Some Drosera species have relatively
large hard seeds that are difficult to germinate. The
species I have had the most difficulty germinating are Drosera
D. stolonifera ssp. stolonifera, and D. glanduligera.
The Seed Bank was sending out these seeds to dozens of members
and I couldn't get them to germinate reliably myself. The
had was leaving the D. stolonifera ssp. stolonifera seed pots in my
Sarracenia trays for 18 months. And even that was more
miss than hit. Drosera gigantea? Once. D.
Why would plants produce seeds that are very hard on the
outside and tend not to want to germinate? That is
a characteristic of many plants in Western Australia and
other desert and semi-desert locations. The seeds can
sit in the soil for many years without germinating—sort
of a natural
waiting for the right time. The right time or some event
happens and we get germination. It could be
a bush fire. It could be an exceptionally wet year.
be the seeds have been there long enough and enough of the
seed coat has worn off that it is now or never. For whatever
reason, we have to duplicate what the seeds expect in their
native location in order to get them to germinate.
Getting difficult seeds to germinate is not just a problem
for growers of tuberous Drosera. Many species of significant
commercial value also have hard seeds and ways have been
worked out to get them to germinate. Professor Ellen Sutter
of the Pomology Department at UC Davis
the Drosera seed
planting them. There are many techniques for scarifying
seed from soaking in sulfuric acid or boiling water to nicking
individual seeds with knives, files, or sand paper to rolling
with sand in a rock polisher. Ellen felt that using sand
paper on a sanding block over bond paper would be the easiest
to use and as effective as any other treatment.
Before you decide to scarify your seed, look at them closely
with a hand lens. They should be and look hard. Not all tuberous
Drosera species have hard seeds. Drosera stolonifera ssp. stolonifera seeds
are hard and look similar to the D. gigantea seeds,
only rounder. D.
stolonifera ssp. rupicola seeds look
like they have been popped and have a soft seed coat. There
is no need to to scarify D. stolonifera ssp. rupicola seeds.
Attempting to scarify D. auriculata, D. macrantha, and others
will destroy the seeds.
You can see the tools with before and after pictures to
the right. The sanding block is a hard rubber block
commonly found in hardware and lumber stores. It probably
isn't necessary but makes the job easier. The sand paper
is 100 grit. An engineer could probably calculate the optimal
sand paper grit size to seed size. I'm no engineer but 100
grit seems about right to me. If there is a different grading
bond paper or any other soft, non-coated
paper. Look at the seeds with a magnifying glass or hand
lens to see what they look like before scarification. Then
lightly roll the sand paper over the seeds. The soft paper
will help hold the seeds and the sand paper grit will nick
or otherwise remove some of the seed coat. I don't press
just use the weight of sanding block. After
seconds, look at the seeds and the paper. You don't
want to end up with D. gigantea flour! Look to see
if the seeds are losing their shine and if the paper is starting
to look a little dirty. Do it some more if necessary.
The Seed Bank seeds are NOT scarified before you get them.
That is because scarified seeds should be planted immediately.
You may not get the seeds at the right time of year for planting.
Save them until the right time to plant them, scarify them,
then plant them.
Scarification isn't the whole story for these species. In
the carnivorous plant literature and folklore, it has been
tuberous Drosera species
require a period of warm stratification before the seeds
will germinate. I
have confirmed that seeds of "easy" species such
auriculata and D. peltata won't
germinate if planted in the fall. They need to be planted
in the middle of summer for best germination in the fall.
And it isn't good enough to put them in a greenhouse. Seeds
planted under greenhouse conditions in the summer do not
germinate readily while seeds exposed to higher and lower
out doors can produce a carpet of seedlings when the season
turns to fall. I am being somewhat vague here because I don't
know exactly what is required. In my experience, it
seems the seeds require a month of daily temperatures above
(85°F), possibly a number of days above 35°C (95°F)
is required. The seeds then germinate when they
as a week
(65°F). Some species such as D. glanduligera may
cue in on night temperatures on the order of 7°C (45°F).
Other species may want temperatures around freezing.
Getting seeds of these species to germinate is the first
battle in growing them successfully. Stay tuned to this page
for updates on experiments in progress...
Another D. gigantea seedling in
December after the pots were moved into a sunny location
without the covers.
Drosera gigantea seeds ready to be scarified with
100 grit sand paper and sanding block. Don't press
or you'll get flour.
Drosera gigantea seeds
on bond paper before scarification.
Drosera gigantea seeds
on bond paper after scarification. Note the seeds are dull
and the paper is looking dirty.
D. gigantea and other tuberous Drosera seeds
planted outside the last week of July. The
large pots are sitting in 1 cm of water in a mostly shady
small pots in zip lock bags have seeds of Drosera glanduligera.
Note that you should not use the covers or bags if the pots
will get more than a tiny amount of direct sunlight—you will
end up with roasted seedlings. The trays
are almost completely shaded by an Apricot tree during our
very hot summer. The picture
was taken in late October as the seeds were germinating
tree was starting to lose its leaves.
(Note months mentioned
correspond to appropriate times for northern hemisphere Mediterranean
climate regions. A greenhouse may be necessary to provide
needed conditions in colder climates. In warmer climate
may need to grow species or selections that are more tropical.)
D. gigantea seedling in October under
shady conditions. This plant germinated during a brief
cold (18°C) spell in August between weeks of temperatures
in the 35°C to 40°C range. Many of the seedling's
brethren didn't survive the heat.