Herman, what climate zone are you in again? Tremendous undertaking. You single highhandedly may advance cold hardy Citrus significantly with these steps. please keep us updated.

I agree, your dedication is very inspiring. Keep the updates coming. The monofoliate specimen is like winning the lottery.

I'm in Zone 6b approximately midway between Philadelphia and Harrisburg,. PA. Also 45 miles north of the Chesapeake Bay.

At this point my project has a long way to go before any substantive results will be evident. That is to say that although the screening process has identified a number of selections with considerable hardiness, what remains to be seen is what fruit characteristics these plants will display.

There is a possibility of there being a tree with good colored fruit, that could be used for aesthetic purposes, despite substandard fruit quality. Another consideration is the fact that an initial cultivar may have the bar set quite low, due to there not being any completion at present. Such a cultivar could serve as a parent on the path to developing more advanced selections. At that point, the original cultivars would likely become obsolete.

Although it's tempting to hope for rapid advances in a short period, it's probably more realistic to view it as a matter of incremental steps toward an ultimate goal.

An example of potential resources that haven't been fully exploited is the discovery of Poncirus selections that lack most of the waxy bitter resin found in Poncirus. Hybrids made with such a Poncirus parent should accelerate the development of hybrids with improved flavor. Both Eastern and Western European breeders have such a section known as Poncirus+ available to them.

In regards to developing a hardy selection with ornamental fruit, incorporating a strong Citrus fragrance during bloom would be very desirable. Despite having repeatedly read about the fragrance of Poncirus flowers, I and a number of others fail to detect such a fragrance. My suspicion is that some writers base their reviews on second, or third hand material, but haven't actually encountered the scent personally. I rather doubt it, but perhaps there is a faint scent present in a few clones.

We have to stick our noses in PT flowers for any real scent. M2C

I agree with your methodology and I too would be happy to grow a larger fruiting Poncirus.

I grow one Poncirus and the oil taste is not dreadful. I’m curious how awful they can taste. Here’s my fruit.

https://youtu.be/5P5E-YjChTU

Some Poncirus enthusiasts suggest more heat during the growing season, as well as waiting until maximum ripeness will improve the taste. I believe continued exposure to the flavor may allow for increased tolerance to the taste ( or increased revulsion) ! Some persons chill the juice in a refrigerator overnight, allowing some of the various liquids to settle out in an effort to discard the worst flavors.

As youngsters, my nephews diluted the juice and pronounced the drink as acceptable. There was likely an element of novelty involved in the process.

Impressive to say the least. I think your rootstock might end up being more important that how good the quality of the fruit. What about taking some of the hardiest rootstock and putting on the standard kumquat, owari, and duncan that can be found on old homesites? I say Duncan because they always seem to thrive on neglect. We have one duncan grapefruit in zone 8 b in hammon LA that is probably 60 years old on a family home site that tatstes amazing if I can ever get out there. I don't know how many freezes its seen in that time but quite a few.

Being located in zone 6b - 60 miles west of Philadelphia, PA rules out grafting tender Citrus onto these trees in my area. I plan to trial a few of these plants 200 miles south of here in southern Maryland, but Kumquats, Satsumas, etc. won't stand a chance. I feel the coastal Carolinas would be the northern edge for edible Citrus using present cultivars.

One potential use might be use as rootstock for Poncirus graft - incompatible lemons at the northern end of the range for lemons. They may offer near Poncirus hardiness coupled with graft - compatibility.

Here's a #011 Segentrange grafted on Poncirus showing leaf color change in preparation for leaf drop. This is one of the hardiest seedlings. The clones grafted on Poncirus display more o this type of color change and are likely a bit hardier than the original tree scion donor.

I find Citrus easy to graft and #011 grafts on Poncirus take very well. Except for the outdoor test grafts on Poncirus, the remainder are in an unheated cold frame for the winter. This won't provide much heat, but will protect from the wind. This will be necessary as much of the stock is in pots.

The cold frame is clad in white overwintering plastic to minimize daytime solar gain.

Let us know how they fair.

Following our extremely mild winter, all plants are in great condition. Some of the F2 hybrids have emerging buds, while others remain dormant. This should set the stage for attaining some height this growing season.

Well, an update:

The Satsuma did not survive inside its cold frame last winter. (But that winter got very cold and had over a foot of snow)

The Bloomsweet and Ichang lemon seem to have survived fine outside in containers this winter. Their leaves are still fairly green.

I also have a little Ichang papeda planted in the ground that made it through this winter. Its leaves do not look really good, have turned a yellow-green color, but I am pretty sure it will survive.

A Changsha mandarin planted on the warm south-facing side, in a sort of protected spot, appears to have made it through this winter well, leaves don't look too unhealthy of a color.

