Mixing peat moss and lime to balance the pH?

gamebirdFebruary 18, 2009

I'm filling up a raised bed and a month ago I got a bale of spagnum moss for free. I also have as much agricultural lime as I need. My basic topsoil around here is nasty fill dirt with a pH around 5, so I don't really need the peat and certainly not as an acidifier. The local soil is why I'm using raised beds. I am wondering though if the moss might be useful as a filler and if I could neutralize or counteract its acidity by adding lime. What do you think?

I'm using other stuff in the bed, like horse manure, horse bedding, leaf compost, a bag of uncomposted leaves, and some topsoil. I don't need to use the moss in it, but I've been trying to think of a good use for it.


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Since we know that Oak leaves and Pine Needles do not have a significant affect on soil pH why would another source of organic matter, peat moss, with a higher pH affect soil pH? As long as you have that non renewable resource anyway go ahead and use it because I've seen my soils pH rise from 5.7 to 7.2 a year after the addition of peat moss.

    Bookmark   February 19, 2009 at 7:12AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Yeah I'd skip the lime too. You want to keep in on the acid side of the line anyway and any soil with adequate organic matter (peat qualifies) mixed in will revert to close to neutral with time. Too much lime tosses it quickly into the alkaline side and that is more difficult to fix.

For what it is worth, the Sq. Foot garden method recommends 1/3 peat for growing in and those advocates claim it works fine.


    Bookmark   February 19, 2009 at 10:22AM
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Make sure you thoroughly pre-soak the peat before incorporating it into the plot, otherwise it is very water repellent.

    Bookmark   February 19, 2009 at 10:35AM
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tapla (mid-MI z5b-6a)

It depends on what fertilizer you'll be using. If it's a soluble product, the odds are greater than 10:1 that it won't contain Ca. I would add lime to the raised bed soil in your case. The reason is because until the media pH equalizes at somewhere above 6.2, any lime will be in reactive phase and very unavailable for uptake. After the lime has a chance to react, any residual lime becomes more available. If you were incorporating it, the buffering effect of the mineral soil would be such that lime might not be necessary, and once roots grow down into native soil, it should be less of a problem if there is adequate Ca there.

Particle size of the lime and what kind of lime it is is very important to reaction times. Do you know if your lime is dolomitic (Ca+Mg) or hydrated lime [Ca(OH)2, aka calcium hydroxide]?

Example: Often when we make our own container & raised bed soils, and even when we add lime, the first tomatoes often have BER. You'll find that if you make your soil a few weeks ahead so the lime has time to react in the soil, that you can avoid the BER. It's the principle at work that I just described.


    Bookmark   February 19, 2009 at 1:45PM
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I don't know what the lime is, just that I was told it was agricultural lime. My father got a dump truck load and said I could have as much as I wanted. It has the consistency of... oatmeal (quick oats, not the full size type)? Builder's sand? Farina? Cream of wheat? Something like that. It doesn't taste like much (and yeah, I tasted it).

I don't plan on planting for another couple weeks. How much lime do you think is appropriate to add, if I should add some?

    Bookmark   February 19, 2009 at 8:00PM
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tapla (mid-MI z5b-6a)

If it is calcite limestone and doesn't contain Mg, or if you don't know what it is, I would pass it by. Ca applied without Mg in a favorable ratio (around 4:1, Ca:Mg) can create an antagonistic Mg deficiency. Dolomitic lime is cheap @ $5/50lb or so, and what you want. I would use that (dolomite/dolomitic/garden lime) in powdered or prilled form @ 5 lbs/ cu yd or 1/3-1/2 cup/cu ft.


    Bookmark   February 19, 2009 at 9:45PM
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Agriculture lime is ground limestone. If it was quarried from your area you should have no problem with using it. Most agriculture lime is local lime because of the cost of trucking. I see you are from Oklahoma. What area would be a help since the red dirt area would definately use the peat for adding humus if nothing else. You can adjust PH as it ages.

In other parts of Oklahoma you may have other problems such as Galena and zinc.

    Bookmark   February 20, 2009 at 12:27AM
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What you need to know is what caused that soil pH. Is the Calcium/Magnesium in balance? Too much Ca and not enough Mg or the reverse will affect what is going on. Agricultural lime can be either Calcitic or Dolomitic lime so that means nothing. If your soil has low levels of Calcium and high levels of Magnesium then you need Calcitic lime, but if the reverse is true, lots of Calcium but little Magnesium, you need dolomitic lime. This is not something to guess about and your local office of your state USDA Cooperative Extension Service can help.

    Bookmark   February 20, 2009 at 7:27AM
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I finally had a chance to ask my father what kind of lime it was and I got the answer I expected, which is that he doesn't know. He believes that all lime is basically the same stuff, from the lime mixed to make cement to that contained in gravel to that contained in whole limestones, with the only difference being in the size and degree of impurities. What he has is one load of $400/dump truck lime. Next week he's going to get one load of $200/dump truck of "screenings". I'm not sure what screenings are. I think they're the small rocks that fall through the screens at the gravel quarry, but that's just a guess. He thinks this will help his garden. I have no idea.

    Bookmark   February 20, 2009 at 9:12PM
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Your father is correct for the gravel industry standards. All agriculture lime is ground limestone rock. Limestone beds reach from the rockies eastward. They were caused by various oceans where small animal life precipitated on the bottom of the oceans. Some are inches thick some are a mile or so thick interbedded with other material.

The screenings depending on the company either the small pieces dropping from the screen or for one company screenings are the pieces remaining in the screen.

Once again it depends on where in Oklahoma you are. Eastern part has large amounts of granites and schist dust in the soil. Most of these are naturally acid. The red dirt area is a mixure of an old river bed, iron, and bauxite. This could also be acidic depending on the mix. Toward the western part the land tends to be more alkline. Your acidity could be a natural condition of your soil or it could be that the soild was trucked in from a battery factory.

