard pan" needs work on the soil, correcting the chemical makeup, to "cure". Most often, I have found, the simplest way is to get sufficient amounts of organic matter into the soil.

  • jolj
    12 years ago

    Here in central South Carolina, we use a chisel plow in hay fields.The only other chisel plow was a 5 chisel, 36 inches long, that is also used to turn rocks to the surface in rocky hill country.
    In the planted fields we cut 4-6 inches with disk harrow, then turn plow 12 inches deep, then re-cut with the disk harrow again. You now have 10-12 inches of tilled soil.
    You can add amendments at anytime after the first cutting.
    All the farmer I know have used compost consisting of vegetation & manure, on their fields.
    Farmers in N.C,S.C. & Ga. I have known use amendments in the fields & in any plantings of shrubs & trees.
    I think amendment will not hurt, you need water, loose top soil & sun light.
    Planting too deep is failure, watering too much or too little is failure.
    I am planting trees this week end.
    I will cut up a 24" X 36" plot with compost & dig down 36" in the center of the bed.
    I will water the center to settle the loose soil after mixing in compost to hold water(sandy soil here needs no drainage.
    The trees (bare root Live Oaks)will be planted at grade, with a small berm to hold water.
    Never plant a tree below grade, it would be better to set the root ball on top of the ground( which is not much better).
    A friend planted bare root & all his trees died back to the ground, they are now shade trees.
    We will see if my plan works better.

  • gonebananas_gw
    12 years ago

    In the SE US lower coastal plain, the most distinctive hardpans are spodic horizons (spodosols) that can be nearly black in color, even though iron (and even calcium) can be abundant along with translocated organic matter (which itself perhaps moved downward in solution rather than particles). Radiocarbon dates on the organic matter can be in the thousands of years and certain horizons are several yards thick, though most are much thinner, a foot or less. Really interesting soils.

  • jolj
    12 years ago

    spodic horizons or spodosols.
    I am not familiar with this hardpan.

  • gonebananas_gw
    12 years ago

    If you look in ditchbanks in Horry County you commonly can see it -- a very dark layer below the light-color sand. I remember seeing it starkly on a road to and near the Grand Strand Water & Sewer Authority (near Conway I believe). It occurs widely though.

  • jolj
    12 years ago

    Conway, are you a Sun worshiper?
    Thanks, gonebananas.

  • pnbrown
    12 years ago

    That iron oxide hardpan layer is common around here. It doesn't seem to help much in keeping moisture in the sandy soil above it.

  • jolj
    12 years ago

    How deep is it?
    Can one break it up or is it too thick?

  • the_virginian
    12 years ago

    In my experience, adding a moderate amount of organic matter to the native soil with some fertilizer when planting has always resulted in better growth and healthier plants. The key is to make sure you never remove any of the native soil when amending and backfilling and to make sure the hole surrounding the root ball is deep and wide enough. Problems arise when the native soil is removed and backfilled with too much organic matter in too small a planting hole. Good mulch and watering well after planting is a must along with yearly fertilizing to give the root system a boost to break into the surrounding soil with vigor.

  • coconut_head
    12 years ago

    I watched a documentary where a guy said he poured regular old hydrogen peroxide, 2 quarts worth around the sides of the planting hole to chemically loosen the clay and then he planted the trees with no amendments, and backfilled with the same clay he dug out of the hole.

    Prior to doing this he had planted many trees by heavily amending the hole and most or all of those trees died or underpreformed. All of the trees he planted the second way survived and thrived.

  • pnbrown
    12 years ago

    I think it averages about a foot thick, maybe more. Be very difficult to reach with a chisel.

  • TheMasterGardener1
    12 years ago

    Coconut_Head,

    I believe it! Add that to the list of the many uses of hydrogen peroxide. Sounds expensive though.

  • hamburglar1
    9 years ago

    Old but interesting thread...

    What makes me chuckle about the research literature is to constantly see reference to "bathtub effect". Even when I started out in early gardening and dug holes too small and way over-amended, I have never seen anything like this in reality. My sense is that it was observed somewhere in some study, and then the echo-chamber in horticultural circles made a boogey-man out of it. I don't doubt that it is a risk, but I doubt it anywhere near as common as the literature and articles make it seem.

