How to Grow Tuberous Drosera
Tuberous drosera are fascinating plants, which are arguably the most diverse subgenus of Drosera named Ergaleium. For example, some tuberous sundews are very tiny (as small as some pygmy Drosera), while other species can reach over 1,5 m (4 feet) tall! Also, there are flat rosetted species that grow to 8 cm (3 inches) in diameter, in contrast to some species that develop thin, tall stems and look like a shrub!
Although the cultivation of tuberous drosera is a bit more difficult than the notably easier subtropical species, it is definitely worth the extra effort! If you are a sundew enthusiast and have gained experience cultivating the easier-growing species, then tuberous drosera should be your next frontier!
All the herein mentioned periods, in which should be sowed, potted, repotted and harvested are related to the northern hemisphere (see also: How to adapt tubers from the Southern to the Northern Hemisphere).
One of the extraordinary properties of the tuberous sundews is their ability to build tubers, which offers a very unique means the plants build subterraneous tubers, where they store energy and nutrients for the next growing season.
Tubers of Drosera modesta Manjimup
Coming out of Dormancy
At the beginning of the wet, mild winter in south- western Australia, the plants begin to bud from the tubers and emerge above ground. This process can occur quite rapidly, as demonstrated by the pictures below:
Drosera erythrorhiza (above left) is very small (see the single grain of sand by comparsion) but quickly grew much larger in only 14 days!
The flowers of the tuberous drosera are quite large for the size of the plant and are extraordinarily beautiful. Especially many white flowers have very pleasant-smelling honey like aromas!
When the summer starts again, tuberous drosera begin to develop their tubers and their aboveground parts begin to dry out, as demonstrated in the pictures below:
Drosera macrophylla at the end of the growing season and about one month later.
Apart from brown, dry tuberous Drosera can be more or less colorful or black, too.
Dried out Drosera colina and Drosera prostratoscaposa
Climate and Habitat Information
Nearly all the tuberous Drosera originate from semi-arid regions in the south-west of Western Australia
. These areas become hot and dry in the summer months, but are wet with moderate temperatures in the winter. The plants adapt to this extreme variation of conditions by growing during the winter and than developing subterraneous tubers before the hot and dry summer in order to survive the dry period.
As summertime begins, temperatures begin to rise above 20 °C (70 °F) and the photoperiod reaches approximately 10 hours a day. At this time, all the parts of the plant above the ground begin dying and the subterraneous tubers are formed. Some species like Drosera gigantea form tubers up to 1,5 m (1,5 feet) deep in ground. At this depth, the temperatures are lower than on the surface and there is also residual moisture stored here, even though the surface is extremely dry, like a desert. When the winter time begins, bringing lower temperatures and substantial rainfalls, the tubers start to sprout again. At this time, the photoperiod is between 8 to 6 hours. The areas in which tuberous Drosera grow are usually very sandy.
Average Rainfall [mm]
Click onto the images to get a bigger image.
Average Hours of Sunlight (Photoperiod) [h]
Average Number of Cloudy Days
These charts show the summary statistics for Perth, Australia. The original data are from the Australian Government, Bureau of Meteorology
The Key to Cultivating Tuberous Drosera
The key for a successful cultivation of tuberous Drosera is to closely mimic the conditions tuberous Drosera are subjected to in nature.
Tuberous Drosera are picky about the temperatures. If temperatures drop below 0°C(32°F) and the pot is freezing the plant will die and you can only hope that a few roots survive to build a new plant and that this plant becomes strong enough to form a tuber, when the growing period is over. If the temperature is only for some hours under 0°C (32°F) and not totally frozen even if the dew is freezing there is a chance that the sundew survives.
On the other hand, if tuberous Drosera receive temperatures above 25 °C (75 °F) for one week or longer, the plants will think the dry summer is approaching. In response, they will begin to remove nutrients from the above ground parts of the plant in order to build a subterraneous tuber. At this time, it will appear that the plant is dying.
