In case the link is ever broken, cut and paste the PDF file here: Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University The Myth of Gypsum Magic âAdding gypsum to your yard or garden will improve soil tilth and plant healthâ The Myth Upon continued prodding from one of my university extension colleagues, I recently watched several episodes of a well-known gardening program on television. My kids joined me, alerted by my animated responses to the hostâs non-stop torrent of advice. Among many amazing discoveries I learned that by adding gypsum to my yard or garden I would improve my problem soils by changing the particle size and loosening compaction. Further searching on the web revealed that gypsum would also improve drainage, decrease acidity, and eliminate soil salts. Previously, I had heard of gypsum for use in soil reclamation projects, but not for a typical urban landscape. Since gypsum is simply calcium sulfate, could this chemical truly transform soil structure and serve as a fertilizer for yards and gardens? The Reality This myth falls into the category of agricultural practices misapplied to ornamental landscapes. Gypsum effectively changes the structure and fertility of heavy clay soils, especially those that are heavily weathered or subject to intensive crop production. Gypsum also improves sodic (saline) soils by removing sodium from the soil and replacing it with calcium. Therefore, one can see improvement in clay soil structure and fertility, and desalinization of sodium-rich soils, by using gypsum. What other effects will gypsum have on soil and plant health? There are a number of scientific studies on gypsum usage both in the literature and on websites. Briefly, researchers have found: ⢠Gypsum does not usually change soil acidity, though occasional reports of both increasing and decreasing pH exist; ⢠Gypsum can increase leaching of aluminum, which can detoxify soils but also contaminates nearby watersheds; ⢠Gypsum can increase leaching of iron and manganese, leading to deficiencies of these nutrients; ⢠Gypsum applied to acid soils can induce magnesium deficiency in plants on site; ⢠Gypsum applied to sandy soils can depress phosphorus, copper and zinc transport; ⢠Gypsum can have negative effects on mycorrhizal inoculation of roots, which may account for several reports of negative effects of gypsum on tree seedling establishment and survival; ⢠Gypsum is variable in its effects on mature trees; ⢠Gypsum will not improve fertility of acid or sandy soils; ⢠Gypsum will not improve water holding capacity of sandy soils; and ⢠Gypsumâs effects are short-lived (often a matter of months) With the exception of arid and coastal regions (where soil salts are high) and the southeastern United States (where heavy clay soils are common), gypsum amendment is just not necessary in non-agricultural areas. Urban soils are generally amalgamations of subsoils, native and non-native topsoils, and - in home landscapes - high levels of organic and non-organic chemical additives. They are also heavily compacted and layered (and gypsum does not work well on layered soils). In such landscapes, it is pointless to add yet more chemicals in the form of gypsum unless you need to increase soil calcium levels. This nutrient deficiency can be quickly identified by any soil testing laboratory for less than a bag of gypsum costs. (If you need to improve sulfur nutrition, itâs wiser to use ammonium sulfate). To reduce compaction and improve aeration in nearly any landscape, application of an organic mulch is more economically and environmentally sustainable. The Bottom Line ⢠Gypsum can improve heavy clay soil structure and remove sodium from saline soils ⢠Gypsum has no effect on soil fertility, structure, or pH of any other soil type ⢠Most urban soils are not improved by additional gypsum ⢠Before adding gypsum or any chemical to a landscape, have soil analysis performed to identify mineral deficiencies, toxicities, and soil character ⢠Adding gypsum to sandy or non-sodic soils is a waste of money, natural resources, and can have negative impacts on plant, soil, and ecosystem health For more information, please visit Dr. Chalker-Scottâs web page at http://www.theinformedgardener.com.

I'd argue that the main takeaway here should not be debating whether spontaneous combustion of potting soil is possible or extremely rare or impossible (although fire marshals say it is, and it is pretty well established it exists in other circumstances/other materials, so can't be ruled out). The main takeaway is: some types of potting soil (esp peat) are extremely flammable and should not be stored in places where they would cause fire damage, even in a garage or greenhouse or shed. Whether combustion is from some unknown spark or biological or chemical reaction or other, it can burn - even if it seems almost impossible. From some experience with peat - it can be very flammable; it can smolder unnoticed for quite some time (with not much, almost no, smoke showing); heat can build up inside due to it being tightly-packed (structurally); there may be unexpected situations like it being at high temperature internally - smoldering - just waiting for enough air to flame up. It just shouldn't be stored like this, even if likelihood is low.

I do not always have access to pumice so I mix it up with whatever grit I have hanging around. Expanded shale. , washed 1/4 Decomposed granite , course red lava sand, perlite. I am not anal retentive. I am more of the "what's in the frig" kind of gardener. I do not know if you are in Florida, California or Texas. The quantities will be important to your location and how humid you are. I know Floridians who grow in 100% grit, and inland Californians who use more humous in the mix. Its a mixed bag here in Texas as U sit under the remnant of Hurricane Harvey who might be leaving 20" on me. I have also gone all summer often without summer moisture. Not this year.

