Very few citrus can be considered cold-hardy. Kumquats and Satsuma mandarins can generally withstand −5 to −10 °C temperatures after they are established, but will need protection for the first few years.

Try this link for more information:

http://www.chestnuthilltreefarm.com/store/c/40-Cold-Hardy-Citrus.aspx

I have grapefruit , calamondin oranges, satsumas , lemons, kumquats , and they all fruit and grow well with winter temps around 18-20 Degrees F at the coldest nights.

Thank you all for the replies I will plant a kumquat and I will try my luck with a lemon but you did not answer my main question which was how to (if it's possible to hybridize two cirus trees )since I want to grow a sunquat and a limequat but where I live no one sells them.

Thank you for ur answers.

Toni

Breeding citrus has traditionally been a very difficult process since seed grown trees take many years to mature to the point of fruiting. Although it looks like there may be a new tool for the professionals https://www.ncbi.nlm.nih.gov/pubmed/26920394

As to citrus you can grow in your climate, I also live along the 8b/9a line and grow mostly Satsumas in ground, however we typically have the issue of all citrus being wiped out during extreme winters every 25-30 years. Covering and adding artificial heat source (christmas lights) on the few coldest days of the year is needed here some years.

Thank u for clearing that up It seems that breeding citrus is something I can't do and about the extreme lows well in my opinion they are nothing a cold frame and a few buckets of water can't solve.

Anyway does anyone know what the citrus tree on the picture is?

It's in our garden for 15+years and it produces like crazy when the fruit is ripe it is yellow in colour and it has very little seeds way too sour and bitter to be eaten on it's own (in my opinion)but juiced its amazing.

When does it ripen?

It ripens in november but it can stay on the tree until spring comes.

I suppose you may already know that the Meyer Lemon gets it's hardiness from being a cross of Lemon with and Orange (Oranges being more hardy). The Lime is the least hardy, though the Bears Lime is safe in Zone 9. Your best bet is to try grafting (if you can get scion material) onto your hardy root stocks.

Oh and your tree may be a form of Pomelo (called Citrumelo), they are pretty hardy and have a very thick skin.

Yeah i know that,scion material is extremely hard to get here.

I'm pretty sure it's not a pomelo since it's skin is thin.

And aren't pomelos tropical?

I guess I mixed it all up.

It's very hard to tell what a citrus is from a photo.

Other indicators, such as cross-section of ripe fruit, degree of seediness, presence or absence of thorns, presence, size or absence of winged petioles, ease of skin peel, crushed leaf fragrance, time of maturity (although that can vary depending on your heat level and climate), etc. can help.

Ok so it does not contain a lot of seeds maybe 3-8 per fruit.

It is not thorny.

The skin is almost impossible to peel.

The leaf fragrance is not strong but it smells bitter.

The fruits will be ready to pick in 2 to 3 weeks.

I will give more detailed photos so you guys can see the leaf size,fruit size etc.

Pumelo?

A Pummelo would not stand a chance in my climate.

the fruit in those pictures is most likely, based on the lack of thorns the leaf shape fruit size, a grape fruit or grape fruit hybrid of some kind.

Oh ok thank you for ur reply that's what I tought but does anyone know what hybrid is it?

It is probably a lemon cross or sour orange. I have one that is red / dark pink on the inside , very juicy and sweet and is most likely a orange cross