This sort of reflects what I’m seeing too.
The US (and older) varieties are more productive but smaller and later.
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Since this is a question about the U.S. south thought I would share my Texas experience. Live near DFW in TX and have grown Nazametz, Cooledge and Mammoth, and recently added three new NZ cultivars released with no info on those. Summers here are very hot, winters are mild but get in the range of 600-800 chill hours depending on the winter. While our winters are mild and have below freezing temps we get maybe a total of 5 days of very cold weather (for us) sort of spread around winter. How cold it can get for a day or two here varies a LOT from winter to winter. 25F may be the coldest a lot of the time, but every four to five years we get a lot colder. in ‘21 we hit 0F one night, and maybe 2-4F the next night, daytime was about 8-10F one day and a bit higher the next in the low teens. The lowest temps were maintained for only a few hours each night. Then this winter in ‘26 a few weeks ago we had a brief sharp cold spike down to 5F one night with it maintaining that temperature for an hour or two maybe low to mid teens for a day, maybe two during the day time. I need to tell you that information to give you an idea of what the problems are in Texas.
So what happened with the cold. First it seems some varieties are a bit more cold hardy than others as I will note. That ‘21 weather I mentioned above did a lot of damage and this was even with me putting a huge tarp over the plants to provide a bit of insulation. Mammoth was completely killed and did not grow back from the ground. Cooledge was killed to the ground but resprouted from the roots. a few Nazemetz had a few thick above ground branches survive with everything else being top killed, with one of 7 bushes was completely killed. All Nazemtz were top killed or very nearly so except as noted. Those that were completely top killed sprouted from the ground except one which died. This was just a few hours of 0-4F weather, followed by highs of 8-10F for a day, tarps over all plants. Mammoth was most sensitive, completely killed.
Now looking over my plants after a relatively brief spike down to about 5F for an hour or two followed by mid teens in the day and plants were coated in ice with a bit of snow coverage. As far as I can tell my Nazemetz, since grown back, without tarps, only had the smallest outer branches damaged, but came through well. Cooledge has lost about half its leaves and I am not sure if those branches are dead but it is definitely not top killed, but might have a bit more damage from the weather. Don’t have Mammoth any more of course. The ice and a bit of snow probably provided some insulation, how much I don’t know. But they came through better than expected. As best as i can estimate 8-10F is where it starts getting dangerous and more serious damage starts, how much depends on variety. 8F might be too much for Mammoth, but minor damage to Nazemetz for example. Leaf loss occurs around these temperatures, in fact leaf loss happens a bit higher than these temps maybe 10-12F. However leaf loss does not necessarily mean the branch is damaged. I have had leaf loss with miniimal branch damage. So with my recent cold snap I actually need to wait till the trees start growing again to see if it is just leaf loss, or a bit of branch damage too on the outermost branches of Cooledge. Nazemetz does not have nearly as much leaf loss for this event. Maybe the ice was more insulating and protected them, I expected overall more damage. Anyway, depending on variety 10F is kind of the lowest temp they can handle with minimal damage other than leaf loss. A bit more sensitive variety like Mammoth may be 12F, Nazemetz may be 8F, Cooledge at 10F as best guesses where more serious damage starts. Lower than that and the size of the tree, how long it will be that cold, any protection you provide all matter for the tree’s survival. For example in the bad cold spell, the above ground branches that survived might have been because there was quite a bit of leaf litter (from a near by oak) that I think covered the lowest thickest branches. It may have provided the insulation needed for survival, or it was just the branch being thick enough, don’t know.
The extreme summer heat100F as high as 110F on rare occaisons is no big problem as long was there is water. They are drought tolerant but will do better with not letting them dry out too much in drought, and of course you will get better growth if you keep the soil watered at least once or twice a week in a drought. Once established they can handle high heat and even drought to a degree, but as noted better results with some watering. Frosts generally don’t hit till Nov. but we had one Oct. 31 a few years ago which is really early. Most of fruit, but not all, had ripened by then. My ripening order was Mammoth, Nazemetz then Cooledge. The difference in peak fruit ripening differs by about 10 days to 2 weeks I think. Lots of overlap but Mammoth was first and was still producing a lot when Nazemetz started ripening etc. The October 31 frost was enough to damage maybe 1/4 the fruit on Cooledge and the remaining 10% of fruit on Nazemetz to give you an idea of ripening time. Mammoth would be done by Oct. 31.