    I have clay soil and amending makes breaking up the back-fill soil a lot easier. But I always plant young container trees/shrubs, dig an extra wide hole (>5X diameter). Not nearly as experienced with B&B. My typical method with yard trees is to spread a 10-12' diameter ring of leaf compost in order to kill the turf/weeds ~six months before planting so the turf roots disintegrate. The backfill naturally gets mixed with the leaf compost and if the soil is really bad, I will fork the compost in over the full 10-12'. Estimating that it works out to 20% compost in the main hole. I'll top dress / mulch with the same leaf compost the next couple years, and then start rotating in pine bark as a mulch. I've never lost a tree and I've found that it allows for more efficient watering because there is less run-off or water re-direction than when I'm dealing with 100% clay.

    One case where amending has most definitively helped me is with slow-starting tree/shrubs. At my old house, I planted several sets, such as fothergilla, ginkgo, and nyssa, with both amended and non-amended holes (not a formal experiment - did not always have compost handy). Pretty much across the board, the amended versions started putting on decent, new growth 1-2 years before the un-amended versions.

  • Laurel Zito
    9 years ago

    Hydrogen peroxide causes cancer. They did studies of women who used hair dye and in particular black hair dye and they have more cancer, and hair dressing who dye people hair a lot have more cancer, even if they don't dye their own hair. I think it has to do with breathing it in, not with contact on the head, but I could be wrong, of course.

  • toxcrusadr
    9 years ago

    Good grief. For one thing, peroxide is not volatile, so inhalation is out. Also, there are many many other chemicals involved in hair bleaching and coloring. You said yourself, the rates were higher with black hair dye. What does that have to do with peroxide bleach? The best that could be said (if the studies you quote are true) is that perhaps hairdressers are exposed to 'something' in the workplace that increases cancer rates. And hopefully they factored out other causes such as smoking rates, age, gender etc.

    I seriously question what positive effect peroxide would have on clay. Really, as a chemist, it's a serious question because I've never heard of it and I have no real idea. The first thing it would do is chew up organic matter, if there is any, which seems like the last thing you would want to do.

  • Pyewacket
    9 years ago

    "What makes me chuckle about the research literature is to constantly see reference to "bathtub effect"."

    Well, Chuckles, I have seen multiple examples of "the bathtub effect" and I can vouch for its reality.

    Perhaps you are particularly naturally talented and thus have not seen it first hand yourself - but "I've never seen it" does not equate to "it doesn't exist".

    Have you ever seen a Blue Whale in person? A mongoose? Wombat? Tasmanian Devil (and I don't mean in a cartoon)? How about a lamprey? Vampire bat? Cane toad?

    I'm sure there are many plants and animals which you have never seen in person, yet, nevertheless, they continue to persist in reality, with or without any sign of recognition from you. LOL!

  • toxcrusadr
    9 years ago

    There are lots of people who had troubles with plants, changed the way they planted them, and things improved. Including me. The explanation makes sense. Good enough for me.

  • Laurel Zito
    9 years ago

    I have never dealt with clay, but I think the whole theory would only work for a larger plants. If one is growing pansies, it is very easy to dig a nice big hole for them and add a lot of compost. If planting a tree, there is a problem, you can dig the whole only so big and the roots are not happy and then you can have a lot of rain. In fact we are having historical rains. Then if the tree wanted fast drainage, there could be a problem with drainage, hence the bathtub effect. But things like vegetables are very much improved by compost even in clay.

  • Pyewacket
    9 years ago

    Compost worked into the soil is great - compost is an excellent soil conditioner. Compost dumped into a hole dug into a heavy clay soil - usually not so helpful.

    Decades ago I used to do the whole cover crop - soil amendment - double digging thing trying to improve my heavy clay soils. Then I started mulching and discovered the worms will do the work for me if I just leave them alone and let them do their thang with the mulch. Saved me a lot of wasted effort, LOL!

  • toxcrusadr
    9 years ago

    I started doing the same with clay, after early tillings to get a head start. Thick layers of shredded yard waste and wood chip mulch on perennial beds, and leaves/grass/partially composted stuff for garden mulch. I hardly use the Mantis anymore.

  • jimharper
    9 years ago

    So the categorical answer is that I should just plop my bareroot tree into a hole dug in the previously uncultivated adobe rangeland that is my backyard? And that's the same answer if I happen to be growing on three feet of prime topsoil in Iowa? Not hardly.

