Climate

The minimum temperature that American persimmons can generally tolerate — when referring to earlier ripening varieties from a northern strain — is not well known, but it is often said to be zone 5a.  However, there are a few people who have reported no damage after experiencing those between -22F and -31F. If this is fairly consistent, the primary issue with growing persimmons in zone 4 may not necessarily be cold hardiness (at least after a few years of protection), but the length of the grow season and the amount of heat the area receives.  If your area experiences a grow season around 4.5 to 5.5 months long and is capable of accumulating ~2250 Grow Degree Days (GDD) (based on the information provided at weatherspark), then there is a decent chance that part of the crop of an early ripening variety will be able to ripen on the tree before the end of the season (a GDD of at least 2500-2800 would be more ideal).  An area that experiences less GDD but a longer grow season may be suitable as well, such as those seen in the Pacific Northwest.  Alternatively, you should be able to harvest them when they are yellow and have them ripen on the counter.  This tends to work quite well for Asian persimmons, and it seems to generally work for improved American persimmon varieties, too.

Pollination

Asian persimmons are parthenocarpic.  They will produce seedless fruit without the presence of a pollinator.  Some female varieties can also produce male flowers, but it's not necessarily a yearly occurence and it might take awhile longer for them to first appear.  Wild American persimmons are often self-sterile and require a male and a female tree for fruit production (dioecious), but with the exception of a few older varieties, only parthenocarpic selections have been named.

Pests and Diseases

There are currently no significant pests or diseases that harm American persimmons.  Leaf spot is very common, and it can develop quite heavily on some varieties (or in some regions), but it generally does not concern anyone and is largely ignored.

Persimmon Sudden Death Syndrome (SDS), an affliction that causes Asian persimmon trees to die within 2 to 5 years, is the only disease of any significance that affects them in the United States.  It is currently believed to be caused by Xylella fastidiosa,^[1] a bacteria that is primarily known for causing Pierce's disease in grapes.  Xylella fastidiosa is often spread by large leafhopppers called sharpshooters, but the primary vector, the glassy-winged sharpshooter (Homalodisca vitripennis), can only survive in regions with mild winters.  Based on their distribution map, their northern limit should be around hardiness zone 8a.  Sharpshooters were not mentioned for spreading fastidiosa directly to Asian persimmons, but it did imply that the primary source of infection came from grafting Asian persimmon scionwood onto infected, but asymptomatic, American persimmon rootstock.  Furthermore, there may be another pathogen in some American rootstock that can induce decline (rather than sudden death) in Asian persimmons,^[2] but I have only seen mention of this in one country outside of the United States.

Canker is either uncommon or non-existent on American and Asian persimmons in the United States, but it has been reported in other countries of various climates, such as Japan, Brazil, Spain, New Zealand, and South Africa.^[3][4] The significance of the pathogens that have been isolated from the canker is hard to determine due to the small number of studies on the issue, but the lack of concern over the past few decades implies it is generally quite rare or easy to control.  However, there was one thing that stuck out in a study conducted in South Africa.  Lesions were generally longer on Asian persimmon trees that were grafted to American persimmon rootstock than those grafted to Asian persimmon rootstock.^[4]

Persimmon anthracnose, caused by the fungi Colletotrichum horii (previously thought to be Colletotrichum gloeosporioides), can damage young twigs, leaves, and fruit.^[5] It is uncommon or non-existent in the United States, as well as Europe, and the only regions where it seems to be a problem (Korea, Japan, southeastern half of China, and the San Paulo area in Brazil) tend to receive an incredible amount of rainfall at some point during the grow season.  The rate of infection within these countries "might" be increasing, but for many decades, there seemed to be a lack of concern over the disease.  However, poor practices, such as using slightly susceptible yet infected rootstock from wild persimmon trees, or planting near forests with high disease pressure, has devastated nurseries and orchards in the past.^[5] Most Asian persimmon varieties appear to be fairly susceptible, but some show resistance, such as Nishimura-wase (Coffee Cake).  Furthermore, there is at least one Chinese variety from the persimmon species Diospyros glaucifolia that is considered to be immune.  Overall, not much effort has been placed into the discovery of resistance varieties.^[5]

Circular leaf spot (Mycosphaerella nawae) is a fairly new and serious foliar disease that has recently been spotted in China, Korea, Japan, and Spain.  Infected trees may defoliate early, which can lead to crop failure.  While there are a number of foliar diseases that can affect persimmon trees, M. nawae may be the most severe.

