Hello.
I was wondering something about the citrus roots "working temperature".
inside another topic I read that citrus roots actually don't work below 55°F
I guess in subtropical and warm temperate climate this limit temperature isn't often reached?
then if the soil is warm and if a cold snap occurs, the damage from freeze will be larger, right?

but for cool temperate climate, this soil temperature is easily reached before the cold, then is it a better thing for hardiness? are the plant fully dormant when soil is cold? so their cold hardiness is better?

another question.
We know that trifoliate orange slightly increase tree hardiness.
but trifoliate orange comes from temperate climate? so its roots working temperature maybe lower than other citrus species?
then how can the hardiness be increased by this rootstock? how does it work?

thanks.
Sam

As I understand it, the Poncirus Trifoliate is a deciduous Citrus species/ relative, that goes into winter dormancy. Any Citrus cultivars budded onto Poncirus, also shut down over winter, to a greater level than they would otherwise on their own roots, or other rootstocks. This gives them greater cold tolerance and delays their spring flush, which is less likely to be hit by a freeze, than more active trees.

arashi wrote........" guess in subtropical and warm temperate climate this limit temperature isn't often reached".............

In subtropic regions that commercially produce citrus, the soil temperature does not reach 55F, so this would not be a problem. A citrus tree gradually begins to accumulate cold hardiness (CH), as the temperatures begin to drop in the fall months. For trees on hardy root stocks, such as trifoliate, temperatures that begin to induce cold hardiness are relatively high: 70° F day/50° F night for about two weeks before a freeze.

The least cold-tolerant rootstocks don't become cold tolerant until temperatures reach 45° F day/26° F night. For citrus tree the scion has much more to do with the trees CH, than does the root stock.

In areas where the winter temperatures are cold enough to reduce the soil temperature below 55F at 3 to 4 inches beneath the surface, I doubt that a citrus tree would not survive growing outside, except in the case of Poncirus varieties, which become deciduous. - Millet (1,143-)

Thanks
But here, Soil temperature goes
as low as 42°F by January at 10 inch.
and citrus can hold their leaves on Poncirus trifoliata.

arashi says " and Citrus can hold their leaves on Poncirus " . I'm not sure I get your meaning, but the scions budded on to Poncirus don't become deciduous too.

thanks for answering pagnr.

As Millet said:

"In areas where the winter temperatures are cold enough to reduce the soil temperature below 55F at 3 to 4 inches beneath the surface, I doubt that a citrus tree would not survive growing outside, except in the case of Poncirus varieties, which become deciduous"

I understood that only Poncirus can thrive planted into
soil that become as cold as 55F matbe I'm wrong


I answered that here, my evergreen (satsuma, sour oranges)
citrus trees grafted on Poncirus trifoliata
survive, keeping their green leaves over winter.

So the low soil temperature doesn't seem to affect
the water input by the roots.


I can grow more citrus than only deciduous Poncirus,
even in cold soil.


I was wondering until what temperature Poncirus roots
can supply leaves? until soil freeze?

thanks