March 28, 2020

Three of my C-35 hardy segregating selections developed deep purple coloration on the leaves during the winter. It appears to be a cold temperature response. None of these trees show any damage this winter. I'm curious if the Ruby blood orange ancestry contributed to this color development, as cold nights reportedly enhance the development of blood orange fruit pigmentation.

Other selections developed a yellow base leaf color, as well as some with a very deep green leaf color.

Great work

After removing a number of selections from the original test plot in the spring of 2019, I neglected the plot until this spring. Following a very mid winter I'm surprised at the abundance of plants that grew from low positions/roots that are essentially unscathed this spring. There are hundreds of such plants. I don't consider them to be reliably hardy to zone 6b, more likely 7b.

I've included a photo of such a cluster of plants, as well as a photo of an F2 plant grafted on Poncirus and left out of doors.

C-35 derived descendants surviving 2 winters unprotected out of doors.

One of several Conestoga citranges breaking buds high grafted onto Poncirus. Unprotected outdoors with no winter injury.

Thanks for the update.

Hi Herman Zimmerman

I read about your experience with citrus in zone 6b and admit that it is great.

From a large quantity of citrus seeds, did you select 69 frost-resistant plants?

What is new in your selection at the moment?

At present, there are about 20-25 recent grafts on outdoor Poncirus rootstock for trial during the upcoming winter. Additionally, there are nearly 500 recent grafts on potted Poncirus seedlings.

F2 citrange top grafted on Poncirus. No damage during the past winter. This selection, as well as several others, although vigorous, has small trifoliate leaves. The leaves are actually a bit smaller than Poncirus leaves.

The tallest original survivor is 7' high. Only 2 of the trees appear to be getting a bit closer to flowering.

There are a few hundred less hardy survivors in the original trial plot. Our past winter was very mild and they didn't freeze back, however, I don't expect that group to thrive after a normal winter.

Outdoor survivors following a very mild winter (+10 deg. F).

Monofoliate F2 citrange #058, new growth has a pleasant scent when bruised.

A few of nearly 500 recent grafts on Poncirus rootstock.

Great work! I'm planning to trial some crosses between my US-852 citrandarin and meiwa kumquat. I was hoping to get your advice/opinions given your knowledge and experience. I'm hoping to incorporate the sweetness of the meiwa, particularly the peel, into a moderately hardy seedling. I suppose I'll be prioritizing good flavor and working toward something that can thrive in an unheated greenhouse in 7a climate.

The larger number of seeds/seedlings you are able to begin with in your trial, the greater the pool of trees there will be to select from. Although large lots of seedlings are initially easy to manage, there needs to be a rigorous screening process of selection and elimination in the fairly early stages to keep the population size manageable. In my case frigid temperatures served the purpose. Eliminating useless nucellar seedlings is important, so you can concentrate on the zygotic individuals. I have discovered 3-4 seedlings I suspect of being nucellar seedlings that survived by virtue of root grafting onto adjacent hardy seedlings. I will watch these very carefully this winter and eliminate them if the are less hardy.

Fortunately Kumquats have a short juvenile period, which may get you to the fruit evaluation sooner than my trees. It was hard to watch some of the seedlings I favored succumb to cold temperatures because they lacked the necessary genetics to survive.

Your priorities lean a bit more toward palatability and a bit less toward cold hardiness. However, there isn't a huge difference between our climates, your coldest winters will likely still be a bit colder than our warmest. By virtue of growing within an enclosure you have the option of providing emergency heat in polar vortex events.

There is a shift of priorities between very severe selection against tender individuals in the initial survival test, and protecting the survivors to preserve the superior genetic material toward the end of seeing them flower and fruit.

I wish you the best as you proceed in you venture.

but I'm not going to use grafting or kumquat seeds I'm using true lemons

here in zone 6b

and I'm not going to use trifoliate genetics in mine

Thanks Herman, you bring up a good point about elimination. While I'm not going for as extreme cold tolerance as you, it does make sense to weed out seedlings quickly by the process of exposure. By focusing my efforts there, I could reach my end goal faster and trial a lot more specimens vs investing substantial time and resources into seedlings that in the end won't perform at the level expected. Thanks! I can't wait to see your final results!

the more seedlings you have the better chance you have to find at least one that can handle the cold

I'm going to be pushing Eureka lemons to start with

these are my lemon seedlings in clay soil in my flowerpot I'm just beginning like you the variety I have growing I do not know

My 2 tallest trees have node counts of 75 and 100+. The tallest is a bit over 8' tall at 28 months of age.

The second tallest is high grafted on Poncirus and has 75 node count plus a few additional from it's original scion donor tree. This particular tree is 1 year old since grafting, it's scion donor tree is also 28 months old.

The node count contributes towards attaining maturity and flowering/fruiting. These plants have grown so rapidly the another 3-4 years are likely going to be required before flowering.

