Raised beds and capillary action

Jim McKenney jimmckenney@starpower.net
Mon, 05 Jul 2004 14:54:07 PDT
Dear All:

For several years I've been experimenting with raised beds for growing
summer dormant plants here in Maryland. I've been building these beds
higher and higher to enhance the drainage. Last autumn I build another
raised bed about eighteen inches high. The sides of the bed are bricks set
without mortar - in effect, a dry wall. No proper drainage material was
used at the base of this bed - I thought the height of the bed and the
leaky walls would be sufficient to allow the sharp drainage I wanted. 

In late May and early June sections of this bed were covered with panes of
glass (actually discarded glass doors) in the expectation that that
arrangement would be sufficient to keep things dry. The glass is several
inches above the soil surface, so there is plenty of air circulation. The
surface of the bed looks dry and even crusty. Yet certain lusty weeds
seemed unphased by the lack of water. And when I dug down an inch or two,
it became apparent that there is plenty of moisture still in the soil. In
fact, I checked a small sample of tulips and frits in this bed and found
that some had already rotted in the hot, damp soil. Bummer!

Obviously I need to change something. I'm assuming that capillary action is
causing water to wick up into the bed. I'm thinking about putting in some
sort of vapor barrier at the base of the bed, between the medium in the bed
and the ground soil.

Does anyone have suggestions about this? 

Jim McKenney
Montgomery County, Maryland, USA, USDA zone 7, where it has rained so much
during the last month that you would think the soil pathogens would have
rotted, too.  

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