    You have to use a little horse sense. Very few things in gardening are a panacea. You want your plants to get off to a good start. Sure they grown out of their hole pretty quickly. But that first year is important, is it not?

    The practice as recommended by the better nurseries around here is to put a bag of cotton slash in the hole. That seems reasonable. If you heavily mulch as you should in my cold, arid climate, the soil wil change pretty dramtically in about four years anyway. At the other extreme, trying to turn the planting hole into something like a giant geranium pot isn't smart either. I've done that to my regret as well.

  • hamburglar1
    9 years ago

    I don't doubt that the bathtub effect exists, I just think it is less common than threads in this site (and some literature) would have you believe. A lot of people come here for advice on tree/shrub problems and invariably, a responder will pop up and try to scare/shame the original poster about how they should not have amended the planting hole. Just think it is overstated, that's all. In my area, most of the local nurseries and the local arboretum recommend mixing ~20% compost in the backfill.

  • gery
    7 years ago

    Dear Californian, Do you still look for 55 gal. potable water barrels? I am in the Irvine area looking for someone to take 6 of them. thanks. Gery

  • tsugajunkie z5 SE WI ♱
    7 years ago

    Dear gery, Californian has not posted since 2011.

    tj

  • gery
    7 years ago

    Thank you.

  • toxcrusadr
    7 years ago

    Craigslist free section is a great place to gift things like that.

  • gery
    7 years ago

    thank you.

  • jolj
    7 years ago

    I test the ground that I am planting in:

    1) if I can not push my straight finger into the soil to my palms, then the ground needs to be tilled.

    2) I till at least 48 inch square & add compost.

    3) I plant the tree in the center, mulch & water.

    4) no need to add compost to the hole, because the feed roots will move out into the square bed, which is a) the main reason for tilling & composting the bed.

    b) the second reason is to plant day lilies, iris or ground cover around the tree, which will benefit from the tilling & compost.

    If by chance I can push my hand down to or passed my palm, I do not till just rake up the square & put down the compost. Plant the tree & mulch & water.

  • lingon
    7 years ago

    Sorry if this is the wrong place to ask, but I have planted two peach trees and they died, I assume, due to the bucket effect - I see standing water in the hole for the whole spring time. So it seems that the native soil method would work better. I have clay soil that turns rock hard when it's dry and forms clumps that are hard to break up when wet. I have a shovel and my human labor. So if I want to re-plant my one surviving tree, how do I back-fill the hole with native clay? I can dig a hole by letting a hose drip on it for a few days until it's moist enough to dig. But then I have big balls of clay that won't fit around the tree roots.

    I also have a raised bed vegetable garden and I wanted to try mixing clay into one of the squares but I can't envision how to actually mix clay into the mel's-mix-like medium that is currently in the square.


    Thanks!

  • jolj
    7 years ago

    All clay needs is compost,compost,compost.

    My soil is sandy loam, but I have seen country that is red clay for miles, with a field that is clay that is black as smut. The gardener turned chicken & cow manure into the clay with other organic matter until his clay became soil.

    He also truck farmed his left overs from the garden & made a decent living for years

  • toxcrusadr
    7 years ago

    lingon, I had the same problem when I first began planting trees in my heavy clay. I planted some BELOW the ground surface with a DEEP hole underneath filled with amended soil. I did everything wrong. Some saplings up and died on me.

    The hole should be more of a dish, wider than it is deep. You want a few inches of amended soil under the root ball but not much. Break up the unamended clay below that to form a transition zone. Finally, the final elevation of the top of the root ball can be several inches above the ground surface. For potted trees, as much as 1/3 of the root ball can be above the surrounding ground level. Mound up soil around it and then mulch over everything. If it is hot and dry where you are, make a berm around the tree out where the mound reaches ground level. This way if it rains a LOT, water will drain off the root ball a little better, but when you have to water, the berm will still retain water.

    I have had pretty good success with this method here in MO. I also find that trees do better when planted in the fall than in spring where it can get very hot and dry in a hurry. I've even planted bare root trees in a big pot for the summer just so I could plant them in the fall. I don't lose trees to weather and soil anymore.

  • lingon
    7 years ago

    Thank you, never thought about the wide vs deep issue. This is all making sense and very helpful, but--

    How physically do I amend the clay and break up unamended clay? When I dig a hole I get clumps of clay. When I add compost, I get clumps of clay that sit in the compost like rocks. Years later they are still there. The worms (the very few I find) seem to just go around them. I can replace the clay with compost, etc, but I haven't had any luck mixing clay with compost, unless I form a slurry.