Here's a picture of a Yuzu seedling that is growing here, in the ground:

It has now just reached about 2 feet high.

It was not covered.

I also have a Dunstan citrumelo and a Bloomsweet that is growing outside in special spot in front of a south-facing wall that are looking good. A Changsha mandarin is also looking good.

This one (close up picture) was grown from a seedling that came from an Ichangquat. But while the seedling was growing (indoors), I saw what looked like two separate bifoliate leaves (though this is mostly monofoliate). So I believe this might have gotten pollinated by a citrumelo.

That would make this a (Ichang papeda x kumquat) x (grapefruit x trifoliate) hybrid.

I planted it outside in the ground in January here. At first it looked like it was doing well, but then (not surprisingly) it eventually defoliated and several of the top little branches suffered die-back. But it has since started growing out again, and looks like it may do well.

It probably just didn't handle the initial shock of sudden temperature change from growing indoors in a warm conditions to going outdoors with constant cold.

Nice looking tree, socal. Much easier on the eyes than the battle scarred plants we often see at the end of winter.

Your tree has ideal branch framework. As a teenager I was employed in a fruit orchard and learned the importance of early and consistent framework training. Much better to make small, quickly healed cuts in the early years, rather than large, mutilating cuts in later years.

I agree because it can screw up the trees balance if not shaped right

it might not make sense to reinvent the wheel she may be pushing citrus to zone 8 but I'm going to an extreme by pushing lemons to zone 6 b Howard Martin

poncirusguy6b452xx is it safe to add a1/2 teaspoon of bleach to my fertilizer in a 32 oz. spray bottle

Update on Winter 2020/2021 survival of various Cold Hardy hybrids and selections:

Flying Dragon graft on "standard" Poncirus. Overwintered in cold frame.

3 year old outdoor surviving segentrange. Never protected in Zone 6b. March photo.

#058 outdoor graft on Poncirus, barely survived, most Citrus- like of my segentranges.

Outdoor 5 star Citrumelo on Poncirus, looked rough during Winter, has recovered.

Outdoor Poncirus plus, supposedly has less off flavors.

Segentrange 011 shows no Winter injury, top grafted on Poncirus.

TaiTri Citradia looked damaged during Winter, recovered quite nicely.

One of the less hardy segentranges is recovering despite Winter damage.

Good work))

And I meant to say thanks for sharing)

Thanks again

Herman, has your Poncirus + flowered yet?

Ian, the Poncirus+ has flowered this Spring for the first time. A few of the fruitlets are still on the tree, hopefully at least one will remain to taste in the Autumn.

Awesome. I'm really curious to see if it is better. Can I get some cuttings from you? I sent you a message on FB.

Any updates Herman?

Conestoga 026 Segentrange fruits and dilute beverage. Upon sweetening the beverage is quite good with a hint of grapefruit flavor. Hardiness is a bit less than Poncirus, but trees grafted on Poncirus did well during the past Winter.

Undiluted 026 juice.

Poncirus Plus fruits. The trees are 3 year old seedlings. The Poncirus off flavors are reduced and the juice can be diluted and sweetened as a beverage.

The beverage flavors are less pleasant than those from Conestoga 026 Segentrange.

5* Citrumelos from 3 year old seedlings. Advanced selections descended from Swingle Citrumelo. This is the only hardy Citrus hybrid I have that has a sweet taste.

Grapefruit taste is evident as well as slight bitterness and acidity. Rather late ripening. Makes a decent drink when diluted.

Wow thats pretty good, fruit from a 3 year old seedling. My citrumelo is years older and hasnt bloomed yet. Not sure what variety mine is, they are supposed to be from seeds of an in ground citrumelo in Winston-Salem, NC, or so I was told.

i appreciate your continued updates to this post. Good luck with your cold hardy citrus endeavours.

Dunstan Citrumelo is often planted in the Carolinas. I have 3 different Citrumelos, of which only one has fruited.. The other 2 are less than a year old.

Herman, thanks for the update. It’s great to see fruit already. How large are the Conestoga 026 Segentrange and Poncirus Plus fruit? They look similar to PT…….or are they larger…….photos can be hard to judge. Great to hear 5* Citrumelo has some sweetness. Fruit ripens around Thanksgiving……but the size is clearly larger than PT…….a nice selection. Getting fruit in 3 years is very fast. I gave my brother who lives in Fairfax, VA a seed grown Citrumelo 12 years ago and it still hasn’t bloomed! Keep the updates coming.

Poncirus Plus fruits are smaller than Poncirus I have on my property, perhaps due to being the first time the trees have fruited.

Conestoga 026 fruits are essentially the same size as Poncirus, but are very round and thin rinded.

5*Citrumelo fruits have been larger than Poncirus fruits with thicker rinds. They also ripen a bit later.