Savage Garden: Slack-Potting the Dewy Pine
CPN 29(4): 101-102
California Carnivores 7020 Trenton-Healdsburg Road Forestville,
CA 95436 USA
Keywords: cultivation: Drosophyllum lusitanicum.
Over twenty years ago, British nurseryman Adrian Slack
originated a rather clever way to successfully grow the often temperamental
dewy pine (Drosophyllum lusitanicum). Glaringly omitted from my
own book, The Savage Garden, I wish to correct that oversight here, for
this method, called "Slack-potting"--a term coined by Barry
Rice--is an ingenious method of cultivating Drosophyllum
with long-term ease.
We must remember that dewy pines are not wetland plants
like most other carnivores. Instead, they are typically found on sandy,
gravel slopes that are dry most of the year, and usually alkaline in pH.
The plant is found in widely scattered sites in Portugal, Spain, and Morocco.
The climate is warm-temperate and Mediterranean, which means that most
of the rainfall occurs in the cool winter months, with very rare frosts.
Summers are warm and dry, but plants near the coast can experience early
morning fog drip, which may be absorbed by their leaves.
Seed is usually the only way to propagate Drosophyllum
(but see CPN 17:4 p106--ed.), and since plants despise root and stem disturbance
they are never sold through the mails. Seed is usually produced in late
spring or early summer and can germinate readily if very fresh. Older
seed benefits from several methods of pretreatment. You can scarify the
hard seed coating by rubbing the black, egg-shaped seeds with sandpaper
until the whitish interior becomes slightly visible. You can also soak
the seed for a day or two in a cup of water in which you have added a
tiny bit of powdered gibberellic acid--about 0.5 cm (1/8 inch) collected
on the tip of a toothpick works well. I have also scarified the seed and
then soaked them in a solution of one-drop Superthrive™ per cup
Slack warns against moving freshly germinated seedlings
about, and prefers to sow a few seed directly in their permanent pots,
allowing only one plant to grow by removing any others that germinate.
This can be a hassle and waste of seed if you have more than just a few
to sow, but Slacks warning is legitimate since the first tiny root
to appear from a seed will rapidly plunge into the soil medium and can
be killed if disturbed. I prefer to sow numerous seed on damp vermiculite
(they will germinate on any damp substance, even a sponge) and I check
them daily after a week or two. When I see the first white root appear
on a seed, I immediately and gently remove it via forceps and set it upon
the surface of its permanent pot.
Now this is where the Slack-potting begins. Take a 10-15
cm (4-6 inch) pot made of unglazed terra-cotta clay. Place a wad of damp,
long-fibered sphagnum moss through its drainage hole, totally blocking
it. As a soil medium, I use one part each perlite, vermiculite, and horticultural
sand to be excellent. Slack includes a portion of John Innes Compost #2
(a humus-based house plant soil), but I find this component to be unnecessary.
(It is only available in Britain.) Dampen the mix with purified water
and fill the clay pot firmly with it to the brim. Gently place your germinated
seed on the center surface of this, one seedling per pot. Place the pot
in a shallow water tray in a sunny place with good air circulation, keeping
the soil damp to wet for several weeks as the plant establishes itself.
Let the baby plant grow for several weeks, as Slack recommends,
before proceeding with phase two. The plant will grow rapidly and when
it has several leaves you are ready to Slack-pot it.
You will need another pot with drainage holes at least
two inches larger than the pot containing the plant. Slack recommends
another clay pot, but in hotter, drier climates like California, I use
plastic. Block the drainage holes with long-fibered sphagnum. Fill the
pot with the perlite-vermiculite-sand medium only as deep as to allow
the smaller potted plant to sit comfortably on the medium and have its
rim at the same level (or just slightly above) as the larger pot. In the
gap between the two pots, tightly pack long-fibered sphagnum.
The whole reason for this elaborate double-potting is
to keep the soil around the stem and upper roots on the dry side, or just
barely damp, since the prostrate stems tend to rot if left on permanently
wet soils. Initially you can keep the whole double pot in a shallow tray
of water as well as gently watering the plant itself, keeping the soil
damp. But in a very few months the roots of your dewy pine will enter
the soil of the larger pot through the sphagnum-crocked hole of the smaller.
You can then water the plant via the sphagnum-moat that separates the
two pots. Alternatively, you can set the Slack-potted plant in a shallow
water tray, and water by the tray system only enough to keep the sphagnum-moat
damp. Just enough moisture will permeate the inner clay pot to keep your
dewy pine happy, and the deepest roots will find plenty of moisture in
the medium of the larger container. This probably recreates the natural
situation well, for in the wild dewy pines have roots that are extensive,
obtaining moisture from deep underground. Some also believe the plants
absorb moisture in summer from condensing early morning fog, but misting
the plant is not required.
Slack-potting a dewy pine works best for greenhouse cultivation,
particularly in humid climates with long, cool winters, such as Slacks
own England. It is not quite as necessary if you live in a Mediterranean
climate similar to the dewy pines. I have seen photographs of huge
Drosophyllum plants grown in giant clay pots outdoors in Australia.
Geoff Wongs prize winning plant photographed in The Savage Garden
was a judiciously watered specimen grown in a plastic pot of primarily
perlite and a tiny bit of peat, then placed in that lovely glazed ceramic
ornamental. I myself grew one outdoors on my deck in northern California,
using a plain clay pot. The plant survived months of winter rain, a hard
freeze, and baking summer heat (see my 1995 column, "How to Torture
a Carnivorous Plant", CPN 24:4, p99.). So while not for everyone,
for many growers Slack-potting is ideal. At my nursery just this past
week we Slack-potted several dewy pines. In my imagination, I visualized
Adrian visiting us in his white suit and Panama hat, nodding his approval
as we shared a glass of wine.