Drainage in pots

Alberto Castillo ezeizabotgard@hotmail.com
Thu, 17 Feb 2005 16:32:27 PST
“What about pots plunged or placed on sand so that the soil in them
is in capillary contact with the sand? I used to have ordinary terra
cotta pots plunged in sand (placed over the soil) and was of the
opinion that the sand bed blotted up excess moisture after watering,
while providing some moisture when things started to get dry.
The key element being that the pots had no crocking in the bottom and
were wrung into place so that there was capillary contact between the
soil in them and the surrounding sand bed through the central drain
hole in the bottom of the pot.”

Dear Rodger:
I owed you a response. Hopefully everyone has read that useful Jean’s 
Canadian resource on water vertical movement in pots, specially the many 
newcomers to this exciting site (PBS of course).
For one thing. nothing can beat growing bulbs in the ground, say in raised 
beds for instance. But it has practical problems that are not easy to 
overcome. One step forward is the use of pots plunged in several possible 
materials. The aim of this plunging is to mimmick soils’ mostly constant 
temperatures. It also provides a  very effective protection against slight 
frosts.. Plants (except those from deserts) hate changes and clearly prefer 
to live in environment conditions that remain rather constant.
It is not that the plunge material blots the moisture from terracotta pots. 
Moisture escapes through the porous walls wether plunged or not. The reason 
for using a plunging material is another as said above. Most often people 
fails to see  that this release of moisture thru terracotta creates a 
refrigerating effect that lots of plants find very stressing. Obviously 
tulips, hardy Ornithogalums, Gageas or Fritillarias will love this coolong 
process but Zephyranthes, Cypellas, Geissorhizas or Hippeastrum can only 
really stand it while they can. They are a lot better in plastic than in 
terracotta. But since plastic does not lose moisture thru the walls water 
remains in them for longer. As a result, most bulb and succulent growers 
have heard that plastic is bad. What is bad is the practice of using 
unsuitable draining holes.
One of the greatest bulb experts in the world, Jane McGary, uses plunge beds 
for her bulbs and has written a most informative article on this system. I 
have used this system for over 20 years with success but now I have moved to 
a different method (really big containers) that gives amazing results.
All the best

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