Winter is coming. I need a strategy

[ArronOB]

Hi. I’m trying to work out what to do with my orchids, with winter on its way.

Some background. I live not far from Sydney, Australia. We are new in this area so don’t really know what the winter microclimate will be like. I know we won’t get frosts, but I think we’ll see a few nights nights down to about 46degrees f. - just based on where we lived previously.

I have a collection of about 35 small cattleya hybrids, mostly in 3 and 4 inch pots, and about 30 large oncidium alliance hybrids, mostly in 6inch pots. I keep these in a little shadehouse - timber frame covered with shade cloth all over. They have grown very well through this summer, so obviously it suits.

The oncidium types I’m happy to leave in the shadehouse through winter. They’ve overwintered outside before with no problems.

The cattleyas I was expecting to bring inside and grow on the windows in the unheated parts of the house, which will get down to about 57degrees, I think. Now I realise how little space there is, largely because they have grown so much larger over summer. So I’m thinking I may have to leave all or some where they are, and modify the shadehouse so it’s a bit more winter-friendly.

So my questions are:

Is it practical to line the shadehouse with plastic sheeting. Will that help keep the temperatures up. If so, what type of plastic should I use - or is all plastic film much the same in terms of light transmission.Is there anything else I can do to keep the temps up without using electricity. If I line with plastic, will there be an issue with ventilation - should I provide openable vents and open/close them as appropriate.

Or is this just a dumb idea. Maybe there is a better solution.

I don’t want to build a better greenhouse at present, we will be building a new house soon and don’t want the complication.

Cheers and thanks
Arron

[Orchid Whisperer]

The occasional night that dips to 46 F should not be a problem for Cattleyas, even with out plastic tarp. Don't water on days where you expect those dips. Water early in the day, if you can't do watering early, it is OK to skip.

If you have colder dips, and can toss a tarp over your shadehouse, do that. Or if your plants are on a bench or plant shelving, you can toss a tarp over the bench. That may be enough. If you can get a really safe space heater, such as an oil-filled one, that might be used on colder nights if you can protect it from water. You can put the heater on a timer to only come on during the coldest night temperatures. The heater is only for the rare coldest nights.

[Optimist]

I actually think that going to 47 on occasion is not terrible, however, I would be a bit worried as well-- just in case your weather service is wrong.

A "greenhouse" plastic sheeting qualifies, often keeps the place at about 10 degrees higher (in Feregnheight). If you get spooked, there are various outdoor heaters which do not cause problems if you keep flammable objects away from them. For instance, look up a flowerpot heater, which is a large terra cotta flowerpot upside-down (like a hood) over a ceramic tile or other fire-proof flat surface. You get a can of sterno, or a 24 hour (long burning) candle, light it, and put the flowerpot over it. In most cases this will warm a small area up very nicely overnight until the sun comes up.

I would not use this in the case of a tornado or anthing that could upturn the candle. You could also heat with an oil space heater and have a long exterior outside extention cord going out to the shadehouse covered with plastic (if it is only night, you can cover also with blankets, and take them off in the morning). I believe there are also "outdoors" heaters meant for more watery areas.

So there are several choices.

[Roberta]

I really don't think that winter will be a problem for you. I am about as far north as you are south, also on the coast, and I grow about 90% of my collection outside all year around. Occasional nights close to freezing ( 2-3 deg C) but not for very many hours - warms up by day. Orchid Whisper's advice is spot-on. If cold, don't water. A dry orchid can tolerate much lower temperatures than a wet one.

[ArronOB]

Ok, thanks for the replies. Based on this advice I think I’ll put some plastic sheet over the roof to keep the rain out and otherwise see how they go.

Cheers
Arron