On Sun, 12 Dec 2004 06:58:25 -0000, "Amber Ormerod"
wrote:



I have a 10x10foot greenhouse aprox 1/4 is bubble wrapped for the cacti and
has a electric fan heater. The rest of the greenhouse is not heated. I have
a vent oposite the door and auto vents in the roof which are not opening at
all atm. The days here (Hampshire) have been very damp for at least 1/2 the
week. I leave the door open for ventilation but thats frequently doing
nothing as its damp outside too. I have had a few days warm enough to dry it
all out, but on a whole I have things like wooden plant stakes going mouldy
already! I have some of the anti damp crystals in the cacti section, but
there is not really a problem in there. I wasn't sure if the crystals woudl
work out too expensive or do nothing in that space?


I have little faith in these anti-damp crystals. IME there are two
types: silica gel, often found in small packets in boxes of
photographic equipment, and what I think is anhydrous calcium chloride
that slowly absorbs water and becomes a syrupy liquid (in fact it's a
strong solution of calcium chloride in the water it has absorbed).
Although both are fine for desiccating small enclosed spaces of a few
litres, they have limited capacity and rapidly become exhausted
especially out in the open such as they would be in a greenhouse. Most
silica gel has a few 'indicator' grains in it, which are bright blue
while it's still active, but which turn pink when it's exhausted. It
can be re-activated in a hot oven, but you'd need to do that at least
daily I would think, and have a large amount of gel well distributed
around the greenhouse and keep it closed up - forget it!. You'd be
better off with a proper electric dehumidifier, but that would be a
trifle absurd (although not as absurd as using anti-damp crystals IMO
:-) )

Mould doesn't flourish in moving air. Can you run your electric heater
on a 'fan only' setting? If so, keep it running all the time to
generate some air movement. Floor-level vents are also a help, but
many greenhouses don't have them. You mention a vent opposite the
door. Is this in the part separated off with bubble-wrap, and if so,
does it mean that through-ventilation is restricted?

Many plants will cope with the minimum of water over winter. The less
you water them, the less damp is the greenhouse. Provided your cacti
are bone dry at the roots (I don't water mine between the end of
October and the beginning April) they will take some cold. It can get
quite frosty in desert areas at night, but it's a dry cold. Do your
cacti really need the bubble wrap, if it's inhibiting air circulation?
IME a closed greenhouse will give a 2 or 3 degree advantage over the
outside temperature on a cold night, and I wouldn't have thought you'd
get many frosts in Hampshire so low as to be a real problem. On those
few occasions, run the heater, and because those occasions are few,
the cost won't be excessive.


--
Chris

E-mail: christopher[dot]hogg[at]virgin[dot]net