No way! It's true that most of our soils are acidic, and our rocks are infamous; but there are pockets of alkaline soil, and chunks of clay, and sandy expanses with nary a rock in sight. If you're willing to take a chance with expensive (and/or beloved) acid-requiring plant material, then most of the time you'll be OK. However, it's safer to have the soil tested before you go ahead and plant. WHAT IS NEW ENGLAND ANYWAY? The classic view of New England, as learned by local schoolchildren, includes the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island and Connecticut. It rolls off the tongue like A,B,C,D,E ... The problem is that the Atlantic Ocean bounds New England to the east and Canada lies to the north, but there isn't a clear boundary to the west or south. Portions of eastern New York along the Hudson River kind of blend into Vermont, Massachusetts and Connecticut, and Long Island can be suspiciously like Cape Cod or the south coast of Massachusetts, Rhode Island and Connecticut. Open-minded New Englanders are inclined to accept New York as adjunct New England territory for some purposes, so long as the New Yorkers don't get too uppity about it. A SHOCKINGLY BRIEF AND SUPERFICIAL GEOLOGY SUMMARY A very long time ago, long before Spike started Garden Web, there were continents drifting and colliding, and volcanoes spouting lava, followed by glaciers grinding up the rocks, sliding and melting, and depositing stuff all over the land. A turbulent time. The most recent ice age, the Wisconinan, started about 80,000 years ago and finished up about 14,000 years ago. Coming here, it scraped material off mountains and bedrock and carried with it whatever rocks were too hard to grind up. The softer rock got ground into smaller and smaller particles, ending up as what we now call gravel, sand, silt and clay. When the glacial lobes started melting and retreating, these rocks and particles dropped out and either stayed put or were redistributed by the melt-water rivers. The outwash plains and deltas contain large amounts of sand and gravel. Just look at the beaches on Cape Cod and the south coast of Massachusetts, Rhode Island and Connecticut. Huge glacial lakes formed, with sediment at the bottom, and these glacial lakes were later emptied when temporary dams burst. The sediments often contain veins of clay and silt. Clay and silt deposits are found along the northeast coast and around Lake Champlain. Smaller kettle ponds were formed when a big chunk of ice melted in place and slowly seeped away until the level reached the water table. These kettle ponds soon filled with organic material and many became bogs. The temperature differential near the retreating ice sheet caused fierce winds to blow and deposit sand and silt every which way, and many upland soils in New England consequently are heavy in sand and silt. As if this wasn't enough, the land gave a sigh of relief as the weight of the ice sheet diminished, and started to rise up, shedding water in the process. However, the sea level countered by also rising, bolstered by the melted glacial water. Sea water covered various parts of New England and marine organisms lived and died, leaving their shells behind. Eventually these shells were transformed into their own idea of rock, resulting in marble, limestone and dolomite deposits in various parts of New England, notably in western Connecticut and northeastern Maine. The final affront to the New England geology was the arrival of humans. We farmed, filled in marshes, rerouted rivers, dug foundations and transported excavated material to landfills wherever we felt like it. The Big Dig in Boston is one of the latest and biggest examples of redistribution of earth by human activity. With all of this diversity in soils, it's no wonder that people always say you should have your soil tested if you want to know what you're dealing with. A FEW EXAMPLES FROM GARDEN WEB MEMBERS treeskate has problems with vernal pooling areas: "We have many small streams that overflow periodically throughout the year - and many of them are not in full sun. Planting is a real challenge! When I had 8 samples done by UCONN it was truly amazing the different levels of nutrients (Calcium, Magnesium, Phosphorous, Potassium) and various pH levels, sandy loam, and organic content. It was mind boggling!" mad gallica in New York State: "...technically a bog is a wet place with a low pH. I don't have a bog, I have a limestone fen. A lot more plants will grow there because there are a lot more nutrients available. I don't really garden down there because I'd have to keep the cattails and phragmites under control." cady on the MA north shore has some clay soils. bogey123 near the CT coast : "I lived about half a mile from the long island sound in south western fairfield county and you couldn't dig more than a few inches without hitting rocks of all sizes and shapes. Yes the soil is a bit on the acidic side too." swanz in NH: "I live in SW NH, sandy, gravelly, acidic soil in my town." swanz also has a friend who lives 25 minutes away, but has clay soil. byron lives in NH, but says there are lime mines in Lee, MA. Lee is in the far west of MA near the NY border. narchnh in southern NH: "My only comment would be to emphasize what others have already pointed out, namely, that soil conditions here are about as variable as the weather. Even on one lot the range of soil types, pH, moisture, etc. can vary widely, so in many cases multiple samples would be necessary to get a true picture. For example, I am in an unusual(fortunate?) situation in that I live on