Call Now! Potting soil or potting mix is the basis for healthy plants, from indoor houseplants, to container gardens and raised vegetable beds. You can create a mix primarily for starting seedlings, for specific plant types like cacti, or for potted trees and shrubs. Sphagnum Peat Moss — Used for its excellent drainage and aeration abilities, sphagnum peat moss SPM also bulks up potting mixes without adding a lot of weight.
It breaks down very slowly and, once wet, helps retain moisture fairly well. For all of its attributes, SPM has very few nutrients and has an acidic pH 3. Adding limestone to the SPM helps to balance out the pH. We grow blueberries in a buried bale of peat moss, as recommended by local fruit growers, with great yields. Blueberries in native soil without amendments rarely survive for more than one growing season here.
Some people have been able to get good yields for 10 years or more with one bale, so it can last a long time. In this case we use normal irrigation water but do use fertilizers that are recommended for acid loving plants, so that might help maintain acidity or whatever it is that peat moss provides.
I also mulch them with conifer needles old Christmas tree boughs over the winter, which might help too. A better experiment would be to grow blueberries in a variety of soil amendments and see what works best.
I found several experiments like this for restoration studies, but again they were not able to explain why peat usually works so well compared to other amendments. A good test of comparative soils chemistry with such an experiment might be illuminating. Thank you for the article and experiment. So many articles and YouTube videos recommend Peat Moss to acidifying soil. Nice to see a science based answer. You make good sense Robert and I suspect the main advantage of the peat is physical rather than chemical.
I would expect raised beds of peat where they might receive less alkaline drainage water to retain their acidity longer. Some of our Somerset peats are of alkaline nature. Great article.
We use to use peat moss 20 years ago as was recommended by nurseries. Since then we have used Agricultural Sulphur with good results on our acid loving plants azaeleas etc. My questions is,is Agricultural Sulphur the correct Sulphur to use? Or is all sulphurs the same? Geologically young, high CEC soil is probably why. Rhizosphere pH is probably much lower than bulk soil pH. Rhizosphere pH can be quite different. Yes, you are right, the rhizosphere pH can be quite different in Wellington county Guelph, Cambridge, Kitchener, Elora.
As a matter of fact, the latest agriculture Canada report states that the A horizon fluctuates between 6. So basically, the rhizosphere pH ranges from 6. Last time I was there, those plants were performing very well. There are two groups — one bunch is almost dead. While all organic material will go through an acidic phase while decomposing, it does not mean that they are long-term contributors to overall soil acidity. I do not know of any reputable garden centre or website that advertises long term pH acidity gains from peat moss use.
It may be dated information, but the Dallas Chapter of the Azalea Society recommended a blend of half moistened peat and half finely shredded pine bark mulch for the raised beds that contain their acid loving plants.
This seemed to do the trick for the Dallas Arboretum which designed their beds on their advice and has thousands of Azaleas in an area of alkaline soil. This advice is what I used to grow my azaleas as well. They have lovely green leaf color and our water is supposedly from an area west of town that is alkaline.
Thanks, Robert for giving us more details on why this works. Baking soda has a ph of only 8. Notice the bubbles that form when you mix baking soda with acid? Those bubbles are carrying away oxygen, thereby increasing the ratio of hydrogen. More hydrogen means higher Potential Hydrogen PH.
Press here to subscribe. Garden Myths - Learn the truth about gardening. Does Peat Moss Acidify Soil? By on Some very desirable plants like rhododendrons, azaleas and blueberries demand acidic soil and many gardeners have alkaline soil which is not suitable to grow these plants. Does peat moss change soil pH?
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A peat with a pH of 4. Let me explain with an analogy of a hotel versus a small motel. Until you know the total capacity of each lodging, knowing there are 25 rooms occupied in each lodging gives you little information about how many rooms are still vacant. The pH value of each peat is comparable. Even when bases like calcium and magnesium are extracted, a peat sample can yield a greater quantity of bases equal to a greater number of guests and still have a lower pH equal to a lower percent occupancy.
To predict the lime requirement of a peat, one must determine the total capacity for base saturation, and the percent of that capacity already saturated with bases. The total capacity of a peat to hold bases is based on its cation exchange capacity, where cations positively charged ions like hydrogen, calcium, magnesium are swapped for one another.
A high cation exchange capacity generally imparts a high buffer capacity. During growing, a peat with high buffer capacity will have great ability to trade other cations for hydrogen ions that are coming from plants, fertilizers, microbial action, etc. Thus, that kind of peat resists pH drifts, which is a property we desire in a mix. Sphagnum fuscum seems to be a species with high buffer capacity. Finally, we generally think hydrogen is the source of acidity in peat.
But interestingly, iron is found in Alberta peat. Iron bonds with hydroxide in water leaving acidic hydrogen ions in the solution.
Variations in peat pH could be due to differing amounts of iron as well. But the value and the headaches it brings are well known. Most lime companies primarily serve the construction market and to them agricultural lime is a byproduct.
The burden is on us to decide whether their lime serves our purpose or not. Lime has to dissolve to act and neutralize peat acidity. We generally agree that the size of a lime particle affects its solubility: smaller particles dissolve faster.
Unfortunately, this is yet another time of getting into trouble when agriculture perceptions are transferred to horticulture. In agronomy, they have time. A slow rise in soil pH in months and a residual lime effect that lasts for 3 years is okay in field crops. In greenhouse growing, we want rapid rise— in days if not hours— and the residual effect for just months. This result makes one suspect that particle size alone may not characterize horticultural lime sufficiently.
Nine lime samples from our production plants figure 5 and 40 from Martin Marietta quarries were gathered. Among these limes, there were dolomites comprise calcium and magnesium carbonates and calcites comprise just calcium carbonate. These samples were tested. When these limes were tested to find out how fast they react and neutralize acid, there were tremendous variations in dolomites coming from different sources.
But there was very little or no variation between calcitic limes indicating it is difficult to change dolomite sources and easier to change calcite sources. Smaller lime particles did react faster than larger particles, but the tremendous variations in reaction rates were not fully related to particle size alone. Particle size accounted for only half of the reaction rate of lime.
This finding gives an explanation of how mix pH can vary despite using limes having the same sieve analysis, if these limes are coming from different sources.
Same sized lime particles taken from different sources were reacted. Dolomites took longer time to react than calcites— four times longer on average. So, is reaction slower because of the presence of magnesium carbonate in dolomite? What other character of lime is influencing its neutralization capacity? Surface area of lime particles was measured. Same size lime particles from different sources had different surface areas— up to a 5-fold difference.
This indicates that the exposed area on some lime particles is not just on the geometric surface and that there is considerable internal surface. When viewed using a microscope figure 6 , lime particles that have low surface area appear smooth.
But same sized particles from different sources that have high surface area have many ridges and valleys, which increase surface area.
Since all the exposed area reacts with water, the same-sized lime particles from different sources can react differently. These findings tell us that in addition to the sieve analysis, and of course reaction rate, content and surface area should be included in the specs to further reduce the variability of lime. The goal of the research is to find out which characters determine neutralization capacity of lime and which characters determine neutralization requirement of peat and then match them suitably.
Like what the eHarmony guy says about profiling different dimensions of men and women before matching soul mates! Continuing with the matchmaking analogy, you might be wondering: What about the chemistry after marriage— pH drift during growing?
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