germination of this genus is quite tricky and all who have tried would agree
with this. Several ways have been tried, sometimes very different and based on
different ideas and speculation on the requirements of these 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.
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 refridgerator
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 & Pediocactus in Cactaceae;
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, I cannot express an opinion on its efficacy.
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 frequent checking of the bags necessary and,
as well as being quite frustrating for the impatient, it’s 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 radicle.
a first attempt in Spring 1999 on a batch of 20 P.
cocoides, I sowed the seeds directly into pots but even this
didn’t 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 moldy. Not knowing at which stage each seed was at, the soil 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.
would never consider cracking the shell to sow naked endosperms, as someone
suggested with Jubaea or Butia yatay—firstly because it’s
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 doesn’t imply that it is waterproof, and actually
the pore from where the radicle will push is almost as thin as paper.
1. A box with germinating
(Click on photos to enlarge.)
I decided to try something different. Perhaps inspired from the seeds size, I
sowed new batches of 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, because
this covering doesn’t store much heat at night, so night indoor temperatures
are barely few degrees above outdoor ones. Conversely, daytime maximum
temperatures can be significantly higher than outside the greenhouse.
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, despite most
current advice and considering 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 v. torallyi, 6/80
(8%) of P.
microcarpa,1/30 (3%) of P.
and 6/10 (60%) of P.
2. Family group, showing
3. Parajubaea torallyi
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 temperature at night has been 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.
and nine more a week later;
torallyi v. torallyi and
sunkha, 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 (Fig. 1). In August 2002, the
result has been 69 of P. torallyi
microcarpa, 32 of P. torallyi
torallyi, 25 of P. sunka,
so a rate of over 80%. Not bad indeed!
process seems to imitate habitat conditions rather well—a dry, cool winter and
a moist, hot summer—which 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 germination.
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 over-watering 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, it’s 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 waterings, as they are sensitive to rot. The first
leaf will appear some weeks later (Fig. 2).
not uncommon to find seeds with two embryos, especially with the variety torallyi, and this feature has been observed many times in related genera
Attalea). Leaving them to grow together could give an unusual effect in
years to come (Fig. 3), 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.
Voilà! (See Fig. 4.)
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 (Fig. 5).
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 aren’t old specimens in cultivation outside
habitat—Parajubaea are surely some of the most promising new palms for
Figure 4. Step-by-step procedure for separating twin seedlings.
|Figure 5. Seedlings suffering greenhouse cultivation.|
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