Cold hardy citrus trees

Make sure you keep the seeds moist. Citrus seeds aren't like apple or pear seeds. If they dry out, they will never germinate.
John S
PDX OR

I have grafted a Poncirus trifoliata to Seville sour orange to serve as an inter-stock since Meiwa kumquat can't be grafted onto sour orange

I won’t have any seed until I start harvesting the crop later this month.  The citrumelo cultivar is Dunston.  I have 2 foot high, 1 year old citrumelo and Yuzu seedlings, but I’m not set up for shipping plants.

this years greenhouses will provide shelter for my Fukushu kumquat for its 5 winter planted outside and in ground.  4th winter outside and in ground for my Nw Zealand lemonade on C35 rootstock.  3rd winter outside and in ground for my Valentine pomelo on US897 rootstock.  Last my Meiwa kumquat on kuharske citrange will see its 2 year outside and in ground.

For many years I have been trying to figure out how to make some kind of a greenhouse work.  I know my Meiwa kumquats would love it. I use plexiglass covers for some plants like Thyme and licorice, which don't like our wet, soggy winters and springs.  They die otherwise, from diseases. They like it dry in winter.  We don't get as much cold as in Cincinnati, but we're very wet for a very long time.  Partly I have to figure out where I would store the glass during the rest of the year when we don't need it.  I know that you can get some windows and things cheaply if you go on Craigslist or Restore, for example, but the logistics are important. Getting something together cheaply that can be stored easily is the trick.  Thanks for inspiring us to figure out how to do it.  

John S
PDX OR

I have a small greenhouse I made out of used windows I bought at Habitat for Humanity, it's kept my in ground Satsuma mandarin trees protected for about 7 years or more now.
The greenhouse stays up year-round but many of the windows can be removed or opened for summer use.  When I take them off I just put them beside or in the greenhouse.

So it seems that folks are worried about citrus trees in greenhouses?  This is my concern because I am hoping for a lemon tree in a big pot in the greenhouse I am building. Is supplemental heat the concern? or, is it cold ground that that is the issue?

I have an aquaponics setup that I am installing; I decided that I am going to enclose it with a greenhouse so I do not have to harvest all of the fish (Tilapia) before freezing temps each year.  I have considered heating the water with a solar flat plate or an evacuated tube solar collector and hoping that the ambient heat from the 300 gallons of water in the tank along with the water running through the grow beds and sediment collectors will be enough passively warm the greenhouse enough at night without any additional heat inputs.

Is there a minimum winter temp for citrus trees? Is there a minimum number of winter daylight hours needed for citrus (Lemon)?

This was an interesting thread to peruse.  Thanks

Mark
Frog Hollow Schoolmaster's Homestead
Myersville, Maryland

Mark, Lemon trees are the LEAST cold hardy of citrus trees, you'll need to keep it above 29F at the least.


I have Owari Satsuma mandarins in ground in my greenhouse, but they are hardy to around 22F, so there is wide variance between varieties of citrus.
(The only heat source is two incandescent light bulbs, one near each tree.  They are turned on by a greenhouse thermostat at around 35F.

Edit:  Some info on varieties of cold hardy citrus: https://www.gardeningknowhow.com/edible/fruits/citrus/cold-hardy-citrus-trees.htm

Meyer lemon and ishang lemon are more tolerant of cold than true lemons.

Due to predicted lows of 22 degrees F, I harvested all of my Yuzu crop and most of my citrumelo crop (left some fruit deep in the tree’s interior to be picked later).  Result; two wheelbarrow loads of citrumelos and a bucket each of Yuzu and citranges.  Used one of those long handled cut and hold pruners to pick the fruit, making harvesting fruit from the thorny tree a much less painful process than if I tried to hand pick the fruit.

If your citrus trees have fresh growth they need to stay frost free and above 32F and the fruit is destroyed below 28F.  My trees seem to do fine with 8 houres of daylight rain or shine.  

New additions to my Fukushu kumquat collection grafted late summer 2020.  the 2 trees started growing 1 month apart.

I have taken my indoor citrus trees outside for acclimating for summer sunlight.  It is probable that they will have to come in for cold weather.

I've had a look through the posts on here and can't find anyone posting from the U.K. - most appear to be from the U.S.A. Why is that ?

Folk are growing avocados in the U.K., so why little interest here in Citrus ?

Most of the U.K. is 8A/8B, on the USDA plant hardiness scale (though the full range is 7a to 10), so at least some cold-hardy Citrus would be well adapted to many areas within the U.K. There are several examples of various Citrus growing outdoors, within the London area.

Hi Mike,
It's mainly that there are fewer of us from the UK that are active on Permies.
I have a 'unknown citrus' in my polytunnel. Seed grown by a neighbour. I planted it out, but don't give it enough protection so it dies back most years (we don't  get colder than about -10 deg C though usually) and I don't get fruit. I've had it about three or four years now. It's most likely a lemon or orange I guess, nice scented leaves and slightly spiny. I thought I'd lost it last year, but it grew back from the roots again....We've not had a hard frost this year so it is still green. I should get out and put something round it in case we do turn cold in late winter....
I have seen lemons outside in the South of England - at hridayabija: seed of the heart Forest Garden in East Devon, Sagara had fruiting trees outside with rock walls to the north to give a sheltered microclimate. I don't think he gave them extra protection.....

