Potting Mix and Drainage
totototo@telus.net (Wed, 21 Feb 2007 09:35:35 PST)
On 21 Feb 07, at 14:36, carlobal@netzero.net wrote:
AND that's not all...
The more insidious problem is the classic "perched water table". The
water that remains in the pot will "hang" disproportionately at the
interface between the potting soil and the coarse drainage material
resulting in a nearly saturated layer. Especially in the case of
bulbs, this can be dangerous.
Filling the pot with potting soil results in a more evenly distributed
water load...
And wringing the pots onto a layer of sand or similar material will
allow excess water to wick away even more. This is one of the
advantages of plunge beds: it prevents not only desiccation but also
overwatering.
There must be capillary contact between the soil mass in the pot and
the sand it sits in/on for this to work.
I sometimes put up a few hanging baskets of fuchsias for the summer;
these baskets are close to hemispherical and I have my doubts about
the efficiency of their drainage. And hanging in mid-air as they are,
of course there's no way to provide capillary drainage.
When I've really had a bee in my bonnet on about my fuchsias and
their water supply, I've gone so far as to insert 2' or 3' lengths of
coarse garden twine into the drain holes. Long after watering a
basket, there's still a slow steady drip drip drip from the ends of
these as good old capillary action gradually removes the excess from
the soil mass above.
It looks pretty silly and I suppose it *is* pretty silly, but it
remains a good lesson on the merits of capillarity. Wasnt't there a
famous case of theft from a winery in Italy years ago where a huge
wine vat was emptied by thieves using lengths of rope to drain it up
and over its edge?
--
Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate
on beautiful Vancouver Island