heater disaster :(

[pontus]

Hello everyone..

this morning, when I got back home after being away for a few days, I discovered to my horror that the radiator I had placed in my garden shed to maintain the temperature at about 10 or 15°c for my tender bulbs, had broken

sadly, yesterday night was the coldest night of this autumn/winter, with -6°c. I opened the door, and found my worst nightmare...pots frozen solid, leaves frozen on the wintergrowers....ice on the windows...a real carnage!

I quickly found a new radiator, which i brought in and blasted on full blast...

pots slowly dethawed...some where only half frozen, while others completely. I dont know for how many hours they had been frozen, but I now fear the worst for my tender bulbs which where in there. Ammocharis, brunsvigias, haemanthus, nerines, crinums...

do I have any hope? would any of these bulbs have survived, and if slightly damaged, what can I do now? some of these resent disturbance, so i dont really want to dig everything up to check..of course, i can poke around in the pots...but some bulbs are deep..so its a bit hard.

I know some sp experiece short frosts in the wild, in south africa, when soil is dry...so I may have a 1% chance with some...

has any of you had this problem before? and if so, what where the consequences?

Pontus

[Ezeiza]

Although this could be described as a mild cimate there is the occasional frost problem, like if after a storm the tunnels' covers had been blown away, etc. In such cases, we fill watering cans with hot (almost boiling) water and water the frozen pots with it, as early as we can. Of course with the low morning temperatures and the effect of the frost itself the water that reach the pots is not really hot. If we used tepid water it would end totally cold while watering the pots. This applies to partial damage but if caught on time, many bulbs can be saved.

[Gene Mirro]

My experience is that the damage is minimized if the soil temperature changes very slowly.  A very slow freeze is much less damaging than a fast freeze.  A very slow thaw is much less damaging than a fast thaw.  This is why tender plants on the west side of the house will survive, but those on the east side will die.   Because plants on the east side get thawed quickly by the morning sun, but plants on the west side do not thaw for many hours.  This is also why potted plants are killed before plants in the garden, because the pot freezes (and thaws) very quickly. Even frozen food is better if it is allowed to thaw very slowly.  Pontus and Ezeiza, you are both thawing the plants very quickly.  I don't think it's a good idea. 

The other question is, what minimum temperature will the plants survive?  If you go below this temperature, the rate of change doesn't matter anymore.  They are dead.  It is often true that the soil around the bulb can be frozen, but the bulb is not frozen, because the bulb tissue has a freezing point below 0C. 

It is guaranteed that horrible things will happen to your plants as soon as you leave home.  You can minimize the risk, but you can't eliminate it.  One thing you can do is place two thermostatically controlled heaters in the greenhouse.  If one fails, the other one keeps working.  This is called dual redundancy in the engineering business.  But if the electrical power goes out, you are finished anyway.  Maybe the best thing is to have a friend watch your plants while you are gone.  This works sometimes.

[Gerry Webster]

The other question is, what minimum temperature will the plants survive?  If you go below this temperature, the rate of change doesn't matter anymore.  They are dead.  It is often true that the soil around the bulb can be frozen, but the bulb is not frozen, because the bulb tissue has a freezing point below 0C. 

I had never thought of this but it  is clearly true in principle; the inorganic & organic materials of the bulb will depress the freezing point of water in the cells of the bulb & it is this freezing which does the real damage. Some animals can withstand extremely low temperatures (below freezing); there must be comparable information on at least some plants. Does anyone know?

[Ezeiza]

Gene, my interest in such cases is not to eat the bulbs but stop the freezing process, preferably before the sun reaches the foliage for apparently frozen dead foliage will recover with hot water in the first hours. The freezing process is gradual and my aim is to stop it before it kills the bulb. The change of temperatures is very slow hence the difficulty in reaching the proper temperature INSIDE the bulb to clean it virus free.

[Afloden]

I don't grow that many tender species in my greenhouse anymore, but I do still have Brunsvigia radula and orientalis, several Haemanthus, many Nerine spp, (but no sarniensis), and a few Crinum from AU (all SA spp planted outside).

I usually only turn on heat in my greenhouse when night time temperatures start getting below the low 20's F (-6C) which is about what you experienced. Was that low the inside greenhouse temp or the outside air?

I have let all those SA genera have their pots freeze at least a few times over the past 6 years and never had a loss of one due to cold. The soil does not have the same sugars in it that the bulbs do so it freezes far quicker than the bulbs will. The bulbs need sustained cold temperatures to freeze though some young bulbs will freeze quickly. A slow though is best as a quick thaw will burst the cell walls as will a quick freeze on over hydrated (sugars diluted) plants.

 All my Ammocharis are planted outside but I only grow coranica. It is bone hardy for me in full sun and loose soil in a raised bed. All South African Crinum are planted out as well, but I only have a handful.

 

[pontus]

the temperature outside was -6°c, when I checked the thermometer inside the garden shed when I arrived at 10 am, it was about -3 or -4°c. as aparently there was no frost the day preceeding this night frost, I imagine the -6°c was reached gradually, from about 11 pm or midnight onwards...so it was probably a gradual freeze which must have persisted for a few hours.

It is iterestig to hear about the  gradual dethawing....i dont know how quick my pots where to dethaw, but when I went back to check, 4 hours after putting in the new radiator, pots where still frozen...but then, at night, most had dethawed...

I will be trying to check over the past few days on surviving bubs, but as it is still cold during the day, i dont want to risk bringing plants outside to check them

I did have a hymenocallis littoralis pot that got badly frosted 2 years ago, outside, with a sudden unexpected frost, at -5°c. I brought the pot indoors, and cut off teh frosted dead leaves.. Eventaully, when all hope was gone..after a few weeks, a small, new leaf emerged from the centre of the bullb, and it then slowly regrew over several months, and although a bit weaker that season, still grew ok and survived..so maybe there is hope.

It is interesting to hear about the hardiness of amocharis in the ground...

Pontus

[Richard Green]

I think the reason that slow freezing is safer is that smaller ice crystals form, and these are less likely to damage cell walls.  Also water expands as it freezes, and slow freezing allows cell walls to expand slowly rather than bursting.

Likewise the reason that slow thawing is better than fast is that the structure of the plant becomes flaccid as the ice melts to a smaller volume of water and the cell walls have time to return to their previous size slowly rather than causing bends and kinks in stems and structural collapse which follows a fast thaw.

Pouring boiling water on pots will start thawing them quickly from the outside and is likely to cause considerable damage to bulbs near the edge, and to any foliage above the surface.  I think that length of time frozen is much less important than the slow movement of temperature through the freezing zone in either direction.

Clearly some plants are designed not to be able to cope with any freezing at all"

Do we have a forum scientist who can comment further?

[Ezeiza]

Richard, then all this theorical speculation is true and the many plants saved through the hot water bath are not. My intention was not to start a debate on a proven fact but to suggest Pontus a first aid resource when a catastrophe hits.

[Richard Green]

Indeed, Ezeiza, if disaster strikes me, I like to think I shall have the courage to try several different treatments and compare survival rates later.  I hope never to have to do this!