Examples of Citrus growing outdoors, within the London (U.K.) area: http://homecitrusgrowers.uk/citrusplaces/londonoutdoorcitrus.html

Nancy Reading wrote:Hi Mike,
I have a 'unknown citrus' in my polytunnel. Seed grown by a neighbour. I planted it out, but don't give it enough protection so it dies back most years (we don't  get colder than about -10 deg C though usually) and I don't get fruit. I've had it about three or four years now. It's most likely a lemon or orange I guess, nice scented leaves and slightly spiny. I thought I'd lost it last year, but it grew back from the roots again....We've not had a hard frost this year so it is still green. I should get out and put something round it in case we do turn cold in late winter....

You seem to be at around 57.4° N (Isle of Skye) - though warmed by the Gulf Stream I was surprised when you mentioned it could dip to minus 10 C, but then I guess how cold it is also depends which way the wind is blowing from, like down here where I am. My goodness, your Citrus plant is a real survivor, and deserves you to go out and give it a bit of TLC right away!  Once it's got bigger, though it may well be a bit more cold-hardy - some of these subtropicals get better with age.  To protect young avocado seedlings from frost (when small), I'd just invert a 100 Litre black plastic refuse bin over the plant for the night, weighed down with some bricks so it wouldn't get carried away by gales, remembering to remove it of course when daylight returned and temps had rewarmed to 0 C or above - maybe you could do the same with your Citrus in the polytunnel ...

Hi Mike,
Yes I'm up on Skye. Normally we don't get below -5 deg C but every few yeasr we'll get a colder spell. This year we've not had a hard frost yet - going through a typical wet and windy spell at the moment, but it is generally between 5 degC and 10 degC. Cold, damp and dark...still it's light at 5pm these days and soon be spring....
Good idea with the upturned bucket. I may have an old waterbutt (US = barrel) somewhere. My polytunnel is in shreds just now, although the citrus is in the surviving end. What I normally do is wrap the plant in some old windbreak fabric and just leave it till it gets warmer, but I am a bit worried about causing rot..
It would be quite nice to get fruit or even just flowers! so I should take more care of it really.

This question is a bit of a longshot!
Does anyone know of a supplier in the U.K. that sells Owari Satsuma grafted onto trifoliate orange [Poncirus trifoliata] rootstock, or onto other cold-hardy rootstock ?

I already tried the Citrus Centre in Sussex, but they don't use Poncirus. Previous studies have clearly shown this rootstock to markedly increase the frost-resistance/tolerance of the Satsuma trees grafted onto them, when they're more mature, apparently down to minus 8°C.

Many thanks for any leads ...

Mike Guye
I was Lucky.  Someone gave me a bunch  of  Flying Dragon seeds and I was able to grow my own FD rootstock.  It is almost impossible to find any citrus grafted to PT or FD here in the US.  My suggestion is to look for a fruit from PT or FD.  There are no other rootstock that adds cold hardiness similar to these 2.  I am using Seville sour orange for my rootstocks for non kumquat citrus and FD for kumquats.  I get temperatures as low as -23C and can't plant outside with out a 4 layer glass shelter and a heat source.  Kumquats are best on PT/FD which can't be found in the USA.  Best of luck/skill in your search to you.

Steven Rodenberg wrote:Mike Guye
I was Lucky.  Someone gave me a bunch  of  Flying Dragon seeds and I was able to grow my own FD rootstock.  It is almost impossible to find any citrus grafted to PT or FD here in the US.  My suggestion is to look for a fruit from PT or FD.  There are no other rootstock that adds cold hardiness similar to these 2.  I am using Seville sour orange for my rootstocks for non kumquat citrus and FD for kumquats.  I get temperatures as low as -23C and can't plant outside with out a 4 layer glass shelter and a heat source.  Kumquats are best on PT/FD which can't be found in the USA.  Best of luck/skill in your search to you.

Well done Steven - so glad you were able to succeed with that !!  Was the grafting fairly straightforward, I mean as easy/difficult as any other plant material ?
You know what, maybe eventually the only solution is to buy a P. trifoliata cv. Flying Dragon plant, wait for it to provide me with fruit/seeds, germinate them for rootstocks, then graft buds from a purchased Satsuma plant onto it. Seems a bit of a long haul ...  but, from what you say, may it's the only solution!

If you can read French and you're interested in growing cold-hardy citrus, then I highly recommend you purchasing the following book: "Agrumes resistant au Froid a cultiver en plein terre" (= Cold Hardy Citrus to Grow Outdoors). Authors Olivier Biggio & Bertrand Londeix, published by Ulmer, Price 16.9 Euros.

I've just bought my copy and read it from cover to cover - fantastic book that breathes optimism into the prospect of growing Citrus outdoors in parts of Europe where they wouldn't normally be grown. If you're in the U.K., post and packing will be another 15 Euros approx.

Below are some scans of the book cover and the contents page.

I harvested 74 New Zealand lemons and 1 valentine pomelo this winter then both trees died.  Don't know why.  My seed grown Fukushu Kumquat and seed grown Meiwa kumquat survived and look good.  I have another seed grown Fukushu kumquat that will go in where the lemon grew and a seed grown Meiwa that will go in where the valentine pomelo grew.
As far as grafting mentioned above it is just routine grafting.

I had a New Zealand lemonade, Valentine Pomelo, and a Seville sour orange all of which died.  I also had 8 container citrus with the 3 in ground and all of them survived.