The Tropical Fruit Forum

A number of seedlings and grafted specimens as they show leaves preparing to abscise for winter.

A seedling of either Meyer lemon, or Moro blood orange showing good tolerance to this point. No expectations of winter survival.



Ichangquat 6-7-2 seedling showing shoot damage - not deciduous (not expected to be).



TaiTri seedling not showing much damage, partially deciduous at this point.



5* Citrumelo showing minor tip damage, not deciduous at this point.



Segentrange # 58 monofoliate, not deciduous, showing a bit of tip damage (off photo). Original plant (in soil).



Segentrange #21 deciduous, showing little damage. On Poncirus rootstock.



Segentrange #001 deciduous (not last year), no damage. On Poncirus rootstock.



Segentrange # 010 deciduous, no damage. On Poncirus rootstock.



Segentrange # 011 deciduous, no damage, possibly
the hardiest specimen. On Poncirus rootstock.

Swingle citrumelo has 5-10% zygotic seedlings vs 15% for C-35 citrange. Ilya's seeds may have higher percentages and better cold hardy genetics.

Mikkel, have you looked into ordering seeds internationally? Shipping costs would be higher and certification documents would be an additional cost. EU restrictions might make it impossible, though.

Florida Citrus grower reports having reversed the effects of HLB by improving soil health utilizing cover crops. http://citrusindustry.net/2019/11/18/cover-crops-bring-hlb-recovery/.

Here a few citrange and citrumelo zygotic seedling percentages.


Citrus Genetics, Breeding and Biotechnology
edited by Iqrar A. Khan

 Page 144, Table 5.1 gives a list of rootstock zygotic percentages including citrumelos and citranges. A search for book preview gave a number of percentages.

Off the top of my head from other sources: C-35 citrange 15% zygotic, Benton citrange  0 % zygotic, Carrizo/Troyer citrange +/- 1% zygotic, C-32 citrange +/- 10% zygotic. Sanford,Yuma, and Phelps citranges have high percentages of zygotic seedlings. Sacaton citrumelo has fairly high percentages also.

New growth, taken from the base of the tree next spring , allowed to become semi-hard, has potential to root . The basic rule is the more tender the cutting, the easier to root, but also more likely to desiccate. Desiccated cuttings quickly lose the ability to root. So it's a bit of a balancing act between too hardened and lowered rooting ability, and too tender and susceptible to desiccation. Timing is extremely important when rooting cuttings. Senescence of the parent plant is also very important, which can be partially overcome by taking cuttings from recent growth close to the bottom of the plant.

These rules are less important with easy to root species and critical on hard to root species.   

In preparation for winter, the open ground planted trees, as well as the potted trees have been enclosed in a cold frame shelter. This may not be needed in an average winter, but it provides a means for emergency protection if a 50 year Arctic cold event should occur. The very lowest temperature seen in this area in my lifetime was -24 deg F (-31.1 C) in January 1994. Such a temperature would wipe out all the pots and destroy all the other plants, at least to ground level.

This structure was hastily constructed as  we experienced a low temperature of 18 degrees (-7.77 C) earlier this week. The original plan was to cover in early December, but plans were changed due to weather forecasts. The plants easily coped with the 18 degrees. The plan is to protect the stems in order to  get flowering and fruiting in a few years.

There are no intentions of heating the structure, but in the event of temperatures lower than -10 deg F.(-23.3 C) it would be an option.

A number of years ago I did woody ornamental rooting in a heated sand bed within a shadehouse. My favorite rooting formula was a liquid that was used a full strength for hard to root cuttings and diluted for easier to root cuttings. The brand is Dip 'N Grow Liquid Rooting Hormone. By storing the liquid concentrate in a freezer, it kept it's potency for years. Once diluted, the solution was used and left over solution was discarded.

Southeastern PA in the US doesn't see much Poncirus damage in the spring. Prunus cultivars often suffer from freeze damage at time of bloom. Last year citranges began growth in the very beginning of May with no new damage at that point. The northern US is entering a period of unusually cold weather at present and I expect all late growth on both Poncirus as well as Poncirus hybrids to be damaged, or destroyed. Our fall was quite moderate until recently. The forecast low temperature for next week is 16 degrees F (-8.8 C). This is no problem in 6-8 weeks, but is a bit harsh this early in the season.

Great photos, do you have any photos of cut fruit? The fruit does look distinct from Poncirus. How does this tree's hardiness compare to Poncirus? I assume Poncirus has no hardiness issues in your location.

 I once transplanted a mature Poncirus tree with very pronounced nipples on the fruit. The stem end was also elongated a bit, giving a somewhat lemon-like appearance.  The tree trunk was 10 cm in diameter and did not survive transplantation. It would have been wiser to transplant a few of the small seedlings growing under the tree, or save some of the fruits.

As mentioned, the rootstock needs to be of adequate diameter to physically accommodate the bud. A properly fitted bud is important for maintaining good contact between cambial tissues. Freely slipping bark is paramount for successful bud grafting. Forcefully peeled dry adhering bark will not provide the required moisture to the bud and it will fail due to desiccation.

Citrus budding becomes successful if a few basic rules are followed:
1. Budding is best done when the stems are actively growing and are increasing in diameter. It is this active cambial tissue growth that allows the bud to be accepted and incorporated as part of the healing tissue. Failed buds are often overgrown by and "swallowed" by the rapidly expanding bark. 

The temperatures need to be conducive to rapid growth. Excessively high temperatures will stress the plant, but are less injurious with adequate moisture. Low temperatures will retard the completion of the healing process, excessively low temperatures will stop the process.

Failures can be caused by
1: poor mechanical fitting of the bud and rootstock.
2: poor timing of correct rootstock growing phase.
3: out of season budding.
4. immature buds , or "blind" buds, being a node with a leaf, but without a viable bud. In this case the budded tissue heals properly, but fails to push, due to the absence of an actual bud.

If you can get access to bulk wood chips and permission to grade them using 6mm screen, you should be able to create your own. If you're near a farming community, a hammermill feed grinder could quickly process a large quantity of uniformly sized chips.

Impressive, your friend has achieved his " Green Thumb" certification.