In article , "David E. Ross"
wrote:

On 8/27/2008 6:54 PM, Ed wrote:
We have a lot of planters, containers, and large pots full of annuals.
Would
like to re-use the potting mix. Any input would be most appreciated.

Several things can go wrong with reusing potting mix. Nutrients are
depleated by the plants that were growing in it. Its organic components
are further decomposed, changing the nature of the mix. Salts can build
up from both tap water and fertilizers.

When I repot a plant, I might reuse half of the old potting mix and add
fresh mix for the other half. (See my recipe for do-it-yourself potting
mix at http://www.rossde.com/garden/garden_potting_mix.html.)

As mentioned earlier in this thread, the half of the old mix that I
don't reuse I put in my garden. It still has more organic matter than
my adobe clay soil, and any salts will leach away.

"Reusing" pot mix should probably be restricted to recycling it into the
main gardens. The reason NOT to do so would be because it was a badly
chosen & never a good product to start with. It's unfortunately very
common for potting soil products to mix in with lots of non-soil
ingredients, like polymer pellets or other alleged super-absorbant toxic
trash that is frankly a scam on gardeners. They usually appear as white
speckles in packaged soil mixes and should be strictly avoided in favor of
true organic potting soils.

Polymers are the equivalent of mixing styrofoam packing peanuts into the
garden, & Frank Shields of the Soil Control Lab in Watsonville California
has shown polymer products actually retard moisture retentention and can
kill some plants (killed cucumbers in test samples). "Super absorbants"
sold with the promise of cutting down the need to water much are one of
the half dozen worst tricks played on gardners by scam artists posing as
garden supply companies, whose real goal is to take something that would
otherwise cost a lot to dispose of as toxic waste (like polymers or
rubber) & sell them to easily conned gardeners for an enormous profit.

But the issue of nutrient depletion in a pot full of dirt is a red herring
if "reuse" is in the garden rather than the next pot. Even sand or peat
mixed into soil can be profitable to gardens, nutritionally inert
ingredients being important to overall soil health. And the small amount
from a planter scattered about is at worst innocuous.

One exception I would make to reusing soil mediums one pot to the next pot
is some of the stuff used for epiphytes -- orchids or orchid cacti. Some
"large chunk" mixes of rock-bark-etc are void of nutrients to start with
and as good second time around as first time, and can even be
steam-sterilized without injury to its worth.

-paghat the ratgirl
--
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