Therefore the temperatures during the growing season should be between 5 to 20 °C (40 and 70 °F). Mine are kept in the basement of my house at temperatures around 15 to 20 °C (70 °F) at daytime and 10 to 15 °C at nighttime hold winter long and this works well.
In the dormancy season the temperatures should be above 20 °C (70-75°F) but also try avoid temperatures that are too hot. Don’t worry if there are some days with cooler temperatures, but this time shouldn’t be longer than a week or more, otherwise the tubers can start to sprout.
As you can see in the charts above the temperatures in the growing season are less than 75°F at daytime (25°C) with relevant rainfalls and about 8 to 6 hours sunlight. In the dormant season the temperatures are above 75 °F (25°C) with nearly no precipitation.
If you can provide these conditions you will have fun time with your tuberous Drosera :).
In the winter, while the tuberous Drosera are growing, the media remains moist. The easiest way to keep the soil moist is by using the tray method, but make sure that the tubers remain above the water line. Usually this is not a problem since the tubers were planted mostly halfway up pot. But towards the end of the growing season, the secondary tubers develop and in some species (ex. D. gigante, D. rupicola), these tubers are formed deep in the pot. This is yet another reason to give your plants less water when the first signs of dormancy are observed. Usually, if I see that the plant starts to show signs of a beginning dormancy I put these plants in a separate tray, which is left completely dry. In the course of time, the watered tray becomes more and more empty and the dry one is filled up with pots, where the pots are left to dry.
The first time I grew tuberous Drosera, I made the mistake of keeping them in an active growing state for as long as possible. I thought as long as the plants are growing it is better to keep them moist, and I only stopped watering them when they were nearly brown. The result was that many of the tubers rotted. Keep in mind that at the time the first leaves becomes brown, the tubers have already started to form. I know it’s hard to see a healthy plant which seems to die of thirst and not to give it even one drop of water, but they expect and need this.
Than I have read that the pots shouldt be kept totally dry even with no residual humidity. I lost 3 tubers of Drosera zoneria! Some people say that this works well but I wouldt not recommend this. Remember that the plants are building tubers in order to suvive deep in the earth where there is a residual moisture and usually in the middle of the pot automatically a residual moisture will remain.
If the pots in the dry season really seems "too dry" for me than I spray some water onto them, but really very little.
Generally tuberous Drosera are not so picky about the humidity. In the growing season (in habitat) there is between 60 and 80% relative humidity and that’s the range you should try to attain. Humidity can be controlled by a range of options- for example, there is about 100% humidity in a closed glass container and 20-50% in an open glass container in the house (depending on the time of year). While tuberous Drosera can grow in very low humidity, it is not recommended to let them grow open in the house without the tray method because they will produce little to no dew, and won't be able to digest insects/food as easily.
As far as I know there is no tuberous sundew which must be feeded like some other sundews (ex. D. glanduligera) but in my opinion it is better to feed them in order to grow better and stronger.
If you want to feed your sundews it is generally necessary that the leaves are dewy. Do not feed leaves without dew and never use portions for feeding which are bigger than the leave. The small leaves usually have the strong tendency to die after they got too much food. Therefore you have to be very carefull, especially when feeding seedlings or small plants. Rosetted tuberous Drosera usually have only a few large leaves, which are formed at the beginning of the growing season. Some species do not develop any more new leaves, but instead, they only enlarge the initially-formed leaves. Therefore, be very careful to avoid over-feeding the leaves. Large portions of food can cause the leaves to become burnt, sometimes causing enough damage so that the leaf completely dies. Therefore, it’s better to feed them with small portions or with fruit flies. Especially for Drosera with wide and flat leaves, like Drosera erythrorhiza.
I feed all my sundews with fruit flies or with fishfood flakes.
The fruit flies I breed by myself. In webshops for repiles, especially for frogs, you can buy whole sets for breeding fruit flies. It shouldt be wingless or flightless Drosophila flies and they shouldt be as small as possible. Maybe one day I will write an extra page about breeding fruitflies but by then you can find many instructions on pages for reptiles and frogs.
