Native Range and Climate

Pomegranates are native to Iran and the drier half of south Asia, but they have been extensively cultivated in Caucasia, other parts of the Middle East, and the Mediterranean basin.  Rainfall within their native region is near 0" for 4 months in the middle of the grow season and 1" to 1.5" per month during the rest of the year.  While established plants can tolerate severe drought and extreme heat, irrigation is necessary if you wish to get a good crop, but heavy irrigation during bloom may encourage the flowers to drop.  It will also encourage mature fruit to split if done after a dry spell.

Pomegranate varieties are often hardy down to 12F (-11.1C), but the most cold hardy can survive temperatures down to 7F (-13.9C), possibly lower.  Young trees may be more sensitive to winter cold, and temperatures around 28F (-2.2C) will often kill pomegranate trees above ground if they are awake from dormancy.  Since they are propagated through rooted cuttings rather than grafting, you'll retain the same variety, but they may not fruit again for a few years.  Bud break seems to happen quite early, but I currently don't know what to compare it to.  The fruit of those that do manage to survive in the east often suffer from fungal problems due to the wet climate, but some of them manage to be spared.

Disease

Heart rot, predominantly caused by the fungus Alternaria alternata, is the most serious pomegranate disease.  Spores infect the pistils of open flowers and grow down the tunnel to reach the inside of the fruit.  From there, they remain latent until later in the ripening process, when the fungus begins to rot the arils.^[1] From the outside, the fruit looks healthy, but infected fruit are lighter in weight and emit a hollow sound when knocked (rather than the dull sound of healthy fruit).  It may also cause a slight discoloration of the skin.^[1][2]

Colonization of A. alternata in the pistils of asymptomatic pomegranates can be significant, with some found in the tunnels as well.^[1] The reason why the arils are spared from infection is not entirely known, but it's possible that the situation is similar to core rot in Red Delicious apples.  Apple core rot is also caused by A. alternata and was noticeably worse in light yielding trees.  Those that produce a lighter crop have heavier shoot growth, larger fruit, and, as a result, a lower calcium concentration in the fruit.^[3] Calcium is believed to inhibit an enzyme produced by A. alternata needed for the fungus to grow.^[1]

Heart rot in relatively dry climates seems to infect roughly 10-20% of the fruit on untreated trees in well established orchards,^[1][2][4] but an incidence of up to 50% has been reported.^[5] In wet climates, it's difficult to say, but it appears to be significant.  However, the examples I have heard about come from people who regularly experience dieback, so light cropping might have something to do with it.

Cases of heart rot can be reduced by various fungicidal treatments.  In Cyprus, Wonderful pomegranates from control trees in two different orchards had an average heart rot infection rate of 8.8%.^[6] Trees sprayed twice with copper oxide, 7 weeks apart, before bloom had an infection rate of 4.2%, and trees sprayed twice during bloom with a Propiconazole + Difenoconazol mix, 2 weeks apart, had the lowest infection rate of 2.4%.  Copper oxide is used before bloom since it is known to cause negative effects on the flowers and fruit set.^[6]

Pilidiella granati, also known as Coniella granati, has recently become a fungus of high concern in various parts of the world.  It can infect the fruit, leaves, twigs, stems, and the crown of the bush.  Mycelial growth is most significant between the temperatures of 77F/25C and 86F/30C, causing infection to become apparent when the fruit is at least half-grown.^[7] They will develop dry, dark brown lesions that expand quickly, which ultimately leads to the mummification of the fruit.  Heavy losses can be attained before harvest and in storage,^[7][8][9] since the disease can be spread to undamaged pomegranates if they are in contact with infected fruit.^[10] The disease, however, spreads slowly when stored at the temperature of 41F/5C, and in one study, inoculated fruit showed no signs of infection during the entire 42 day duration observed.^[11]

Orchards with good sanitation practices may have a considerably lower incidence of disease.  In the Solan district of India, where mummified fruit were often seen on the orchard floor, the percentage of diseased fruit was roughly double of the other two districts observed (~20% vs ~10%).^[9] However, the weather may have played a role on both years studied.^[9] Further evaluations have indicated that overwintering pycnidia (asexual fruiting bodies) were found at a higher rate on mummified fruit than on blighted shoots and trees with symptoms of crown rot (77%, 25%, 19%, respectively),^[7] implying that mummified fruit are the greatest source of infection.

Anthracnose, caused by the fungus Colletotrichum spp, is another serious pomegranate disease that may attack the fruit, leaves, shoots, or twigs, to varying degrees, depending on the species complex.  It is fairly common for dark lesions to begin at the calyx of immature fruit, and as the season progresses, sunken spots will form throughout, provided the conditions are right.  The disease thrives in humid climates and is most active between the temperatures of 68F/20C to 86F/30C.^[12]

In a three year survey in the southeast (US), anthracnose was the pathogen identified to have the greatest impact on yield loss, destroying as much as 90% of the crop, if left unmanaged.  Colletotrichum related anthracnose is also known to infect the fruit and leaves of many other species, some of which have been verified to cross infect one another.^[12]

Pests

The leaffooted bug appears to be the most significant pomegranate pest, primarily because they create entry points for pathogens when they feed.  The adults look fairly similar to stink bugs, but they are more elongated and are roughly an inch in length.  They are strong flyers, long-lived, and produce bright orange-red nymphs that look quite similar to those of the beneficial assassin bug.  Feeding may cause pomegranate arils to wither, and in some regions or years with warm winters, high population numbers can overwhelm the fruit.  Temperatures around 21F/-6C will begin to kill some of the more exposed bugs.^[13]

The omnivorous leafroller may occasionally be a significant pest, especially if grapevines or other more desirable hosts (including various weeds) are nearby.  They, too, are largely a concern for creating an entry point for pathogens.

Seed Firmness

"Hard seeds" may not be edible, but "medium hard seeds" should be (assuming the label is accurate).  Sometimes soft and hard seeds are the only two labels used.  Medium soft to medium hard seeds are often placed in the hard seed label, so this creates some confusion.

Storage

Pomegranates can be stored for roughly 2 to 3 months if the temperature is around 45F (7.2C) and the relative humidity between 85-95%.  Temperatures below 41F (5C) will eventually cause chilling injury to the fruit.  Regardless, people still freeze the arils, so injury is likely insignificant outside of decreasing its ability to sell.

Pomegranates do not ripen off the tree.