A few months ago, my neighbor Trish and I were working on her perennial garden. We were making up a material list and I said we would need a few bales of peat to till in.

Trish asked if I meant peat moss or peat humus, and what the difference was. Now there's a topic for you, she added, so I took her up on it. Today we are going to sort through some of the more commonly used soil amendments.

Let's start with the peat moss vs. peat humus question. To explain the difference, we need to look at how peat is formed. Peat is basically composed of decaying sphagnum moss with some sedges and grasses mixed in.

There are more than 300 species of sphagnum moss worldwide. They are small, primitive plants reaching a height of about one foot. They thrive in poorly drained areas called bogs or peatlands.

When the plant dies, it is pushed below the bog's surface by the weight of the remaining, living plants. Because of the waterlogged nature of a bog, normal decomposition is slowed way down. After hundreds, even thousands of years, the decayed sphagnum moss becomes peat.

Layers form as a result of the various degrees of decomposition and each layer provides us with a different organic product. The living layer of the bog (sphagnum moss) is sold as hanging basket/window box liners, a potting medium for orchids and for floral design work. It's very coarse and stringy.

The next layer is what we know as peat moss. It is sold in those fun-to-hoist, compacted bales. Its main purpose is to increase the soil's moisture retention capabilities by improving soil porosity; more pores equal more space for water to fill. It is often tilled directly into new garden soil or added as part of the back fill when planting shrubs and trees. But you must mix it in or it will retain water on the soil surface, forcing the roots to grow up in search of moisture instead of down. It has a pH value around 3.5, so with continual use, test your pH annually, and adjust it if necessary.

Reed/sedge peat is the middle layer. It is a cheaper grade of peat due to its makeup and not used extensively. The bottom layer is where peat humus comes from. It is completely decomposed, very dark in color, contains silt from the bog's floor and is often used in place of bagged topsoil by gardeners.

Some peat facts:

There are more than 1 billion peatland acres worldwide, 274 million acres in Canada, 124 million in the United States.

New peat accumulates at a rate of 50 million metric tons per year and is harvested by dredging or block cutting at a rate of about 800,000 metric tons/year.

The United States imports 99 percent of its annual peat moss usage from Canada, and harvests mainly reed/sedge and sphagnum moss.

On to vermiculite and perlite.

Vermiculite is formed from mica. When heated in furnaces, the water trapped between the mineral's layers converts to steam, popping the layers apart and forming the small gray, spongy, lightweight particles in your houseplant potting mix.

Like peat moss, vermiculite aids in water retention. It is excellent for covering bulbs stored indoors for winter to eliminate mildew and rot. Vermiculate with peat moss is a premier seed starting mix.

Perlite comes from volcanic lava flows. The mined ore is crushed, screened and heated. Its moisture also changes to steam and -- pop -- those little, white round balls you find in that same soil mix are formed. Perlite increases soil aeration and is used in hydroponic growing mediums.

Now let's jump on the ``honey wagon'' -- fresh vs. composted manure.

Fresh manure that's been piled, repeatedly turned over, ground up and dried becomes composted.

Composted manure makes awesome mulch, it is easy to spread, and moisture leaches nutrients to the roots below. Many area farms have begun composting and selling manure in bulk, which is a cost-effective way to buy.

Both manures increase organic matter in your soil and provide a source of slow-release fertilizer. One drawback: Fresh manure can burn a plant, so it is best tilled into the garden in the fall. Check your pH and adjust if needed.