Most gardeners are familiar with sphagnum moss and peat moss, but many likely do not know the differences between these soil additives.

Both are used to help soil stay moist and to prevent soil from getting hard-packed. Both start out as the same living plant: sphagnum moss. The one sold and used as sphagnum is harvested live and then dried. It is either left whole, long and stringy, for basket liner for plant pots or it is chopped for mixing with soil.

Peat moss, on the other hand, begins as sphagnum that died naturally, became covered by a new layer of living sphagnum with other plant species joining in over hundreds of years. Eventually all the plant matter died and, along with insects and twigs, slowly melted into a water-soaked bog. Thus garden sphagnum moss is pure sphagnum and not so old.

Peat is a mix of sphagnum and other organic stuff that has aged for up to several thousands of years in water. Sometimes it is marketed as “sphagnum peat” which might make it confusing, but it is true.

The cells within both live and dead sphagnum plants can hold a lot of water, up to 25 times the plants’ own dry weight. That water retention ability is why moss is valuable for improving soil. It is not a fertilizer, though. It is the physical traits of soil that sphagnum helps.

Pure sphagnum moss is near neutral, neither an acidifier nor pH raiser. The finely chopped version is used commercially in seed starter mixes. It is often an ingredient in potting soil mixes available in bags from a couple of pounds on up. Since there is less living sphagnum around than the dead peat, pure sphagnum costs more.

Peat moss is used similarly in potting mixes, but it is also used in larger-than-pots gardening. Peat is very acidic and is a favorite addition to the root zone soil of blueberry bushes, azaleas and other acid lovers. Peat is still not a fertilizer, but it does affect the uptake of fertilizer by acidifying soil.

Natural growths of sphagnum and subsequent peat are found in many areas of the world. About two thirds of the world’s supply is in Russia and one fourth is in Canada. New Zealand, Chile and Argentina are southern hemisphere countries where harvest is ongoing.

Several European countries have reduced or stopped harvest because of concern about natural replacement of harvested bogs.

In the United States, a little sphagnum is harvested in Michigan, but most used here comes from Canada, where harvest is monitored and regulated so as to not deplete the growth and accumulation. Nearly all is harvested as peat.

Currently, the Canadian government estimates annual harvest to be one million tons per year and natural creation at seventy million tons annually.

What I find interesting is the harvest equipment.

A peat bog is drained and dried and then a giant vacuum cleaner moves in to collect the peat to be baled and marketed.

Terry Rector is a community columnist for The Vicksburg Post.