I second Wayne's hands-on experience. I have rock-hard alkaline clay, pH 7.7, high in magnesium. The soil is so hard that it broke my large rototiller machine, and a shovel. My husband used a pick-ax to dig holes. 12 years ago I planted 6 rhodo. and azaleas. I brought down my pH by mixing 1/2 peatmoss. I never water those acid-loving plants, they are still alive. This year I used acid-fertilizer FOR THE FIRST TIME to increase the blooms and foliage - they have tons of buds now. I have a large rose garden with 42+ roses. Since roses are fussy, I move them around or dig them up to gargage them in my zone 5a winter. I made many holes: 1) pine mulch mixed with clay gave the fluffiest soil and best root-growth, thus most blooms. Pine bark is dry at first, but once decomposed, it retains water. A rosarian faxed me the ARS paper on field experiment on a large scale that documented dryness of pine bark at first, but once decomposed, it retains water. That's why the large Ball professional potting soil has 45% COMPOSTED fine pine mulch. Another hole with 1/3 peat moss, 1/3 pine park, 1/3 native clay .... Six months later I dug the rose up: the soil is fluffy, but rooth growth is less. Another hole with 1/3 coarse sand, 1/3 pine park, 1/3 clay, then topped with alfalfa meal. Six months later I dug up, and found tons of earthworms. Several holes with 1/2 peat moss and 1/2 clay. I dug the rose up: Root growth is restrained, soil is still compact. Another hole with 1/3 grass clipping, 1/4 peatmoss, 1/4 alfalfa meal, and native clay. This glued up badly, soil became more compact. The grass clipping is innocent, the culprit is the fine particles of peatmoss and alfalfa meal which binded with the high positive charge of magnesium in my clay soil. Alfalfa meal is high in calcium, and calcium precipitates in alkaline clay, making phosphorus unavailable for blooms. Why I do such experiments? I majored in chemistry for 2 years before getting my B.S. in Computer Science. It's fun to use my chemistry background to experiment in the garden. I second everything Wayne wrote. He's right, experience and ACTUAL TESTING over many months is the best teacher.

I also have found coco coir to be excellent for seed germination. Coir is going to be superior peat for this for the same reason a paper towel is. It actually allows the seed to stay consistently moist. Peat dries out faster and doesn't have a reliable pH. You also don't have to worry about a bunch of sticks with coco. No nutes necessary for germination. The seed has its own food. Problem is, you have to transplant pretty soon or use liquid fertilizer if you use a medium without nutrients. I make soil blocks with a coco coir/vermicast/sifted compost mix so I don't have to worry about a quick transplant. Coco also won't mold or grow moss and algae on it like peat moss does. At least not until you put nutrients on it. It's just you adding the nutes instead of a pump. There is a very good reason peat isn't used for hydroponics but coco is. Coco is more stable, nearly all brands desalinate as they know the hydro industry is their number 1 customer - so normally no worries concerning salt, and it it's great for aeration because it doesn't break down as fast as peat moss. In fact, I sterilize, desalinate, and reuse the coco for my hydro plants. It lasts at least 3 growing cycles of tomatoes and many more for lettuce (shorter cycles is why). For anyone thinking, "But I don't do hydro," keep in mind that potted plants that require liquid fertilizer is hydro. It's just you adding the nutes instead of a pump. I hold no illusion that coco is more environmentally friendly. I did, because I fell for the media hype. But the reality is otherwise and I now definitely recognize this.

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.

Thanks for your responses. I'm all for just using what I have on hand--straw, grass clippings, shredded leaves, left-over sawdust, kitchen scraps, bagged manure, etc. instead of buying peat moss. I'm glad to hear it isn't necessary.