If there are enough flies in the breeding vessel I put the vessel into the refrigerator for about 5 minutes. Because of the temperature the flies become slow and that is very good in order to take them out of the vessel. Otherwise they are very agile and at the end flies are running around at the kitchen table and that couldt give some trouble with other persons in the household what needs to be strictly avoided ;-).
I pour the most of the flies in a well closable container like a plastic cup with a cover and freeze them. If I have enough (about two month of breeding give enough flies for me for the whole year) I stop breeding and if I want to start again I buy some new flies.
To feed the plants I take out some frozen fruit flies and pour them into a cup, put some drops of water onto them and a drop of a fungizide and swill them a little around so that the fungizide and the water is mixed and the flies are covered by the solution. Than I let them stand for a while so that the flies can unfreeze.
With pointy tweezers I take a fruit fly and put it onto a leave. Like this I feed all my sundews which have leaves big enough for fruit flies. Usually I give one or two fruit flies every two weeks onto one plant. It couldt be more but I did not have the time to do so.
I use fishfood which only or mainly consists of animally origin like food for cichlids. I grind it into a fine powder and store it like this. If it should be used I put a small ammount of the fishfood powder into a cup and mix it with some drops of water and a drop of a fungizide. This shouldt result in a pasty mass. With pointed tweezers or another pointed tool like a needle I separte very tiny peaces of this mass and put them onto the leaves. I only use this method for feeding seedlings and plants with very tiny leaves like D. bulbigena.
First of all, the very most fungizides are harmless for carnivorous plants if you use them in the right concentraion. The fungizide is in my opinion very important for feeding the plants. If you do not use it, it is likely that the fruit flies or the pasty mass gets mouldy. As a fungizid I use a solution with Tebuconazole as an active substance. That is an agent for the disease control for roses.
Drosera auriculata and Drosera subhirtella with fly
Drosera magna with fly
Like nearly all Drosera, tuberous Drosera need a lot of light, but they don’t have very high requirements because they are usually growing in the cold season, when the light intensity is low. Plus, as you see on the chart below, the natural photoperiod is between 6 and 8 hours during the period that they are growing.
Growing Tuberous Drosera in a Greenhouse (or using additional lighting)
Therefore, if you grow them in a greenhouse at an appropriate temperature during the winter, you probably do not need any additional light. If the plants don't obtain full coloration under these conditions, this is not necessarily harmful (as long as the plants are still producing dew). If you desire to provide supplemental illumination, it is better to add the additional lighting while the sun is shining rather than extending the photoperiod.
Solely Using Artificial Light
Tuberous Drosera can be grown very well under artificial light, but in this case, the temperature needs to be monitored carefully. Most artificial lights produce heat (most notably T-5 fixtures). This can be a problem, since heat seems to be the most important factor that controls the biological clock of tuberous Drosera. Under artificial lighting, a constant photoperiod of 8 hours in the growing season works well.
In the last years I practiced successfully the following lighting scheme:
Photoperiod [h] under artificial light
Some of the tuberous Drosera do not want to go to sleep! Therefore, apart from the naturally higher temperature in summer and the lack of water, I put the photoperiod for the last ones in June to 11 hours.
If you have the opportunity to put the tuberous Drosera somewhere outside in the garden, on a terrace or anything like that it is recommended to do it. There they can follow the natural rhythm, but you have to take care about the following things:
They should not get too much sun at the beginning. The light intensity of a cloudy summer day is about 20000 lx and more or less the intensity you could and should get under artificial light. At a cloudless summer day in the middle of Europe or the USA you easily get 100000 lx.
