"SunShine on plastic" is an important consideration that I forgot to address in my previous message. Sunshine from WEST direction, in the late afternoon, namely when the sun is shining horizontally, particularly in an appartment on a high floor, directly onto the side of plastic containers, on the balcony or on the windowsill, can become fatal. Surprisingly effective protection is achieved through wrapping the pots with aluminium foil ("tin foil"), at least covering the exposed side, OR cover the lowermost 15 to 20 cm of the window-glass with a sheet of tin foil.
> Date: Tue, 4 Oct 2011 15:15:36 -0700
> From: leo@possi.org
> To: pbs@lists.ibiblio.org
> Subject: Re: [pbs] Clay vs plastic
>
> This question is so dependent on one's growing conditions that there can't
> be hard and fast rules.
>
> Here in Phoenix, Arizona, with low humidty, high temperatures, and water
> with high pH and high amounts of dissolved minerals, clay does not work
> well at all. Even large pots dry out too rapidly for me to keep up with.
>
> And, the salt from the water accumulates everywhere, damaging the roots
> where they touch it. Because of salt accumulation, pot rims and edges of
> drain holes start dissolving in 2-3 years and within 5 years most clay
> pots disintegrate and fall apart. When I get a plant in a clay pot I repot
> it at once, and use the clay pot for a plant I'm going to give away to
> somebody else.
>
> I have to be quite careful of sunshine on plastic. It certainly heats up
> and can damage roots, even in winter, but I do much better with plastic
> containers than with clay.
>
> I suppose in a high-humidity, acid-water region clay would be just fine.
> And it works wonderfully for damp soil plunging.
>
> I think Berkeley has fairly salty water and low humidity despite being on
> San Francisco Bay, so I would expect plastic to perform better for Paul's
> cactus and succulents.
>
> Leo Martin
> Phoenix Arizona USA
>