top of a small rise right on the edge of the Connecticut River flood plain (across from Wethersfield Bow, if you know the river). Under an 18-inch layer of loamy sand it is, literally, about a 50 foot deep, maybe more, hill of almost pure sand. The only rocks I have ever hit when digging my gardens were placed there by previous owners (old foundations, wells, etc.). The downside is that my soil drains in minutes and dries out quickly, and in a week I can have crispy lawn syndrome. Great drainage for perennial beds, if they are mulched, but not your typical "thin soil over granite bedrock" like I had at my last house. BUT, in some places there is a clay-based underlayer, probably pockets left over from when the river or the streams on the property meandered through thousands of years ago. These areas retain water and have a very different profile. I can easily spot them right now out on the lawn, because in those places the grass is green and tall compared to the crispy lawn around them. On top of this the land has been farmed for over 250 years, so it has been modified with years of tilling in cover growth, cow manure, etc. Depending on where you live, that could definitely play a role in soil quality, since so much farmland is being converted to housing. Again, my point would be that, unless someone really knew that their soil was homogeneous, if they were going to garden in four places on their property and wanted the soil tested, then they should take four samples. More expensive, but it would save money in the long run through fewer lost plants." SO WHAT'S IN GARDEN SOIL? The short answer is, a mixture of inorganic particles derived from rock, plus organic material, plus nutrients, plus various trace minerals. A healthy soil will also have bacteria and fungi and earthworms (although there is an anti-earthworm lobby). USDA SOIL CLASSES - PARTICLE SIZE AND SOIL TEXTURE The USDA recognizes three soil particle sizes: from biggest to smallest - sand, silt and clay. These are usually all present in soil, but in different proportions. Put these together and you have a series of 12 soil texture classes starting with sand, loamy sand, sandy loam, sandy clay loam, ... you get the picture. The important thing to remember is that the more sand, the better the drainage(water races through), the more clay, the more the water is retained. AND WHAT ABOUT pH? pH is a scale ranging from 1 (dangerously acidic) to 14 (viciously alkaline) which can be used to measure the chemical environment in the soil that the plant has to deal with. pH 7 is neutral. Soil pH within a range of pH 4 to 8 is not outrageous, but different plants will grow at acidic pH 4 than will grow at alkaline (basic) pH 8. The pH is mostly determined by the parent rock from which the soil particles were derived. Lots of limestone and the pH goes up towards alkaline. Most soils in New England are acidic, but areas with considerable limestone, dolomite or marble deposits tend to be alkaline. A soil test will give you the pH of your garden soil and tell you how to amend it if you want or need a different pH. However, don't think that you can change the pH once and forget about it. You'll probably have to re-test and re-amend every year or so. Soil has a short memory and will revert to the original pH (or close to it) if you don't keep an eye on it. Did I mention you should have your soil tested? It's easier than you think, and not very expensive. HOW TO HAVE YOUR SOIL TESTED The Cooperative Extension System is an agency within the United States Department of Agriculture (USDA) and has local offices in each of the New England States. A web search for "Cooperative Extension System" will give you local contacts. Note that soil testing is usually listed under agriculture or horticulture. When you order the test material you will be given a detailed procedure to follow. The Soils, Compost and Mulch Forum FAQ on Soil Testing and pH gives a good description of the process. WHAT DO I DO WITH THE SOIL TESTING RESULTS? The analysis will tell you what your soil contains and how to amend it to achieve certain goals. Be aware that the soil analysis recommendations may be based on bringing the soil to a generally acceptable standard, such as a more neutral pH. If you're planting something unusual that would like the odd-ball soil conditions, you may not want to follow all of the recommendations. That's the point where you might want to post a question on the New England Gardening Forum or the Soil, Compost and Mulch Forum. Lots of knowledgeable folks on both forums. A FEW USEFUL REFERENCES Print "The New England Wild Flower Society Guide to Growing and Propagation Wildflowers of the United States and Canada" by William Cullina is aimed at gardeners and is excellent on soil. "Roadside Geology of Massachusetts", by James W. Skehan is part of a series of geology books for specific states. Very detailed and easy to read. treeskate recommends The Face of Connecticut - People, Geology, and the Land" by Michael Bell. "It is divided into 'Landscapes' (central valley, uplands, the coast, 20th Century Landscape) and 'Geology' (a sense of time, Mapping the land, the changing face of Connecticut, Qui Transtulit...) Great illustrations, drawings, etc. to better understand a particular area and the type of soils found. Internet sites The Society of Soil Scientists of New England has a website with presentations on New England Soil Formation/Genesis and other good information The website of The National Resources Conservation Service (NRCS), an agency of the USDA, has excellent soil survey data.