Early Conclusions on Germinating Parajubaea
Angelo Porcelli, Bisceglie (BA), Italy
Chamaerops No.48 - published online 24-05-2004
Parajubaea cocoides enjoying the sunshine in Quito, Ecuador.
Photo: Tobias W. Spanner
The germination of this genus is quite tricky and all who have tried would agree with this.
Several ways have been tried, and sometimes very different as they are based on different ideas and speculation
on the requirements of this species. Failure has been common. But the method I have been using (after more than
one year of trials and observations, reading about habitat conditions, message board interactions, e-mails with
many other palm folk sharing opinions and partial results) has given me, at last, a fairly good result.
The first consideration is pretreating the seeds before sowing. It has been confirmed by many that letting the
seeds dry for some weeks improves germination significantly. On this I have added cold storage for 4 weeks in
a refrigerator at 4°C. This has given me excellent results with palms from temperate climates (Brahea, Butia),
which I have sown by the thousands, and recently with a large batch of Trithrinax campestris. The cold storage
of seeds is a common technique used by growers of other plant families and, indeed, it is needed for some plants
from peculiar habitats (i.e. Sclerocactus and Pediocactus in Cactaceae; many Mesembryanthemaceae-Aizoaceae;
After this, the usual soaking in clean water for several days has been followed. I have also added a germination
stimulator based on NAA, but, not having a control batch to compare it to, I cannot express an opinion on its
At this point, opinion divides. Some growers have used the well-known bag method, which does work well for many
species, especially the small-seeded and tropical ones. But with Parajubaea, it has some drawbacks. Firstly,
as it is difficult to know when the radicle will appear, it may grow several centimeters in the bag and become
difficult to pot up due to its odd shape. This makes it necessary to check the bags frequently, which is not
only quite frustrating for the impatient, but also a bit dangerous, as the eventual shoots can be damaged by
exploring fingers. But the real problem is that the medium used (peat) allows fungi to grow on fruit that remains
trapped in the grooved surfaces of the seeds and this can have devastating results on the seed and emerging
In the spring of 1999, on a first attempt with a batch of 20 P. cocoides, I sowed the seeds directly into pots,
but even this didnt give me good results. On this batch, I tried to scarify the seeds with physical and
chemical methods (filing the shells of 10 and soaking the others in sulfuric acid) but this was a bad idea because,
in the end, the other unsprouted seeds became mouldy. Not knowing at which stage each seed was, the watering
schedule could not be optimized for both germinated and ungerminated seeds. I ended up with only four plants
from this batch and was not satisfied.
I would never consider cracking the shell to sow naked endosperms, as someone suggested with Jubaea or Butia
yatay, firstly because its almost impossible to crack a P. torallyi shell without damaging the seed, and
secondly, the naked endosperms are easily attacked by fungi. This method could only be used in laboratory conditions.
On the other hand, Nature has designed the seeds so that they will be spread on the bare ground without killing
them and if these seeds have such a hard shell there must be a valid reason. Also, a thick shell doesnt
imply that it is waterproof, and actually the pore from where the radicle will push is almost as thin as paper.
So, I decided to try something different. Perhaps inspired from the seed size, I sowed new batches of P. torallyi
v. torallyi, P. torallyi var. microcarpa, P. sunkha and P. cocoides again, using the highly successful method
I use with cycad seeds. This consists of using polystyrene boxes with lids and that are 20 cm deep (the kind
used to pack cheese, fish etc.), filled with pure perlite to a depth of 10 cm. The seeds are laid on the surface
sideways with the point down, buried a third of the way. Then the perlite is gently watered with a fine hose,
the lid is put on, and the boxes are put on a shelf 1.90 m above ground in a cold greenhouse covered with clear
plastic and 90% shade cloth. This means that temperatures follow the day-night range, with very little difference.
The covering doesnt store much heat at night, so night indoor temperatures are barely a few degrees above
outdoor ones. Conversely, daytime maximum temperatures can be significantly higher than outside the greenhouse.
