Phoenix Tropicals Gardening

[GermanStar]

Well, I seem to have a final tally now. Euphorbia (covered w/heat source) is fine, one zone 10 Agave has some damage, but it'll be fine. One normal Sansevieria trifasciata (covered w/heat source) has considerable damage, but it lived, another dwarf Sansevieria trifasciata is perfect. A Tropical Bird of Paradise was covered two of the three nights and looks fine. A low temp range of 28° may be a bit pessimistic. The one casualty in all this is my Furcraea macdougalii, it is either severely damaged or dead, time will tell. The plant, which used to be a uniform green, is looking really sad. Many of the leaves were bleeding green, and as you can see, are now looking quite bleached. Every leaf is substantially damaged, and the core looks pretty bad, with two exposed core leaves showing total color loss. I'll give it 10-12 weeks to show me something before I decide to dig it up and replace it with something hardier but far less interesting.

[phoenixtropicals]

Too bad about your plant. You are wise to give it a couple months. Some plants take that long to come back. I'm glad the rest of your plants made it. Tropical birds of paradise are fairly tough. The leaves and stems are good down to 25 F. but the flowers get damaged more easily. My TBP didn't even take leaf damage here when it got down to 26 F. in 2007, so the 25 F. in the literature seems to be valid. I put a chart in my website with damage temperatures for various plants if you are interested in taking a look. I learned a little more about my plants this time around. The coldest night here seems to have been 29 F. and maybe dipped to 28 F. right before sunrise. I'll throw some pictures of my scorched plants on this forum this weekend.

http://www.phoenixtropicals.com/frostDamageChart.html

[GermanStar]

It's hard to tell from the pic, but that guy is over 5' tall, it won't be coming back anytime soon, if at all. If it shows some sign of life, I may give it a chance. Think of an enormous Agave, and the two outermost leaves in the core appear dead. The third leaf may be OK, though it does show some spotting. We're talking many months at a minimum and perhaps a couple years to regain its present form. In the meantime, it's gonna get ugly.

Then there is the long term consideration. It may not tolerate full sun here, and it's already proven less than adequately hardy, so is it worth waiting for a recovery that may never happen, only to fry or die in the not too distant future? I'll decide in early spring.

In regard to the TBP, I thought I had read 28°, and agree that 25° sounds more like it.

[GermanStar]

I had an interesting exchange with a grower recently, who explained that the reason for covering frost tender plants is not to protect them from frost so much as sun. Many frost tender plants can withstand a slow chill (key word being 'slow'), it is the rapid thaw in the morning that kills them. Cover the plants to protect them from morning sun, providing an opportunity to warm as slowly as they cooled to eliminate or mitigate frost damage. For example, my uncovered and severely damaged Furcraea was ghostly pale on the sun side while still healthy-looking and green on the backside for a while. I've seen other examples as well, frost damage is frequently confined to or notably worse on sun-exposed parts of tender plants.

[GermanStar]

Turns out the Euphorbia is damaged, though it still looks fine. There are two plants side-by-side and substantial portions of one are going soft, i.e. rotting from the inside. The other, larger one seems OK -- so far. If that is how it winds up, I'm fine with it. The plants are pretty close to a sidewalk and have been branching like crazy. I would have had to take measures anyway.

[phoenixtropicals]

As far as I know the source of frost damage is that ice crystals break apart the plants cells. Water expands when it turns to ice which is what does the damage. I have also noticed that the sides of plants that got more heat in the summer tend to take more of a beating in a frost, regardless of whether those parts are receiving more sun now (the suns position is not the same as summer now). I'm guessing this is because those parts are more adapted to the heat and are therefore less adapted to the cold. Larger pores on the leaves possibly?

I also think a "slow" chill would be worse. That would mean your plants are subjected to freezing temperatures for a longer period and would more thoroughly freeze.

[GermanStar]

I dunno. I see a lot of references to quick thaw damage online. I don't really think covering plants without a heat source does very much in regard to frost protection (a couple degrees maybe?), but it does protect from a quick thaw. The idea as I understand it, is that after a mild damage-inducing frost, sunlight thaws parts of the plant much faster than others, resulting in nutrient demands colder parts of the plant are not prepared to provide. The result is death or severe damage, rather than the mild damage caused by the frost. I'm nearly certain quick thaw greatly exacerbated frost damage and did my Furcraea in. All the severe damage was sun side, the backside looked nearly perfect for a couple days. In any case, there is an important lesson here -- don't be too quick to uncover plants the morning after a frost. It is my understanding that quick thaw is especially dangerous to trees. Red Belt is one of the diseases found in trees subjected to these exact conditions. Curry & Church 1952: "Damage was frequently most severe on the south and west sides of trees, suggesting that bright sunshine raised the surface temperature and stimulated excessive transpiration under conditions where water replenishment from the frozen trunk was impossible.

[phoenixtropicals]

Seems like there is some truth to that when plants are marginally damaged. I have found once they truly freeze solid they just turn to mush.

[GermanStar]

Ugh, here we go again...... Not as bad, hopefully.

[phoenixtropicals]

Wow. 30 on Wednesday! I find that so hard to believe in February. Thanks for the heads up. We'll see what happens.

[GermanStar]

Lucky you! Fountain Hills forecast is 26°, and that's 500'+ below my elevation. Two or three subfreezing nights again, one likely a hard freeze. Last winter may have been damp and dreary and all around unpleasant, but it never got cold like this!

[phoenixtropicals]

How did last night work out? I am starting a new thread since this one is so long now. You can find it here:

http://phoenixtropicals.com/phpbb/viewtopic.php?p=936#936