Come in from the cold!

[DaveW]

Just been in my unheated greenhouse for the first time for a month or so. Far to cold over the cold spell in there for me so I just left the cacti to it. We did not get as much snow as many of you (only about 4"), but did have a few nights of heavy frost before the snow started, which I felt was colder than when it snowed. I always prefer snow on the greenhouse to frost since it acts as an insulating blanket on the roof.

As the cold spell when it started was worse than I expected I never got around to covering any of the plants even with newspaper, and the greenhouse itself is not lined with polythene, so it was too late to bother after that. Some tender stuff had been brought in the house, but most other cactus genera were left in the greenhouse. My maximum/minimum thermometer, still graduated in Fahrenheit, says it went down to 20F (-6.66C) if I have read it right, I will double check in daylight tomorrow, but so far out or around 800 plants I cannot find one cactus that has died and not even one that has marked with the cold.

I will have to wait until they start growing again to see if they are all OK. So I am tempting providence saying this, but so far there appear to be no losses or damage having endured a prolonged cold spell where temperatures often did not get above freezing during the day for quite a time. The plants are of course dust dry, not having any water since September.

DaveW

[Ross M]

That's great news Dave and reassuring(tu)

My unheated greenhouse dropped to -5C and with the exception of two obvious minor casualties, all looks OK. The bulk of my collection consists of Sulcorebutia and Rebutia, which I've grown without heat for the past 20 years. This cold snap was, however, exceptional in its duration and intensity for many. As you say, only time will tell and I'll feel much happier once growth commences in the spring.

I'm hoping that the only thing which the cold killed off are the mealy bugs and Red Spider Mites! I wonder how hardy these little critters are:shrugs:

[Patrick]

Yes the story here was similar. It did get below -10c outside but never lower than -7c in the polytunnel, under the fleece which was (and is again) covering the plants. I have lost one or two but not really unexpectedly. One interesting thing was that two small Matucana aurantiaca polzii from which I had removed the offsets bit the dust but that one of the same age on which I had left all the offsets (lots) is still hard and healthy. Even Lithops and Euphorbia obesa look fine, some small aloes too. Fingers crossed

[Stuart Estell]

That matucana you sent me has been out in the cold frame, Patrick, where it's not only been frozen, but wet too as water got in. It's still in one piece though!

[CactusGraham]

Same story here (although I did mollycoddle mine with a sheet of newspaper). Like Ross I have mainly Rebutias and Sulcorebutias. My only loss so far has been to a hungry woodmouse that ate all of my seedlings of Astrophytum asterias, the pink flowered variety. Graham.

[DaveW]

I checked my old mercury maximum/minimum thermometer still graduated in Farenheight this morning and took a picture to record the lowest point it reached during the freeze to make sure I was correct.

[attachment 22089 thermo.jpg]

So far I can see no casualties or marking, even with things like Selenicereus, Heliocereus, Astrophytums etc. Time will tell though, but the cold snap has been over for a few days now.

I wonder if the reason we experienced so little damage was that it froze and stayed frozen, rather than the usual British freeze thaw, freeze thaw, we usually get when many plants seem to mark at much higher temperatures? Perhaps it is normally the sun on the greenhouse during the day warming them too quickly if frozen that causes the damage?

With normal cold snaps the greenhouse temperature does not drop long enough to freeze my cacti since sunlight during the day has warmed the floor and beds enough to act like a storage heater to a certain extent. But if the freezing spell is prolonged and the plants do freeze, direct sunlight warming them too quick does seem to cause damage.

DaveW

[IanW]

The biggest problem I'm finding now with my outdoor plants is physical damage as mentioned previously.

No more have caved in at the growing point, but I've noticed a couple more large splits on some off them, even on hardy species. One T. smrzianus in fact has about a 1 inch wide split running from base to top of it and running deep inside the plant to the core, so I'm not convinced there's much hope for that one. Two other T. smrzianus are still fine however.

So basically, apart from the odd species, for those outside, the main damage I am now convinced has been done by expanding ice as it warmed up- just as ice causes potholes in the road, it seems to be able to cause a fair bit of physical damage to cacti as it melts off.

My outdoor plants were all expendable, and I wanted to try and absolutely the toughest conditions possible, so the fact any have survived at all so far this winter is a big bonus. The interesting point is though, that even though some have survived, of those that haven't or are damaged, I believe they would also easily have been okay with just a few simple measures, such as brushing the snow/ice off of them. I believe many of those I have outside are likely hardy down to -20c from the temperatures we got this year (-16c) and so could easily survive a worst case British winter quite consistently if a little effort is taken to protect them, and some will as I've seen so far, survive just fine even without any effort to protect them.

Some may be interested to know that the growing medium doesn't seem to matter too much outside either- I have some in almost pure gravel, and others in a standard 50/50 JI/Grit mix, all in pots also.

It'll take some months before damage can be fully assessed as the injured take time to die and so on, but right now, in one way I'm sad to see any of my plants die, but in another, am pleasantly suprised by the hardiness of those that are toughing it out okay. If much common belief about cacti hardiness was really true then none of them would've made it past christmas even.

[DaveW]

The problem outside can be wet Ian. It will obviously be warmer in a greenhouse too, no wind chill. But your plants will have had wet feet longer than mine being outside in the UK, since we seldom get dry ground in winter. So your plants will be more turgid with thinner sap than mine in the greenhouse which have not seen a drop of water since September.

DaveW