Greenhouse temperatures over winter for cacti and aeoniums

[Purpletaz]

Hi
I've been reading comments about greenhouse temperatures and this will be my first year keeping cacti in a lean to greenhouse in south facing garden in fareham in hampshire. I was going to aim to keep it around 10 degrees with a paraffin heater what are your thoughts? Also im keeping my aeoniums indoors again this winter but was wondering what temperature would be safe for them in a heated greenhouse over winter? Does Anyone else keep aeoniums in a greenhouse over winter?

[Paul in Essex]

The minimum temp needed by cacti is extremely variable as the family is spread over nearly all the length and breadth of the Americas, from Patagonia up through to Canada, offshore into the Caribbean, from cool temperate climates to fully tropical. Some can take many degrees below zero, especially if dry, some need a minimum of 10C so it would be helpful if you could list the plants you have for some more precise advice.

I have always kept my aeoniums 'just' frost free - so a minimum of around 3C- without any difficulties. You have to keep them a touch drier. Many seem happy enough with unheated glass but I haven't carried out exhaustive empirical tests to be able to list which. A handful, albeit a small hand, I grow outside.

[Peter]

Will the lean to greenhouse be insulated? Hopefully you will be at least able to insulate the roof. However, south facing in the south of England, somewhere about 5°C should be OK. I keep mine at 4°C but you may like a little more assurance. The Aeoniums should be OK at that temperature.
Paraffin's a problem re so much water being produced. It would be far better if you had an electric heater with a thermostat. It could possibly be cheaper!

[rodsmith]

I would also recommend an electric fan heater. I have mine set at 5 degrees C which I find keeps my conservatory above 3 deg C in practice. The danger for succulent plants in winter in our climate is damp and a paraffin heater will produce a lot of moisture. I have a broad range of cacti and succulents and have had few casualties over the years under my regime. If you keep plants such as melocactus and epiphytes you will need warmer conditions however.

[Paul in Essex]

What they said - electric heater all the way. Paraffin heaters are horrible - aside from the water vapour issue they are smelly, dirty, unreliable, imprecise and expensive to run - especially if you are considering running it at a high temp. Plus you have to keep all the, ahem, 'paraffin-alia' somewhere the rest of the year and it is smelly.

[Purpletaz]

Interesting comments thanks. The paraffin heater hasn't actually been delivered yet so will be sending that back and getting an electric one! Thanks for the guidance on temperatures for aeoniums too. I have some that are a really good size now and didn't want to risk losing them!
Most of the cacti I have I researched would be fine in unheated places over winter but I do have one pot with a few tender ones in so will research them further.

[Eric Williams]

Hi purpltaz, I to agree with the above comments. Electric is the way to go with budget plug -in thermostat. Aeoniums, other succulents and cacti are kept at 5degrees with no insulation.ps make sure heater is connected safely with a rcb if possible. I think these days a socket is available with internal protection built in , not for certain as I have been out of the trade many years now. Cheers

[KathyM]

A lot of cacti are fine in an unheated greenhouse. I put anything that likes to be a bit warmer in a heated propagator set to 5°C. Anything that needs to be warmer than that goes on a windowsill. I'm going to test some plants in a coldframe this winter.

[Conrad]

I'm increasingly of the opinion that a really decent cold spell is a positive thing for many cacti. Over the beast from the east I kept a tray of gymnocalcium, astrophytum, acanthocalycium, denmoza, rebutia and melocactus dry outdoors. The melocactus all bit the dust, but all the others grew and flowered much more strongly this year than identical plants kept at about 6c in the polytunnel.

This year I'll be hearing the tunnel to 2c, and have a mini greenhouse within the tunnel which will be at 8c for the melocacti and matucana etc.

I have a large gas system for the tunnel, but for smaller areas (including my greenhouse within the tunnel) would also very much recommend the inexpensive electric fan heaters. I've had the most consistent luck with them set to constantly run, but then plugged in to an thermostatic plug socket, which seems much more consistent.