guavas can resist -4.4º C if "cold acclimated"

[huertasurbanas]

This is great, but I dont know how to artificially cold acclimate a guava...¿?

http://hortsci.ashspublications.org/content/44/5/1258.full

"The leaf freezing tolerance (expressed as LT50 values) of nonacclimated tissues was ≈–2.5 °C and significantly enhanced to ≈–4.4 °C after an environmentally controlled cold acclimation regime for both cultivars."

"Cold acclimation (CA) is a phenomenon that occurs when the freezing tolerance of plants increases after exposure to low, nonfreezing temperatures (Thomashow, 1999). Almost all temperate perennials and many annual and biennial plants can alter their freezing tolerance when exposed to low, nonfreezing temperatures (Wisniewski et al., 2003). "

[ClayMango]

Holy crap!!!! so bascially..its ok to let your babies get a little chill in the winter if its above 32...will slowly build a small tolerance to colder settings? incredible research!!!

[huertasurbanas]

Yes, it's great, and:

" Thus, LFT (Leaf freezing tolerance) of both cultivars (assessed as LT50) increased after CA by at least 1.9 °C, which was obtained by the end of the 10/5 °C (day/night) step of the CA regime with no further gain in freezing tolerance achieved after 7/3 °C (day/night) exposure for an additional week (data not shown)."

So 10º/5º C (day/night) would be enought for a cold acclimation in the end (they did it for 3 weeks "Plants were exposed to a stepwise lowering of temperatures in the growth chamber as follows: 18/12 °C (day/night) for 1 week, then 15/9 °C (day/night) for 1 week, then 10/5 °C (day/night) for 1 week, and finally 7/3 °C (day/night) for 1 week. ")

[ClayMango]

Yes, it's great, and:

" Thus, LFT (Leaf freezing tolerance) of both cultivars (assessed as LT50) increased after CA by at least 1.9 °C, which was obtained by the end of the 10/5 °C (day/night) step of the CA regime with no further gain in freezing tolerance achieved after 7/3 °C (day/night) exposure for an additional week (data not shown)."

So 10º/5º C (day/night) would be enought for a cold acclimation in the end (they did it for 3 weeks "Plants were exposed to a stepwise lowering of temperatures in the growth chamber as follows: 18/12 °C (day/night) for 1 week, then 15/9 °C (day/night) for 1 week, then 10/5 °C (day/night) for 1 week, and finally 7/3 °C (day/night) for 1 week. ")

I hope this works on Mangos

[Ethan]

My guavas (psidium guajava) took 25F +/- this winter and equally as cold in the past.  Every winter we are below freezing on many mornings and sometimes below freezing for hours.  My guavas loose 1/4" wood and smaller but grow back quickly and have fruited every year.  They are very tough plants and I dont do anything special to acclimate them.

[huertasurbanas]

Yes, neither I do Ethan

Here in our urban garden we use to have -3º C/26.6ºF (the worst temp), 4 or 5 times per winter, a lot of -1º C, -2ºC frosts, etc., they loose all their leaves and some small branches dry.

I wonder if guavas here could flower and bear fruit in winter if protected, what do you think?

Reading this doc, it seems to be possible:

http://www.hort.purdue.edu/newcrop/proceedings1996/v3-451.html

"The four-year-old guava trees established in the field during 1993 and protected from winter temperatures by a 6-mil polyethylene-covered structure (Fig. 1) equipped with two electric heaters, bloomed from Feb. to Aug. 1994. Fruit maturity and tree-ripening followed a similar pattern, and thus, an average of 30 fruits per tree were harvested during Aug. 1994 through Feb. 1995. Fresh fruit weight ranged between 133 and 862 g with an average weight of 390 g/fruit. Monthly yield of guava fruit from 26 trees peaked in Nov. and Dec. (Table 1). Good quality guava fruit was produced during the winter. There have been no incidences of any disease or insect problems. "

[Ethan]

I would bet if you could get your tree through the first few years of cold, it be just fine after that with out protection.

[huertasurbanas]

Yeah, both are growing more than the damages from winter frosts, so as the years go by maybe they will resist much better

[zands]

Strawberry guava is an invasive bush in Hawaii making me think it is tough and cold tolerant. Cold tolerant also going by the way the leaves look and the branch structure. I'll bet it can take temps below freezing for a few nights.

My strawberry guava today. They must be picked red as possible to be sweet This would make a nice hedge

[huertasurbanas]

Yes Zands, they can take -6º C as far as I know, but are different species, SG is p. cattleianum and I was talking about p. guajava, anyway, maybe a grafted guajava over cattleianum could take -6º C frosts?