  • Embothrium
    7 years ago
    last modified: 7 years ago

    You should either excavate and replace the clay with more agreeable soil or dump it on top of the clay and plant in it, without mixing the two together.

    Or you can try the more tedious method of mixing coarse sand with the clay, to produce a permanent change in its texture. Drawbacks to this approach - in addition to all the mixing involved - include a large volume of sand often needing to be used before a useful change in the texture of a clay soil is produced, resulting in a mountain of finished soil being generated, and also the possibility of excessive drainage being created (voice of experience here on that one).

    Finally, you definitely do not want to work a clay soil when it is wet.

    Chalker-Scott's publications on garden and landscape soil management are right on - except where she says roots of plants in amended holes go around in circles because the amended holes are more pleasant for them. Actually roots always grow vigorously away from the center of the plant unless stopped from doing so by uncrossable barriers such as pot walls. Or the recently planted specimens are in too poor of a condition at planting to produce strong root growth. The main drawback to amending of planting holes or small beds is how the movement of water into and out of the amended zone is affected. This is the usual cause of reduced growth after planting in amended holes, when compared to that of plants in unamended holes. Organized trials using control plants to provide a basis for comparison were producing a consistent result (less growth in amended holes) by the late 1960s - this phenomenon has been known about and reported by horticultural practices researchers like Carl E Whitcomb for at least 48 years.

    Dr Carl Whitcomb

    http://www.drcarlwhitcomb.com

  • toxcrusadr
    7 years ago

    Definitely avoid digging it when it's wet. I know what you mean about the clumps though. There is a fine line between 'rock hard dry' and 'too wet to work'. I just take the time to put the excavated soil into a wheelbarrow and chop it with a shovel until there are no chunks over a couple inches in size. Then mix in compost. The volume will be more than the original of course, but if you're planting 'high' as I described, you will need extra to mound up around the sides of the root ball so that no roots are exposed.

    After you've dug your dishy hole and taken out whatever you are going to take out, chop the bottom of the hole a bit to break it up but leave that broken clay in place. When you add back the amended soil, there will be a transition zone that is part amended soil and part clay chunks. This will allow the roots to ease their way into the clay, as opposed to a sharp transition from amended to dense clay.

  • lingon
    7 years ago

    Thanks, I need to figure out the right moisture level to dig. I guess I've been erring on too wet, since it's impossible to do anything with when dry. I have a 5-year old peach tree that is maybe 5 feet tall and has a main branch die every year, but has been producing tiny delicious peaches, planted too-deep in a hole that fills with water in the spring. (It was a volunteer from my compost.) Is it worth re-planting it correctly? (Just considering plant stress, not my labor)

    Thanks again, I really appreciate all the help.

  • PKponder TX Z7B
    7 years ago

    I'll probably take a bit of criticism for this but I've gardened in soil (black gumbo clay) like you are describing. My solution was to liberally apply plain, cheap, not-antibacterial dish soap over the area a day before you want to dig. Spray it all down with the water hose to really soak the soil. This allows you to actually dig the next day without huge clumps. Once you hit the point that you are finding clumps again, apply more soap and water and give it a day. I think that this helps with mixing the compost in for a more permanent soil amendment. I have no idea of the reason that this works but I had favorable results.


  • lingon
    7 years ago

    That's really interesting to think about! I'm assuming the surfactants/wetting agents like sodium lauryl sulfate made the water 'work better' to moisten the clay. I personally would feel much happier using castile soap. But it doesn't work as well in hard water as SLS or other detergent surfactants. A quick search brought up someone using fabric softener for the same reason, and it seems there may be actual chemicals sold labelled for this purpose.

    Anyone out there tried castile soap to loosen clay for digging?

  • toxcrusadr
    7 years ago

    Question is how much soap are you using per square foot? Would it work better to dissolve it in a bucket of water and apply it evenly? I think so. I have been known to wet dry clay to make it easier to dig, but usually that's not for planting, more like post holes and such.

  • PKponder TX Z7B
    7 years ago

    I'm sure that mixing would improve the formula :-) I use about an ounce per sq foot, don't really measure. I cook without recipes too.


    I use Lemon Joy or something similar, I like lemon scent :-)