The heat does not have a negative effect on the fruit. The fruit have been very good on all three of these. The differences in tastes were subtle with Nazemetz and Mammoth being pretty similar, but Mammoth had bigger but not huge fruit. Mammoth also grew in tree form, but Nazemetz tends ot over bear thus result in smaller fruit. Cooledge had decent size fruit and di not typically over bear. Note I hand pollinated between varieties so my pollination was likely excellent, this may contribute to Nazemetz overbearing.
Otherwise, high heat here is no problem. Normal summer dry weather with high heat not much of a problem. Start getting drought and they will survive but not grow as much, fruit may be smaller. So supplemental water maybe weekly during 100F with drought is going to make them happier. Droughts at lower temps probably don’t have quiite as much a need for supplemental water. But I have left my bushes one summer for a month in 100F weather in drought without supplemental water and they survived. They didn’t thrive like that, but were not hurt.
You probably need to heat to ripen the fruit. Not 100F, but cooler temps at some point probably affects fruit quality, can’t comment on that as we never have cooler temps. But the big issue is what is your coldest day or days in the winter and how long does it stay that cold? In the south that is the main factor. If you are hitting 0F every year it is going to be a problem, even if it is for two days. 10”F and above, probably fine but will lose some leaves. 8-10F is kind of the danger zone that might mean some damage to branches, or a lot depending on variety. A big, mature tree can bee killed to the ground with several hours of 0F, I imagine a smaller immature tree is a lot more sensitive and may be killed at 8F or a bit more, but I am guessing. My plants were mature not new.
Hope that helps.
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Which fertilizer do u give the trees?
I’m hoping joining in on this thread is the right thing to do. I skimmed it, but didn’t quite see an answer to my question: I’m trying to decide on a partner plant for Nikita that is in the 8’-12’ high range with good fruit under crowded - hedging - conditions.
I’m growing in Piedmont NC on a north slope where towering loblolly pines are to my south - it makes the north slope even cooler. Yay, i say, natural air conditioning.
Nikita will be closest to the house so i want a smaller plant there. I’m currently looking at Kakariki and Kaiteri (all to be from One Green World) but if there is a better partner to be pollinated by Nikita but remains in the 8’-12’ height with fruit better than Nikita i’d be delighted to consider it. The plants will be crowded, if that matters.
Thanks for your advice while i finish digging out the clay upslope to level the boxes and mine my compost piles to create soil for these trees.
Longer story:
I have a tight location and i’m greedy. I want to optimize for diversity and not fruit production. But i want some fruit. I am squeezing in some new trees near our house to act as a buffer against the heat pump sound and visual clutter of electricity switch boxes. This is some of the warmest & sunniest location left. It’s on the west and a wall comes out about 30’ to the south which traps warm air on sunny days. There’s disruption (berms) up hill to limit cold air rolling down the hill.
There will be two raised beds, 3 x 6 and 4 x 8. At the corner there is a 2’ gap between house and the narrow end of the 3x 6 container. Perpendicular to the 3x6 container away from the house is the 4x8 container – so the 4x8 container is 4 ft from the house. Immediately to the south, on the other side of the walking area is a Chicago Hardy fig. To the southwest is a young Dunstan chestnut (from seed from High Rock Farm in NC) that may eventually make all of this moot.
Nikita (5-6’ high) will go in the 3x6 next to the house. To its west in the same container the dwarf yuzu from one green world (4’-6’ high).
In the 4x8 container the to be determined feijoia and then a Thomasville Citrangequat from Madison citrus (15’-20’, already ordered). I expect if i like yuzu, i’ll be growing from seed for the other remaining sheltered and sunny location.