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Soil, Compost & Mulch

How to balance acidity of peat moss?

14 years ago

I'm planning to add some peat moss to lighten my clay soil Â probably about 3 inches, forked into the top 9 inches of soil, together with some compost. How much lime should be added to counteract the acidity of the peat moss? Will the lime leach out, and have to be re-added periodically? Would wood ash work as well / better?

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Comments (5)

digdirt2
14 years ago
Compost is even more effective at improving clay soil than peat and doesn't have the acidity problem or the other associated peat problems. Can I ask why you'd rather not just use compost?

But if you prefer using the peat for some reason then IMO the only way to know how much lime or wood ash would be needed would be a soil test. Lime and especially wood ash can effect quite drastic changes though IME using dolomite lime is less drastic.

But even if you know the pH of your existing soil, there is no way to know for sure what effect the peat may have or how quickly it will affect the pH without testing.

Dave
nygardener
Original Author
14 years ago
Compost alone definitely makes my soil more fertile and easier to plant in, but it decomposes and disappears very quickly. It also seems to compact more in wet weather. I was hoping a mix of compost and peat would cause a more lasting (and stable) improvement in tilth, and a steadier volume of soil throughout the season.

Unless peat varies greatly in acidity, I'd think there'd be a rule of thumb for how to balance it. Otherwise, I guess I could throw some in a bucket, add some lime until it's neutral, and then do the math ...?
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If dolomitic limestone is added, it's my understanding it will be on the label. In my experience the sweetened stuff is not brought all the way up to 7 but is instead brought to about 5.5 which is the "ideal" pH for potting soil. Soils made almost entirely of organic matter are said to function chemically (providing a similar profile of nutrient availability) like more mineral soils do at one point higher pH. Anyway, that's what I was taught years ago at hort school. You should amend your medium with sulfur, even if you find untreated peat moss, as peat breaks down very quickly and thereby looses much of its acidifying affect after a few short years.
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Peat is water retentive, but not as much as clay soil. If your beds are currently sandy peat would help, but if they are clayish probably not going to help much with water retention. Another consideration with peat is that it is hydrophobic when dry. You can water the bed and think it must be soaked, but really the water is running off. This isn't a huge problem if you use a mulch and irrigation hoses under it, but otherwise it can be a bit of a pain in the summer. Having said that, it can be a nice soil amendment for keeping the soil loose. Compost is much the same, but tends to not last as long as peat does which can be good or bad depending on one's perspective.
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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.
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Both Kimmsr and Wayne have valid points. My best result in breaking up clay was when we rototille fresh grass into the soil early spring, with a bumper crop of tomatoe. My second best result was when we used A HUGE PILE OF COARSE SAND. Someone mentioned using fine pine mulch to break up clay. Great idea! Walmart sells them for $2.88 per bag. We rototilled them into the soil, it was nice and fluffy. For the same result would take 10 times the amount of sand. I looked at the ingredients on the professional potting soil made by Ball Corp. for their annual flowers: 40 to 50% composted FINE pine parks, peat moss, vermiculite, perlite, lime, and gypsum. This soil mixture yields better result for my roses than green-bag MiracleGro potting soil, and Organic MiracleGro potting soil (brown bag). The 40% Composted pine mulch potting soil is much lighter, fluffier, holds water longer, and I don't have to water pots everyday in hot summer.
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joepyeweed
14 years ago
I'd skip the peat and just use compost... lots of it.

Amending your soil is never a once and done kind of thing. Its something you should do continuously...
Kimmsr
14 years ago
Peat moss is touted as something to acidify a soil but if adding Oak leaves and pine needles do not significanlty change a soils pH why would peat moss? As Dave and Joe have already suggested compost would be a better material to add to any soil, clay or sand, since it will have active soil microbes in it which peat moss lacks. Kip on Victory Garden has stated he likes to use peat moss to amend soils because it last so long and it does because the soil bacteria, that are making nutrients available to your plants, will not digest peat moss because it is nutrient free. So in addition to the peat moss you need to add something that has nutrients in it anyway to feed the plants you are trying to grow.
robertz6
14 years ago
Rather hard to answer unless information on the pH of your soil, and the pH of the peat moss (are there two types, I think I recall?) are provided. And the type of plants that will be put in or grown, you may not want a 7.0 soil pH.

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