Moisture from dew and a high relative humidity can be enough to progress maturation and encourage spore dispersal.  However, dispersal is far greater when the fungus is exposed to rainfall.^[6][7] In the dry climate of east-central Spain, flood irrigation is a very common practice within persimmon orchards.^[7] This may be why M. nawae is capable of thriving there.

M. nawae has a long incubation period on infected leaves, so fungicides need to be used in spring, long before symptoms appear.^[8] Roughly 4 months after full bloom, symptoms are still fairly mild, but defoliation can become significant 2 to 4 weeks after this point.^[8] Removing infected leaf litter and using drip irrigation are practices that should reduce symptoms, but no studies on the effectiveness of this have been done.

Nutrition

Ascorbic acid (vitamin C) can vary significantly within Asian persimmons, and it depends on multiple factors, such as the variety, their environment, and the stage of which they are harvested.^[9][10] In a multi-study review from 2011, the mean value of ascorbic acid in Asian persimmons was 47mg/100g FW (fresh weight).^[11] This, however, included one fairly old, often cited study with many "fully mature" varieties that had rather high values in comparison to nearly all others (between 35mg/100g to 218mg/100g, with most residing in the upper half of this range).^[12] In more recent studies, the ascorbic acid content resided between 9mg to 87mg/100g, most of which were between 15mg to 43mg/100g.^{[9][13][14][15]}

There seems to be very few studies that attempt to determine the ascorbic acid content of American persimmons, and the only one I have access to happens to be the one that gave the majority of the Asian persimmons tested an unusually high amount.  The one American persimmon they analyzed was determined to have a total vitamin C content of 86g/100g FW.^[12]

Persimmons generally have a water content of ~80%,^[16][9][15] which is lower in comparison to the average, commonly available fruit (85-90%).  A higher amount of sugar and pectin partially make up the difference.^[14][15] Furthermore, they have a pH value between 5 and 6,^[9] which is very high in comparison to most other fruit (less than 4).  This is true even while they are green, but rather than being very acidic, unripe persimmons are very astringent, regardless of which category they reside in.

Astringency

Astringency is the dry, puckering feeling in the mouth, which is generally caused by soluble tannins binding to proteins.  Soluble tannins are present in large amounts in persimmons, but as the fruit ripens, they are converted into non-astringent, insoluble tannins.  Some Asian persimmon varieties will lose their astringency around the time they become fully colored, although it may depend on whether they were pollinated or not and how well they were pollinated.  Overall, Asian persimmons can be distributed between four different categories.

1) Pollination-Constant Astringent (PCA): the typical astringent persimmon (this currently consists of all American and hybrid persimmons as well).
2) Pollination-Constant Non-Astringent (PCNA): the typical non-astringent persimmon.
3) Pollination-Variant Astringent (PVA): an astringent persimmon that lacks flavor if it has not been pollinated.
4) Pollination-Variant Non-Astringent (PVNA): an astringent persimmon that lacks flavor if it has not been pollinated.  If it has been pollinated, the flavor improves and it may ripen in a way that qualifies it as a non-astringent persimmon.  

Persimmons are considered to be edible in Japan when the soluble tannin content drops below 0.1% of their fresh weight.^[17] When astringent persimmons become fully colored, it often resides between 0.5 to 1%.^[18] It will not drop down to an acceptable level until they start becoming very soft, almost like a water balloon.  As for non-astringent persimmons (PCNA), their soluble tannin content is roughly 0.5% in the green stage, ~0.2% in the stage their color rapidly changes, and ~0.1% or lower when they are fully colored.^[18]

PCNA and pollinated PVNA (non-astringent and potentially non-astringent) persimmons lose their astringency in different ways.  Soluble tannins in PCNA are primarily diluted as the fruit develops.  This is possible because their tannins have a smaller cell size and their production ceases at a much earlier stage than in astringent varieties.  In pollinated PVNA persimmons, the soluble tannins coagulate and form insoluble tannins by reacting with acetaldehyde produced by the seeds.^[19] Consequently, pollinated PVNA persimmons with a higher number of seeds will lose their astringency quicker than those with a low number.^[19] A similar event happens in pollinated PVA persimmons, but to a much lesser degree, thus causing them to remain astringent for a longer period of time.

