This is one of the worst things that could happen late in the winter. An unwelcome arctic blast. For the past ten days we have enjoyed extremely pleasant 70's spring time temperature. A lot of my citruses were coaxed to form flower buds in response to the warm days. Come wednesday night, the day after valentine's, it will suddenly be colder by 20 degrees F both for the highs and the lows.

Citrus should be able to take even subfreezing temperature, but the sudden diversion of the jet stream, there is no time to adjust for cold hardening, especially that they are starting to bloom out. It is going to be wipeout. The only hope is a miracle for the winds to change direction. The sudden cold blast is the most damaging to citruses.

My unique citrus collections are all in the process of blooming and is looking forward to the fruits the first time. Will try to cover them with blankets come Wednesday pm.

http://nimbo.wrh.noaa.gov/warnings.php?wfo=sto&zone=CAZ017&pil=XXXSPSSTO&productType=SPECIAL%20WEATHER%20STATEMENT

for those in California, just change the city and state of the link below to see if you are affected with the cold air.

http://nimbo.wrh.noaa.gov/total_forecast/index.php?zone=caz017&county=cac067&wfo=sto&dgtl=1&lat=38.58167&lon=-121.49333

The forecasts for Santa Rosa currently vary from 32F Wednesday night to mid 20'sF. Not good. My Cara Cara, Algerian Clementine, Tarocco, Bearss Lime, and rootstock (ex. WA Navel from C&M nursery) are all in flush. My Dancy, Valencia, Meyer, and Owari Sat. are showing initial signs of flushing. Not yet decided if they are just going to go back under the eaves on my deck or if I need to clear space in the shed for them.

To make matters worse, last night my grow light fell on top of my stellar growing Moro seedling. Patient appears to be stable, but too early for accurate diagnosis. Oh well, my own fault. I knew my improvised hook mount was dubious at best.

Kent

We had our coldest night of the year so far here in N/C Fl last night. We hit twenty one for a while so I'm sure some of the leaves of my orchard citrus are crisped now, but probably not any significant twig damage (I hope).

Fortunately between the two 250 watt IR bulbs, the seed heating mat, and the blankets I threw over the top my green house stayed right at 40 for the low temp of the night. I've had really nice growth and myriad blossoms on my Tahiti limes, Eureka lemon, and Key limes and sure would hate to lose that. Also have a lot of seeds in flats in there as well.

.....Alan.

The lowest it has hit at my place this year was 28 last night.I haven't protected anything this year & have new growth on my Navels, Harvey lemon, Bloomsweet Grapefruit and even my Key limes.

Just for the record I planted Key lime seeds in March of 2004. From the looks of it two of the plants have developing flower buds. Thats a record for my seedlings two years !

Now the dew point has dropped to 25 deg F! My citruses are in real trouble. When dew point temperature drops, a definite cool down is on the way, and it is the most accurate basis of predicting the lows within 24 hours. Needless to say, it is going to be 30 deg F.

If this happened earlier, like in January, all my plants are cold hardened, and they could take it, even down to 25 deg F, without a scratch. But with flush of blooms, a light frost could wipe out fruit production, if not damage the small limbs that have awoken.

I have less than 24 hours to come up with a very efficient method of protecting these trees. I am at odds with strong winds, so the canopy covering like a blanket sheet is not a good option at the moment. Perhaps good old Christmas lights on the top and coffee can covered kerosene lamps below.

Since the major source of damage in citrus subjected to sub freezing temps is dehydration, you might be able to spray the trees with water to prevent it. I know this is what they did in Florida when I lived there 2 yrs ago.
Andi

cold tonight in Oregon Brrrr .. I brought all my Plants in the house that where in containers ..
the kitchen is loaded hardly any room to walk and now my cat thinks the big tree is a potty LOL i love plastic wrap ..Tammy

Good luck in cali its gonna be cold Hope the plants are all safe

Two major types of injuries can be caused by low temperatures in tropical and subtropical plants.

One such direct physical damages are due to the formation of the ice crystals that ruptures the plant tissues. We know that ice crystals can damage the cells nucleus and cell walls and the integrity of the cells.

Another is the chilling injury caused by photo-oxidation. When the metabolic processes are slowed down by low temperature in the presence of sunlight, chilling injury happens. As the sunlight hits the cholorplasts and excite the electrons, the receiver are simply asleep due to low temperatures or metabolically inactive. With the excited electrons nowhere to go, it causes damages to surrounding tissues. It is like having a hot torch around with no one to pass through down the assembly line of photosynthesis, so it burns anything around it. This is what we call chilling injury induced together by presence of light and low temperature. It is more indirect than the damages done by ice crystals physically damaging plant tissues.

Now back to dehydration. My context here is only partial dehydration, not to the point of permanent wilting point or killing off the plants. I think partial dehydration is not the cause of major damages to the citruses during a freezing event. In fact dehydration should help plants tide over freezing temperature. How? Simple physical chemistry. What happens during dehydration? Solutes in the tissues gets more concentrated, and the higher the solutes, the lower is the freezing point of the tissues which would help the plants tide over some marginal cases. A very old evolutionary mechanism used by cold hardy plants that survive freezing temperatures compared to water. They have higher solute contents. Remember that we are talking about survival here, and not growing when conditions are freezing. I mean to imply only short term survival. When long term conditions are involved, that would be a different matter. Now the plant has to deal with availability of water. The very reason why the mechanism for drought tolerance and freeze tolerance are the same, it is coping up with the availability of liquid water.

Artic blast here also. We are slated for 4 days and nights of freezing rain/sleet/snow and all days and nights below 30 degrees. My trees are all inside and IF we loose power I have a kerosene heater for emergencies. . I will just drag them all into the livingroom where the heater will be.
Andi

I wish you luck Joe & Andi.
Keep us posted.
Patty