gethyllis cold tolerance (Rick Buell)
Tim Eck (Fri, 23 Jan 2015 08:19:44 PST)

It's interesting and somewhat counterintuitive that this boundary effect is
nowhere near as strong and the drainage much better if you put the coarse
material on top of the fine material - probably similar to the 'brazil nut
effect'.
$.02
Tim

-----Original Message-----
From: pbs [mailto:pbs-bounces@lists.ibiblio.org] On Behalf Of Tim Eck
Sent: Friday, January 23, 2015 9:37 AM
To: 'Pacific Bulb Society'
Subject: Re: [pbs] gethyllis cold tolerance (Rick Buell)

One way to envision this boundary effect:
If you have identically sized spheres their closest packing is about 74%,
leaving about 26% voids. If you then place much smaller spheres in contact
(think gravel and sand), the sand will infiltrate the gravel voids, taking
up 74% of this 26% =19%. So, now the contact zone is 93% solid and 7% void.

Tim

-----Original Message-----
From: pbs [mailto:pbs-bounces@lists.ibiblio.org] On Behalf Of Alberto
Sent: Friday, January 23, 2015 8:51 AM
To: Pacific Bulb Society
Subject: Re: [pbs] gethyllis cold tolerance (Rick Buell)

Putting ingredients of a potting mix in layers slow down drainage instead
of improving it. This has been researched for long. Water will percolate by
gravity through a layer but when reaching the next it will collect making
the mix stay wet for longer than planned through capillarity. This s the
reason why the best potting mixes are a combination of not water retaining
materials, so excess water is rapidly forced out.