Diospyrobezoar

A diospyrobezoar is an indigestible mass in the digestive tract caused by shibuol, a soluble tannin largely present in persimmons that haven't ripened enough to lose their astringency.^[20][21] In the presence of dilute stomach acid, shibuol coagulates into a cellulose protein structure.^[21] Soluble tannins in persimmons are found in higher concentrations near the skin and calyx.

Diospyrobezoars are quite rare, and roughly 80%+ of those who do get them have impaired gastric motility due to some form of surgery.^[20][21] The majority of the others also had a disorder that can impair gastric motility, such as diabetes mellitus or hypothyroidism.  Additionally, improper chewing may have helped lead to the formation of a diospyrobezoar in some people.^[21]

In one study of 103 patients who were believed to have had a diospyrobezoar, symptoms developed 1 day to several weeks after consuming persimmons.^[20] Laparoscopy is generally the most invasive procedure required for their removal, since larger incisions are rarely needed.^[22] Endoscopic procedures are more common and are often done in combination with carbonated liquid or enzymes to help soften regular bezoars,^[22] but it's generally not attempted with diospyrobezoars due to their harder consistency.

Examples of the kind of persimmon consumption that have lead to the formation of a diospyrobezoar are hard to come by, and it will certainly be different for each individual.  Regardless, a few examples are better than none.  The following three patients had some disorder or gastric surgery that may have caused impaired gastric motility.

1) a 66 year old male said he recently consumed 12 persimmons, but it did not go into further detail.^[21]
2) a 51 year old woman mentioned she ate 2 or 3 persimmons per week over the past 6 months.^[23]
3) a 70 year old Japanese man with no symptoms was discovered to have a diospyrobezoar during an annual screening.  He claimed to have had 2-3 persimmons each day for 3-4 months during the previous fall and winter season.^[22]

In one case involving a patient that may not have had impaired gastric motility, a 27 year old male vegan developed symptoms after switching to a more seasonal food diet for one month that consisted of over 10 persimmons per day.^[24]

Overall, people who have impaired gastric motility, or some other issue that may lead to the formation of a diospyrobezoar, are better off avoiding persimmons, especially those that haven't lost all signs of astringency.

Storage

Various Asian persimmon varieties can store for up to 5 months, but if you wish to store them long term, they should be harvested quite early.  The optimal color for storage can vary between varieties (or even location and season), but it appears that once they are no longer green, they are ready for harvest.  Some varieties are mature enough to ripen off the tree while they are still entirely green, but harvesting them at this stage, or fairly close to it, may prove to be unwise.  Harvesting too early may cause them to become sensitive to chilling injury below the temperature of 41F/5C.^[10][25] When storing persimmons, another thing to consider is that they are very sensitive to ethylene gas and are best stored without the presence of other climateric fruit.  They tend to produce a much greater amount of ethylene than persimmons themselves.^[26]

The relative humidity of the storage unit should be between 85-95%.^[10][27] 32F/0C is generally recommended, but some varieties, such as Fuyu, may receive chilling injury at this temperature, regardless of the stage they were harvested.  This is, however, not consistent.  Studies from multiple regions have had success with the long term storage of Fuyu (some of which were harvested while they were orange) at the temperature of 32F/0C, while others saw failure in less than a month or two.^[27] Furthermore, Asian persimmons, whether they are chill sensitive or not, may have a higher chance of being injured when the storage temperature is set closer to ~41F/~5C.^[28][29][30]

Chilling injury can cause Asian persimmons to develop a brown discoloration, a metallic or chlorine-like odor, a mealy or gel-like texture, and a loss of flavor, sweetness, or juiciness.^[30] It may also accelerate the loss of firmness or cause the persimmon to dramatically reduce its firmness within a few days after being removed from cold storage.^[29]

Overall, there is a lot of variation in the recommended method of storing Asian persimmons based on the various studies that have been released.  They can, however, be used to guide us toward the most appropriate method for the varieties we grow in our particular region.

While it may not be a practical solution for the average home-grower, commercial growers are capable of avoiding injury to chill sensitive varieties through various methods, such as the use of the ethylene action inhibitor 1-methylcyclopropene (1-MCP)^[29] and adjusting the concentration of one or more elements, primarily oxygen and carbon dioxide, in a modified atmosphere polyethylene bag.^[25][31][32]