Unheated greenhouses

[MikeT]

I've now had time to assess the effect of last winter. Having not heated the greenhouse for many years, I thought I’d list some of the pros and cons.
First the good news:
No heating bills
Plants such as Pediocacti and some Echinocerei flower better after cold winter temperatures
No need to worry about power cuts (electric heating) or condensation (gas/paraffin)
Most years you don’t lose any more plants in the winter than if you have heating. (See below under bad news)

Then the bad news:
You have to take tender plants indoors for the winter –bit of a hassle, but not too much for me with suitable space under a loft window
Most years you might lose a few plants in the winter (but not obviously any more than if you have heating). (See above under good news)

However, when we have the coldest December since records began some 100 years ago, there are some extra items of good news and bad news.

Extra good news:
Those labels where the name has faded? Doesn’t matter any more
Plenty of spare BEF pots
That perennial problem of the greenhouse being full? Solved it
Good bit of exercise with all those trips to the compost heap

Extra bad news:
About 85% of the plants dead

Considering how few casualties I had in the previous (2009-10) winter, I was surprised at the carnage this time. I didn’t appreciate at the time how much worse conditions were. Plants that have survived temperatures of -9 or 10C on a number of previous occasions, or spells of sub-zero for days at a time, couldn’t cope with last December.
Some individual plants surprised me. Some 5” Aloe polyphylla seedlings were among the first to go. I thought it was supposed to be pretty hardy. More disappointing was the 18” Aloe polyphylla which took until February to show that it too had perished. Out of many Mammillarias, I now have only 4: M. microhelia, 1 small seedling of M. bocasana (various other seedlings and a large clump all perished), and, appropriately, M. vetula gracilis ‘Arizona snowcap’ along with the usual form.
I didn’t expect to lose most of the Rebutias, including all the large plants: no Rebutias in pots bigger than 2 ¾ ” survived. All Titanopsis perished, some 15 year old from seed having coped with an unheated GH perfectly well in previous years.
Selenicereus spinulosus has survived outdoors over winter for some years, but died after the 2009-10 winter; the larger plant in the GH has been reduced to a few pieces after surgery.
Current GH

2011_03_24_2283r.JPG (95.62 KiB) Viewed 4085 times

[MikeT]

..and the other side. It's an 8x6, all staging and shelves were full

2011_03_24_2284f.JPG (70.13 KiB) Viewed 4084 times

[MikeT]

View in the old days..

15r.JPG (71.75 KiB) Viewed 4083 times

PS the photo resizing seems to be reducing actual size not just number of pixels -I'll try to sort this and re-load the pics

[jfabiao]

Ouch, Mike. That hurts. :\

[Liz M]

That's really, really sad. At least you will have a great time filling it up again but there are always some that you will never replace.

[Tony R]

Sorry to hear of your losses, Mike, but it gives you a great opportunity to re-assess what it is you want to grow in the future, taking account of potential future climatic conditions. Good luck!

[Peter]

If you don't lose them, there's also the possibility of bad scarring. Also, new plants of a reasonable size aren't cheap - all told, I reckon that it's best to heat to 3-4°C.

[Bill]

Sad to see that Mike, by the sounds of you haven't been put off though.

Re pictures, if your picture was physically bigger than the maximum size which is 550 pixels wide it will be automatically resized to that width (assuming it's less than 250kb file size) and clicking on it will bring up a full size image, if they show up as smaller than 550 as some of yours do it means that's how big they are and no resizing has taken place.

Bill

[IanW]

Considering how few casualties I had in the previous (2009-10) winter, I was surprised at the carnage this time. I didn’t appreciate at the time how much worse conditions were. Plants that have survived temperatures of -9 or 10C on a number of previous occasions, or spells of sub-zero for days at a time, couldn’t cope with last December.

I'm not convinced last Novemember/Decembers weather was worse than last Jan/Feb's weather. In fact, I measured lower temperatures (-17.5c vs. -17c) in last Febs weather and it was worse for longer than the November/December weather we got here. I think really the damage was done by two lots of such bad weather in one year. I think many of these plants that survived the earlier weather are fine in that weather as long as it only comes once every couple of years, but twice in one year? I suspect that's the real reason everyone's Cordylines and so forth appear to have died around here since December/November despite making it through a worse spell of weather earlier in the year and going on to look okay in the summer.

[DaveW]

I think I lost about 25%-30% of plants in the unheated 12-6" x 18-0" greenhouse. It is not lined with bubble wrap like yours and plants were just covered for a week or so with newspapers. Lowest temperature recorded on the maximum/minimum thermometer was 14 F (-10C). The main problem unlike most years was the sustained cold temperatures with little sun or rise in temperature through the day to warm up the greenhouse therefore the temperature gradually sank lower over the days.

Larger Astrophytum's died, but small ones came through unmarked and smaller seedling plants often survived better than older larger plants that had stood cold for many years, very strange. Very few Echinocereus were lost and are now doing well again. Not noticed any flowers on the small Tephrocacti yet I would expect to like such conditions. The large pachanoi/bridgesii type Trichocerei were devastated, but T. schickendantzii came through unscathed and is budding up.

I agree bringing delicate plants into the house can be a chore, but when you see the savings on the heating bills it is worthwhile for larger greenhouses. Probably we all need a small heated greenhouse and a larger unheated one, or maybe even just a heated "cold frame" within the larger unheated greenhouse?

One of my problems was I re-potted some plants late on last year so that may have added to the losses.

DaveW