Raised beds and capillary action

John Lonsdale john@johnlonsdale.net
Mon, 05 Jul 2004 15:30:26 PDT

Harking back to my old days of growing high alpines and bulbs in pots, there
was a common misconception, still propagated now, that it is important to
have drainage material at the base of the pot.  This is nonsense, the only
place that drainage needs to be is in the compost - and the same holds true
for raised beds.

I suspect your compost itself isn't well enough drained, 18" of raised bed
should be way overkill to defeat capillary action, especially given
evaporation from the surface and sides of your bed.  Most of my raised dry
sand beds here are 9" high, the maximum is 12" at the front.  By the middle
of a normal summer they are dry down at least 4", more than enough to keep a
wide variety of bulbs happy.  The Onco bed was only covered today with 8x4'
sheets of twin wall PC, at a height of 12".  I have some self sown Dicentra
peregrina seedlings in one of these beds and their roots go down at least
2-3" - I had to water them yesterday because they were keeling over from



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