Soil vs peat

Jane McGary
Mon, 06 Mar 2006 13:05:26 PST
Dell SHerk wrote,           I read recipes for potting mixtures all over 
the horticultural
>literature. In some sources, I read about "soilless mixtures" and in other
>places I read about using peat in mixtures instead of soil - that soil is
>"bad" or that peat is "bad." I learned in my soil science class that soil
>has a mineral component and an organic component. Also, I learned that
>organic matter is broken down by chemical and biological agents till it
>reaches the particle size of silt when it no longer fills the role of
>organic matter in the soil- that is, "buffering" soil nutrient content and
>moisture.  In the long run, then, peat becomes silt and is essentially no
>longer "organic." With geophytes that we grow in the same pot for years,
>what are the implications?

I think many publications that warn against using peat are from Britain, 
where the overexploitation of local peat deposits is a serious 
environmental concern. In North America, most of our peat comes from the 
vast deposits in Canada, and we need not feel guilty using it in potting 
soil. However, I don't think peat is a good component of potting soil for 
bulbs except perhaps those that are kept constantly very moist; it's too 
hard to remoisten once it dries out. It breaks down and compacts rather 
soon. Also, a geologist friend warned me that combining peat with pumice 
would cause the pumice to break down faster. I use peat only in seed 
starting mix.

Warnings against using "soil" may reflect an awareness that garden soils 
vary greatly from place to place, and some may be composed of too many 
fines to be healthy for potted bulbs. Or it may reflect the belief that 
potting soil should be "sterile," which I think is nonsense; as soon as the 
"sterilized" components get into the pot and out in the air, they will be 
quickly colonized by microorganisms, unless they're in a totally controlled 
laboratory setting. I grow almost all my bulbs in a mixture of coarse sharp 
sand, ground pumice, and sieved but otherwise untreated topsoil from the 
woodland on my property.

I was however puzzled by Dell's reference to "geophytes that we grow in the 
same pot for years." I wouldn't leave any bulb for years without repotting 
it. All of mine are repotted every second year in freshly prepared soil. I 
use the old potting soil to amend areas of the garden. Perhaps, however, 
there are tropical bulbs that need to be left undisturbed?

Jane McGary
Northwestern Oregon, USA

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