Here, I put a min/max digital thermometer with two sensors, and I have recorded the temperature data inside
and outside the boxes. From these data, one thing has become evident. These species like high temperatures to
germinate, contrary to the most current advice and despite the montane habitat of the genus, which would suggest
lower temperatures. This could also be the case for other genera (e.g., Trachycarpus and perhaps Ceroxylon).
I have never recorded any sign of activity when the maximum temperature was under 26°C, and the peak of
germination has been in the range 14°C-35°C. This is easily obtained from late spring to early autumn.
In the first trial last year, I achieved the following success rates: 11/40 (28%) of P. torallyi var. torallyi,
6/80 (8%) of P. torallyi var. microcarpa,1/30 (3%) of P. sunkha, and 6/10 (60%) of P. cocoides.
When I found no new germination after three weeks, around late October 2001, I stopped misting the seeds. The
lids were removed, allowing the perlite and seeds to dry out totally. The boxes were left to over-winter. For
a period of over one month, in January 2002, the minimum nighttime temperature was constantly in the range of
1°C 4°C. In early March, the temperatures rose, fitting into the optimal range. So, the perlite
was watered again and the lids put back on the boxes. At the first check, after a week, most of the remaining
seeds were germinating: 39/74 of P. torallyi v. microcarpa, and nine more a week later, four P. torallyi v.
torallyi and two P. sunkha, and then a wave of 11 P. sunkha at a later check and still continuing. I also found
four seeds rotten, easily recognized by the white mould growing on the tip, smelling of rotting coconut. In
August 2002, the result was 69 of P. torallyi v. microcarpa, 32 of P. torallyi v. torallyi, and 25 of P. sunka,
which means a rate of over 80%. Not bad indeed!
This process seems to imitate habitat conditions rather wella dry, cool winter and a moist, hot summerwhich
suits the seeds. Another consideration is that, in the northern hemisphere, we usually get fresh seeds around
late winter, while in habitat it is the opposite season. I believe that the poor results I got initially resulted
because the seeds should have quite a long period of rest, helpful to induce/remove some chemicals to trigger
The box technique means not having to bother watering the seeds. I just mist them with a hand sprayer when they
are dry (the shells turn from dark to light brown). There is no risk of under- or overwatering because, with
the lid on, the evaporation is minimal and moisture is held constant. Also, no problem occurs if one overlooks
weekly checking for sprouts, as I often do. The radicle grows straight down in the moist yet porous perlite,
and no harm will be done pulling up the germinated seed. When the radicle is 4-5 cm long, its time to
pot it up. I use tall, square pots (10x10x20 cm) filled with a mix of peat/sand/perlite in equal parts. A bit
of care is needed for the first watering, as they are sensitive to rot. The first leaf will appear some weeks
Its not uncommon to find seeds with two embryos, especially with the variety torallyi, and this feature
has been observed many times in related genera (Butia, Syagrus, Jubaea, Acrocomia, Attalea). Leaving them to
grow together could give an unusual effect in years to come, but any attempt to divide them after the germination
stage would be fatal for the palm! An easy trick can be used to get two independent plants. Once the radicles
are of the right length, I put the seed on the edge of two pots, joined side by side with heavy tape, allowing
each root to go in its own pot. A small square pot of 7cm, with the bottom cut off, is placed over the two pots
and is inserted with the help of two notches. The remaining space is filled with the mix. This is to prevent
the hypocotyls from drying out or being damaged accidentally. After about a year the seed will be spent and
the two pots can be separated. And then & two plants for the price of one. Voilá!
All Parajubaea species need to be grown in full sun outdoors from the first leaf stage, at least during the
warmest months, as they resent greenhouse conditions (lack of air movement and high level of humidity). Otherwise,
they develop weak leaves with yellow stripes, which bend and die slowly. This also indicates the adaptability
of this genus to subtropical areas with moist summers. While the ultimate cold hardiness of the several species
is still to be well tested, as there arent old specimens in cultivation outside habitat, Parajubaea are
surely some of the most promising new palms for temperate climates.
Reproduced with permission by the author from the Palm
& Cycad Societies of Florida, Inc. Have a look at their award-winning Virtual Palm Encyclopedia
for a wealth of information on palms and cycads.
25-04-15 - 15:57GMT
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