Parajubaea is a genus of three species of large, very tropical looking feather palms from the Andes. P. cocoides, the most common species, is from Ecuador, and P. torallyi and P. sunkha are from Bolivia. P. cocoides is known to be hardy to about -2°C/29°F when young, but may recover from temperatures as low as -9°C/16°F at maturity. It is a magnificent palm but generally too tender for our region except in southwest Oregon.
The other species are less well known in cultivation, and have only recently been introduced on a large scale. P. torallyi grows at elevations as high as 11,700' and has two forms: var. torallyi and var. microcarpa. Of these, var. torallyi is generally considered to be superior, being larger and more vigorous with many fronds in the crown. Var. microcarpa is also fantastic, though and still very much worth having. Seedlings of this species have proven hardy down to at least -6°C/21°F, and, being that much superior to P. cocoides, it is likely that P. torallyi may grow in some milder areas west of the Cascades. P. sunkha is a smaller palm found at lower elevations and might be expected to have similar in hardiness to P. torallyi var. microcarpa, or perhaps a little less.
Parajubaea seeds take a very long time to sprout, and germinate erratically over a period of 6 months to 12 years. The seeds are very large (epecially those of P. torallyi var. torallyi, which have three distinct ridges) and the relation to coconut palms is very much evident. They do not really need a lot of heat to germinate, but benefit from some fluctuation between day and night temperatures: a range of 10-25°C/50-77°F might be ideal. Some say the seed should only be buried about halfway. They make a large, deep taproot and should be placed in deep pots. They grow moderately quickly when young, and when the mature leaves start forming growth really speeds up. The best approach to growing this palm outdoors might be to plant it at a relatively small size so that it can get established, and be prepared to protect it from cold until it has a substantial amount of trunk, which is not that long of a wait. Parajubaea should always be planted in full sun. It does not need hot conditions to grow well and might do at least as well on the foggy coast as inland.
So, I would rank Parajubaea
hardiness as follows:
P. torallyi var. torallyi: the hardiest, its limit not known
P. torallyi var. microcarpa: might be just about as hardy
P. sunkha: not really known
P. cocoides: expect heavy damage to mature plants below -4°C/25°F
This order is not really certain, but would seem to make sense.