Unheated greenhouses

[Aiko]

I agree bringing delicate plants into the house can be a chore

The trouble is not so big, I would say.

I carry in everything I have in my greenhouse of 3,5 meters by 8,5 meters. That will cost me about 3 to 4 hours of carrying plants up the stairs. You can spread this over a few days, if you foresee the freezing temperatures at night and you have the time. I usually bring them in in the end of November. And back again at the end of March. And I will not have any worries for the rest of the winter, will not have heating costs (almost all of them are in an unheated room on the first floor, not getting any lower than 3 or 4 degrees C on the worst winter days), and it is easier to check your plants for trouble. Or just to look at them. Going outside to check on them is much more a burden, I would think (that's another con of keeping them in the greenhouse!).

I really can recommend bringing the plants inside if you have the possibility!

[Ali Baba]

I had a similar experience to Mike in my unheated GH (which is not lined with bubble wrap, and just to add to the insult has the side vents left open a bit even in the winter, day and night). Last Jan I recorded the lowest temp of -8C and most plants survived, and flourished last summer. This year -12C and a completely different story.

Most Rebutias died apart from one or 2 small ones, several S. American opuntiads died including Tephrocacti (though not T. molinensis), and all my Agaves died, as did Neoporterias, Mammillarias, Lophophoras. Also lost Echinocereus viereckii v. moricalli, and E. knippelianus.

Survivors included Epithelanthas, Opuntia santa rita, basilaris, polyacanthus, many Echinocerei (triglochidiatus, polyacanthus, coccineus, salmdyckianus, reichenbachii, viridiflorus, adustus), Leuchtenbergia, Chamaecereus, Lobivia. My large plant of Echinocereus polyacanthus seemed to love it as it produced about 20 buds this year compared with the usual 2 or 3! Unfortunately they all aborted in the searing heat a couple of weeks ago
Maiheunia poeppigii of course grew happily through the winter and was watered every few weeks even in the freezing weather.

There seems to be a bit of a North/South America divide to the losses. The one real surprise was Peniocereus greggii, which has survived happily.

On the plus side if you like North American Echinocerei (I do) then it seems you can grow a fair few of them quite happily without any heat.

[Vic]

I also lost a large Aloe polyphylla Mike, think the problem with this winter wasn't necessarily low temps but the fact that everything froze solid for a couple of weeks in December, even the rivers. Instead of the normal freeze/thaw that plants have endured during previous winters, they sat there frozen for 2 weeks or so. Non c&s related, I lost a large Dicksonia antarctica which I was most upset about, the fronds just simply failed to appear this spring which was the first sign of any problem but unfortunately its no more. The usual precautions were taken with a thick layer of fleece inside the growing point/crown which was more than adequate during the winter of 2009/10 and previous winters. I noticed that everyone seemed to have lost their Cordylines also including some large multi-branched specimens which must of been many years old, Phormiums too seemed to of met a similar fate. With hindsight more precautions and frost protection could of been taken but unfortunately plants don't tell you until its too late!

[MikeT]

Vic, I've also lost a few garden plants that I wouldn't expect to lose. Cordylines seem to have suffered badly in Sheffield, dead ones all over in gardens and in civic plantings. Noticed lots of dead cordylines on recent trips to Nottingham and Birmingham as well.

I think you're right about the prolonged freeze. I find Escobaria vivipara will take dry cold but not wet cold; in the northern part of it's range, it copes with temperatures lower than it will get here, but the pattern will tend to be freeze and stay frozen for months, then thaw in the spring. Most of the other plants we grow will cope with very low overnight temperatures but then warm up in the day. They really didn't like the prolonged sub-zero that we had last December. At the time I didn't realise how very different conditions were, I just went by the lowest temperature and thought "they've coped with before, including last winter, they'll be fine".

I've been quite enthusiastic about growing cacti in an unheated GH until this year. The difficulty is in knowing when the next similar winter will be. If not for 100 years, I'll risk starting plants from seed again. I can't face the thought of the same happening again in 10-15years though. By then I'll be getting to an age where sowing seed for 10-15 years ahead will be a shade optimistic. We seem to have had a lot of "coldest/wettest/dryest/hottest" specific month on record in the last few years. "Global warming" could well mean more extreme weather, rather than mild winters and hot summers, at least for us in the UK. Time has come to get a power supply fitted, even if I only aim for frost free.

[lobman]

Like many others ,I have lost many plants over the past couple of winters ,about 1500 , and will try to revert to my old system of winter heating - heating cables and hoops over the staging top covered with fleece , which I found the most economic as only the minimum air space is heated ; however as the greenhouse had to be filled with plants before my " proper " staging was built it is no easy task .
The main angst is caused by the fact that so many plants with data are hard to replace , as its a task to find equivalents

One thing that I have noted is how the low £ has put up the price of seeds , I can remember when it was possible to buy four or five packets for 1 £ , now its 80 p per packet , so I will be selective about what I need .

