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When/How to chill specialty citrus tree for blooming?

Posted by darlox 6a (My Page) on
Sun, Nov 28, 10 at 12:26

Hi all,

So this is my first winter with some more exotic citrus (yuzu, citron, along with the usual lemon/lime), and also my first winter with a greenhouse. I sort of went a little nuts in filling it, so as a result, my citrus is sharing the space with some plants that require the temp to be kept above about 60 degrees all winter.

Turns out, this may have created a problem with the yuzu in particular, in that everything I've been able to determine (including a separate post here) indicates that it needs a significant number of chill hours annually in order to blossom & fruit.

Presently, the tree is LOVING the greenhouse, in terms of growth. In the last month alone it has put on as much as 6" of new growth from several new shoots (top growth - not suckers or anything else problematic). It likes the GH better than it liked being outside all summer, in fact.

My question: What is the best way to get this tree the chill hours it needs, and when is the best time to do it -- right now, or in the spring? Having never had to do this before, my biggest fear is shocking the tree to an untimely death in the harsh Ohio winter. I don't have any indoor spaces I can realistically move it to, other than un-lit garage spaces.

One local garden center just suggested hauling it out into a semi-sheltered area sometime around April, and hoping that we don't have extended hard-freezes before spring arrives in earnest. That seems a slapdash way of handling this, and the local growers aren't exactly citrus-experts anyhow!

Any advice or tales of similar success would be helpful! Thanks in advance.

Follow-Up Postings:

RE: When/How to chill specialty citrus tree for blooming?

How many hours are you talking about? Though I am not familiar with this particular citrus, I can't imagine any of the species requiring 'significant' chilling hours. Educate me!

RE: When/How to chill specialty citrus tree for blooming?

Heh... well, this may well be the blind leading the blind here. My references are all second-hand as well, so I have NO independent confirmation as to whether this is correct for a yuzu.

What I'm told, however, is that yuzu is hardy down to ~8F, and the areas of Japan and China where it's commercially grown receive about 200-500 "chilling hours" (< 45F / 7C) annually on average. So the running theory is that if my yuzu isn't blooming, it should be chilled in that range before being brought back to growing conditions. I've not been able to find any detail on the tree's actual needs, so we're all working on the premise that if it's not behaving normally, first, replicate the conditions where it's native.

It's possible that this isn't necessary at all, and my tree isn't blossoming for other reasons! I'm a complete greenhorn when it comes to the specialty citrus, so my basic premise here might be incorrect.

RE: When/How to chill specialty citrus tree for blooming?

I don't think that this plant has any special chilling requirement, such as those for deciduous fruit and nut trees. However, cooler winter temperatures can assist the citrus buds into differentiating from foliage tissue to flower tissue.

Cool temperatures don't need to meet the criteria for chilling hours, either. That would mean < 45F, as you have noted. Your greenhouse temperatures should be cool enough for you to see plenty of flower buds. Does your greenhouse have a cool spot? Try for ~60F.

This is garnered from bits and pieces of information I've been able to stumble across. Trust me, if chilling hours were necessary, we'd all be able to pull up those numbers swiftly.

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