Have a soil test with the associated mineral complexes to see how you stand then adjust your soil. Many just automaticly add lime every year in farming. The agriculture limestone takes a long time to breakdown.

Kansas has books available showing cross cuts of the various stone beds accross the state if Oklahoma has one at the tourist centers you can use it to check out the possibilities of which limestone bed/beds your rock came from.

I would look through my geology books but many of the beds have been subdivided since I got my degree in 73.

    Bookmark   February 20, 2009 at 11:24PM
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I suspect the screenings he's getting are from the quarry east and northeast of Tulsa. The stuff he paid $400 for is a dark grey. If that helps?

The acidity of my soil is due to it being fill dirt. This is a new addition and they leveled my house site by taking dirt from a nearby hill and spreading it over the existing topsoil. Then they put sod on top of some of it. Wherever they didn't sod, even the weeds are struggling to grow in it. I don't know the pH of the native clay loam topsoil (grass grows fine in it), but the fill dirt is really nasty stuff.

Since my raised bed is entirely imported materials, I think I'll leave off the lime and just hope for the best. I know a soil test is only $30 (and I had one done last spring), but I've been laid off and every dollar is being watched. It's why I've been so up about scavenging free stuff and using what I already have laying around.

What I have in the bed now is a layer of sandy loam topsoil, a layer of oak leaves, a layer of horse manure and bedding, a layer of leaf compost, another layer of sandy loam topsoil, a layer of spaghnum moss and a third layer of sandy loam topsoil. Yesterday I soaked it down twice. I haven't seen if it's compressed.

I was thinking I'd add a layer of native topsoil to it. It has a fairly high clay content and will help with moisture retention. I've read recently that too much organic material is bad for plant growth, so I was thinking I'd top it off with 1/3 sandy loam, 1/3 clay loam top soil and 1/3 leaf compost. Maybe mix a little rotted straw in there if I can get it.

    Bookmark   February 21, 2009 at 12:30PM
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If they just leveled the hillside next to you your soil should not be much different from what it could have been if your house was on the side of the hill.

One of the things by going ahead and using the lime is that when you till it under it will help add texture to the soil.

See where the author of the book that mentions too much organic material if from. I think you will find the author is from an area that has bogs or is heavy with peat such as Michigan, Florida. When you read books try to find one thay has similar growing conditions that your area is in. As I read in another post someone writing about how to garden in PNW conditions would not know how to garden in Texas.

If nothing else use the limestone and the tailing as pathways arround your beds. That should help keep some of the compaction down.

    Bookmark   February 22, 2009 at 12:45AM
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Soil pH, whether acidic or alkaline, is the result of a chemical imbalance, not the type of soil it is. Free radical Hydrogen ions cause soils to be acidic while calcium can cause an Oxygen ion to attach to that H resulting in an OH ion that enough of will change the soil to one that is alkaline.

    Bookmark   February 22, 2009 at 7:57AM
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Calcium causes oxygen to attach to hydrogen?!? I would love to see the mechanism on that reaction, if you don't mind.

    Bookmark   February 22, 2009 at 10:38AM
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Soil pH, whether acidic or alkaline, is the result of a chemical imbalance, not the type of soil it is.

If you do the research, soil pH is directly related to its mineral content and the amount of rainfall that area receives. Soils with a high limestone content will tends towards alkalinity; those with a granite base will be more acidic and various other minerals will influence pH as well depending on their composition. Areas with high rainfall will also tend to produce acidic soils while those areas that are more arid with lower rainfall - less than 20 inches per year - tend to be alkaline. It has nothing to do with a chemical imbalance - it is what it is depending on location and soil composition and the chemicals result from whatever minerals are providing them. Rather than an 'imbalance' it is the natural state of the chemicals and how they react with each other depending on the soil type.

Most soils will have a buffering capacity that resists pH change in varying degrees. Clay soils and those that are high in organic matter have a greater buffering capacity and resist any significant changes in pH. Very sandy soils have much less buffering capacity. It is very difficult to change an acidic soil - generally those with a high clay content - to an alkaline state.

Since organic matter tends towards a more acidic pH and also increases the buffering capacity of the mix, I'd lean towards reducing that portion of the mix. Generally for inground planting conditions, an organic content of no more than 5-10% is more than adequate. Raised bed conditions would dictate something quite similar.

    Bookmark   February 22, 2009 at 11:28AM
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I live in a sandy part of Florida and we get a fair bit of rainfall. My soil tends to be on the slightly acid side, (around 6, 5.8-6.2)

However, I've done very well growing many types of garden veggies in almost 100% organic material raised beds (just mounds no sides.) It will all depend on your situation, the plants you wish to grow, etc.

The comment about where the garden book author comes from is very apt. I've seen lots of blanket statements by "master" gardeners that really should not be quite so blanket. Should you square foot garden or space things out? Really depends on the situation. If you soil is really so terrible but you can manage to make a really good intensive bed and tend/irrigate/fertilize enough, the square foot gardening may be better. Should you use overhead sprinklers or drip irrigation? Again, depends on situation. I can't legally use sprinklers more than twice a week here and with the sandy soil and extreme spring/summer heat, plants would not survive without the drip irrigation I can run as much as I need. And so on with some many things.

I suspect a small amount of lime in your raised beds could be a good thing but without knowing what you intend to grow in them, how you will irrigate them (my well water comes from a limestone aquifer,) what sort of fertilizers you will be using and many more things, it is really hard to give a solid answer.

You may just have to experiment a bit on your own. Good Luck!!!!

Here is a link that might be useful: TCLynx

    Bookmark   February 22, 2009 at 12:23PM
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