watering the sand between pots in a plunge bed

Karl Church 64kkmjr@gmail.com
Fri, 01 Mar 2013 12:36:18 PST
Roger, your zone is milder than mine (9a-b) here in Dinuba, CA. so I'm
wondering what you would suggest I use since I plan to build a plunge bed
later this year.
Karl Church
On Mar 1, 2013 12:20 PM, "Rodger Whitlock" <totototo@telus.net> wrote:

> On 28 Feb 2013, at 18:05, Gastil Gastil-Buhl wrote:
> > Hi PBS folks with plunge beds,
> >
> > Should I only water the pots or should I also water the sand between the
> > pots in a plunge bed?
> When I had plunge beds, I just turned the hose on them, using a good rose,
> so
> everything got watered, bed, pots, everything. [Nelson appears to no longer
> make the watering roses I prefer. They have a baffle in them to break the
> force
> of the spray.]
> > The between-pots sand is as coarse as sand gets before it gets called
> > gravel.
> That may be a mistake. As far as moisture management is concerned, plunge
> beds
> operate via capillary attraction, and fine sand has a greater moisture
> holding
> capacity. It's also important that the sand be in direct contact with the
> soil.
> Thus if a pot is overwatered, the excess is wicked away (via capillarity)
> into
> the sand bed and thence into the surrounding soil. If a pot begins to dry
> out,
> the sand and surrounding soil act as a source of moisture. The overall
> effect
> of a plunge bed is to greatly even out conditions in the pots, which would
> otherwise vary between flooded and desiccated.
> When I had plunge bed, I always used red terra cotta pots in them with no
> drainage material in the bottom, again in order to maintain that
> all-important
> capillary contact between potting compost, sand bed, and surrounding soil.
> Note that if you don't have plunge beds, terra cotta may be
> counter-productive.
> I remember Alberto at the 1993 Western Study Weekend in San Mateo,
> California,
> remarking that he grew his bulbs in (unplunged) plastic pots; terra cotta
> would
> have been subject to evaporative cooling, which would have kept the soil
> too
> cool for the bulbs he was growing. (Alberto may have since changed his
> practices, and I hope he will speak up if my account misrepresents his
> point of
> view.)
> --
> Rodger Whitlock
> Victoria, British Columbia, Canada
> Z. 7-8, cool Mediterranean climate
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