[BrianMc]

Just to add some thoughts from my perspective in Central West Scotland.

The vast majority if not all of the Cordylines and phormiums growing around Glasgow died in the winter of 2009/2010, so I am unable to use the cordyline bench mark of winter worseness.
I had far colder periods in 2009/2010 than 2010/2011. The bad thing I found about the last winter experienced was the length - October 2010 until March 2011. The Winter previous started proper in December 2009 and ended in March 2010. A positive regarding all the frosty weather is that we have experienced much more winter sunlight. The worse part of Winter 2009/2010 and what killed most outdoor plants was not the clear, crisp -17C spell, it was the -7C freezing fog which lasted a few days - making wonderful photo opportunities, but effectively encasing plants in ice!

Regarding small pots, seedlings and better survival. My opinion is that younger growth is far more 'vital' than older growth and much more able to recover from knockbacks. Another reason is that small pots are capable of taking advantage of the vagries of microclimates that may exist. A single headed rebutia will have air moving around the body, allowing a frozen plant to defrost quickly. A big clump of frozen rebutia is more likely to stay frozen longer as the thawing effect of the circulating air will not be present.


One question Mike...
As you have not used any method of heating in your greenhouse why did you go to the expense of installing bubble wrap. Would it not have been more prudent to spend the money on horticultural fleece? Clean the glass to allow all winter light in and cover the plants with the fleece each night, removing in the morning? Perhaps survival rates would have been higher
Good luck for next winter!

[iann]

Following the crazy cold snap in winter 2009/1010 I now have an emergency heater but most of the time the greenhouse is unheated. It isn't insulated, since as Brian mentioned, insulating a greenhouse with no heat source inside is just blocking out good light for no reason.

This winter I dragged in anything not extremely hardy in late November or early December when it looked like it would be very cold for quite a few days. They didn't go back out for over a month! The few tender cacti I have had already come in weeks earlier. I lost very few cacti and none that I would really put down to the cold, just the typical random die-offs.

Although temperatures throughout December were well below freezing just about every night, they reached well above freezing just about every day because of all the sunshine. I couldn't even keep snow on the roof for protection from the impending hard freeze!

I did lose quite a few succulents, some that were deliberately tested for hardiness (Lithops bromfieldii seems to be the most tender Lithops), some that I thought were hardier than they obviously are, and some that got caught out when the cold first hit. Many things in the garden died, but not all.

[CactusGraham]

Hi Mike, Yes it's tough losing so many plants. I too have lots more space now. The total of my casualties currently stands at just under 200 plants. I'm convinced that the damage was caused by the plants being subjected to sub-zero temperatures in November, before the plants had time to dry out. The largest plants were the ones that suffered most, as most of my 1, 2, and 3 year old seedlings got through the winter unscathed. I have grown plants in an unheated greehouse for several years, and have lost very few plants previous to this winter. I had chosen to grow plants that should be okay in those conditions, but I have lost dozens of mature rebutias, sulcorebutias, gymnocalyciums and mammillarias, plants that have been with me for up to 20 years. I buy very few plants as I get a great deal of pleasure from growing from seed, and once I start potting up my seedlings, it won't take long to fill up the gaps. Good luck with your plants in the future.

[Ross M]

I got off really lightly as I only lost a couple of my large Rebutia collection in the unheated greenhouse. It really was like a deep freeze - day after day of sub-zero temperatures which never rose at all due to the greenhouse not being in a location to receive any sun from late Autumn to early spring. So it was as cold in there during the day as any shaded area outside

My experience with mature Sulcos. in particular has led me to believe that whilst the exposed plant body can endure freezing temperatures, the roots are considerably less hardy. Any losses that I have had over the years has shown that it's always the roots that go first, with secondary rot spreading up through the vascular system into the main plant body. If you think about it, a plant growing in the wild has its roots insulated within the earth whereas a pot grown plant in cultivation has it's roots more or less exposed to the elements! I reckon that putting the pots in polystyrene fish boxes or similar would certainly help.

If you're lucky and notice the tell tale discolouration of a plant that has frost damaged roots, you can often salvage a few offsets. I've even managed to save a 1/4" thick half slice (all that remained rot-free) from the top of a large arenacea by grafting.

[Chris L]

I reckon that putting the pots in polystyrene fish boxes or similar would certainly help.

I tried that. Abandoned the idea when I found a cat sat on my staging...