Drosera species that could be classed as subtropicals
are found in South America, southern Africa, southern and
eastern Asia, and Australia. There are at least a hundred species
of Drosera in these regions. Some such as the tuberous, pygmy, and woolly sundews of Australia and a few Drosera from South Africa are special cases that need
to be considered separately because of their particular requirements. But
most subtropical Drosera are just variations on the same theme. They have been referred
to as DRS's or <expletive> rosetted sundews because they
are so hard to tell apart without ripping off leaves and checking
flowers and seeds under a hand lens.
Among Drosera species, the subtropicals usually make the
best terrarium and greenhouse sundews. They generally
do well in a moderate temperature range of 10°C to 35°C
to 95°F) and don't have dormancy or light cue requirements to survive long term. They may need light queues to bloom but you do not grow these Drosera for the flowers. Subtropical Drosera do tend to prefer higher humidity than is typical in houses and want more light than they can get on a window sill. But there are successful growers who keep their plants under artificial lights on shelves away from drafts.
Subtropical Drosera in a terrarium.
Many subtropical Drosera are long lived. You can keep most species indefinitely with repotting every 5 years or so. Even annuals such as Drosera burmannii can
live for years if you remove flower stalks as soon
as they appear and feed them well. If the plants do start to decline, propagating is easy from stem, root, or leaf cuttings. Root and stem cuttings will give you new mature plants relatively quickly. Leaf cuttings are not as quick but faster than seeds.
Most subtropical Drosera are not very picky about
soil. They can grow well in pure Sphagnum moss, live, long fibered
or shredded, as well as the standard peat:sand "CP
mix" which can be anything from 30% to 100% peat. Growing
plants in CP mix with live sphagnum on top is very effective for
the larger or stalk forming species. Things to watch for
are inferior grades of sphagnum and peat and non-silica sand. Read the bags carefully to make sure there is no added fertilizer.
The best Sphagnum is from New Zealand and Chile. For peat
look for Canadian or German Sphagnum peat. The best
sand is uniform size sand-blasting silica sand about 1.2 mm in
diameter (12 to 16 mesh in USA).
Everyone has their favorite seed planting medium. They also have
anecdotes to tell why their way is so wonderful and the way everyone
it is, well, you know. You just have to find what works best
for you given the materials you have available and the conditions
provide. You can try a high proportion of sand, putting sulfur
in the soil, using sterilized material, waving a magic wand. They
all work for some people. And then there are pots. Don't get me
started on pots! Some people have obsessions about round vs. square,
tall vs. short, large vs.
small. IT DOESN'T MATTER. Mostly.
One thing there is no argument about is you sow seeds on
the surface of your medium of choice. Don't bury the seeds. For any
seeds but bog plant seeds, you don't top water a seedling pot.
With Drosera it is different. The soil surface should be lightly misted after the seeds are placed.
It helps germination and settles the seed around large sand particles.
Make sure you label the pots and include the date so when it seems
like forever since you planted the seeds you can see it has only
been a few weeks. Some seeds may take a month or more to germinate. Some do require warmer or cooler temperatures so if one location is not working, try a different one.
What you do next depends on what works best for you. Everyone has their
own preferred routine. I put pots with seeds in plastic zip-lock bags
under but not too close to fluorescent lights. You could also use an aquarium in a greenhouse. The purpose of the plastic bag is to maintain very high humidity and to keep out fungus gnats. Fungus gnat larvae will eat the seedlings. A temperature between 20°C
to 25°C (70°F to 80°F) works best for most subtropicals. The seeds should germinate in a few weeks. When the new plants have a few true leaves, you can remove
the pots from the plastic bags and put them in a bright terrarium or greenhouse. Or just leave them in the bags for up to a year. Please see Sowing Seeds Step-by-Step for more details on starting seeds.
Most Drosera seeds are small and result in tiny, slow growing
seedlings. It takes patience to grow carnivores from seed. The
biggest problem in starting seeds is usually dealing with the moss,
naturally in the Sphagnum and peat. It is not uncommon to
transplant seedlings into new media a few times as the seedlings
get overwhelmed with guk. Use a fine forceps, bright light,
and magnifying glass. Be careful not to damage the roots.
Once the plants are large enough you can try feeding them small
insects or get some dried blood worms at a pet shop. The dried
worms can be dipped in water and placed on the dewy leaves—only feed a plant that is dewy and only with live or wet food. If the food gets moldy, use less
time. A dab of 70% isopropanol (rubbing alcohol) from a small
paint brush will help control the fungus.
Do not put fertilizer of any kind in the soil. If it it does not directly kill the plants, it will change the soil chemistry which may make the plants rather unhappy. Once the plants are more than a cm wide they do respond to light misting with dilute, high nitrogen fertilizer. It is best to use hydrated dried blood worms on the leaves instead of spraying with fertilizer, but if you feel you must use fertilizer, use foliar fertilizer with care.
It can easily take two years to get mature plants. The hardest part is getting the seedlings to a size you can feed them with hydrated dried blood worms. Once you can do that the plants should grow quite quickly.
-- John Brittnacher
For more information please see:
About Carnivorous Plants: Evolution -- the Caryophyllales Carnivores
Christophe, Alain (1981) A South African Insectivorous Plant Trip. Carniv. Pl. Newslett. 10(4):96-101 (
Chandler, Graeme (1978) The Uptake of Digestion Products by Drosera. Carniv. Pl. Newslett. 7(1):11-13 ( Part 1
Chandler, Graeme (1978) The Uptake of Digestion Products by Drosera. Carniv. Pl. Newslett. 7(2):51-54 ( Part 2
Nolan, Garry (1978) On the Foraging Strategies of Carnivorous Plants: II. Biological Stimulus versus Mechanical Stimulus in the Fast-Moving Periphery Tentacles of the Species Drosera burmanni. Carniv. Pl. Newslett. 7(3):79-81 (
Haberlandt, Gottlieb (from Sinnesorgane Im Pflanzenreich, Trans. By Carla R. Powell) (1982) Insectivores: Drosera and Drosophyllum. Carniv. Pl. Newslett. 11(3):66-73 (
Degreef, John D. (1989) Early history Drosera and Drosophyllum. Carniv. Pl. Newslett. 18(3):86-89 (
Degreef, John D. (1989) The Droseraceae during the glaciations. Carniv. Pl. Newslett. 18(2):45-46, 52-54 (
Drosera aliciae. These plants are 5 cm across.
Seedlings with one true leaf.