As I said on here once before, I do not know a lot about small particle physics. By observation, as well as my understanding however, clay does retain more moisture, and for longer, than sand does, when wet and in a drying environment. It is that ability to absorb more moisture than sand which allows clay to prevent light rain, during a dryish summer from waterlogging deeper soil. The surface clay will both retain water and seal the surface -forcing excess excess to run off. The more open nature of sand allows moisture both to be evaporated and absorbed much more quickley than with clay. Peter (UK) On 14 May 2015 at 21:43, penstemon <penstemon@q.com> wrote: > > >I think that the > seasonal nature of moisture is what makes these bulbs adapted to heavy > soils. Some of them grow very deep where there may be just enough > residual moisture and coolness to keep them from desiccating. > Water is withdrawn from the soil profile at a faster rate in clay soil > than in sand (by evaporation), so I imagine the bulbs are pretty dry in > summer. I wonder if it’s the relative absence of air in clay that keeps the > bulbs from desiccating, rather than residual moisture. > So, for example, I can provide the “dry summer rest” needed for some bulbs > simply by growing them in heavy soil, because it never rains enough in the > summer here for water to penetrate very deeply. > If I grew the same bulbs in sand, they would rot. > _______________________________________________ pbs mailing list pbs@lists.ibiblio.org http://pacificbulbsociety.org/list.php http://pacificbulbsociety.org/pbswiki/