Take care of too low temperatures (close to or under the freezing point) or too hot temperatures (75 °F / 25 °C or above) for a couple of days. Take care that the humidity is not changing too fast. If they were in a more or less closed container they are accustomed to a high humidity. Adopt them in about 2 weeks to the humidity outside by keeping them first in a more or less closed container and then open the container day by day a little. Take care, that they are protected against heavy rain. This could be disastrous especially for fine, erect species like D. bicolor, D. zigzagia and so on. I usually let the more picky and rare species and the seedlings under artificial light all the time because I am afraid of loosing them, all the rest of my tuberous Drosera (and pigmy and wintergrowing african Drosera, too) I put to the terrace when the minimal night temperature is not less than 40 °F/5° C.
How to Unpot, Collect and Store Tubers
When and How to Collect Tubers
The important question is when to unpot tubers. The right time is about one or two or three months after all the aboveground parts of the plant became brown and dry. This is usually in May to July. Then the media should be nearly dry. Raise the pot a little to feel the weight. If it is dry it’s much lighter. Turn the pot around so that the media comes out. Carefully tear the media into 2 chunks. Usually you will see the first tubers, because it seems that the media prefers to break at the parts where the big tubers are.
Hunting for Tubers in the Pot
Now a very difficult part starts, the tuber search. You have to crumble all the media and look carefully for small tubers. If you have a species that has dark red tubers, you are lucky. If the tubers are white, the little ones will look just like the sand grains. It is a good idea to orient yourself with the dried parts of the plant and then follow them until you hopefully find a tuber. If you start hunting for tubers too early, the formation of the primary and secondary tubers will not be complete and the roots will still be white and thick. If you disturb the plant in this condition, it’s usually not possible to “re-pot” it. In this case, treat the whole tuber-root like a normal tuber and hope that the tuber-development process will continue. If you don’t break the root in the process, it will usually work out just fine.
Storing the Tubers During the Summer
At this point you have 2 options:
Option 1: Leave the tubers in their pots for the summer
If they should remain in the pot the media may not become totally dry. In nature the tubers are formed deep underground, where there will be residual moisture to keep them alive. So the key is to maintain some residual moisture in the pots- but not too much! This isn't a problem- store the pots somewhere that is protected from sunlight and will not become too hot. A dark place under the shelf in a greenhouse or somewhere in a room is good (or in the garage). During the dormancy period, you should give the tubers daytime temps of at least 75°F (20 °C). If you did not keep them in a place with a high humidity like in a green house it is recommended to give them very small ammount of water, a few drops in a month should be enough. Especially for „young“ tubers in the first dormancy which they are usually formed just below the surface this is recommended.
Option 2: Dig up and collect the tubers for summer storage
If you dug out the tubers, separate them from bigger clumps in order to avoid rotting-- but do not try to separate them forcefully. This can cause damage to the tubers. Some tubers form a papery cover, which are the remains of the former tuber. This is to protect the tuber and should not be removed.
Tubers of Drosera bulbosa aff. El Caballo Blanco form and Drosera intricata
If the papery cover falls apart, then it will usually still be alright.
Some tuberous Drosera build tubers above the ground from the leaves like some clones of Drosera gigantea, which is a normal behavior and some are building tubers on the surface which is probably because the pot is too small.
This is a Drosera rosulata gigant swamp form with a subterran tuber
I usually dig the most of them out which has the following advantages:
If you have the tubers in bags, you have the control to diagnose problems if/when they arise (such as if the tubers start to rot or dry out).
You can be happy about the secondary tubers when they form! That’s always a bit like X-mas :)
Sometimes the secondary tubers are all clumped together. Next time you can plant the tubers at an appropriate distance from each other.
Some tubers were build at the ground of the pot and so they wouldt be under the waterline next season.
Last but not least, tubers make great trading material!
On the other hand, in the nature, nobody digs tubers up (apart from poachers) and they still grow very well. In any case, the disturbing of the tubers is unnatural for them.
Anyway, if your collection of tuberous Drosera becomes huge enough it’s simply a question of time to dig them out or not.
Once you have the tubers, store them according to the following directions:
Storing of Tubers
Keep them in closed containers. Plastic zip bags or small plastic containers work very well. Do not forget to label the bags- or better, put the plant label into the plastic zip bag.
Store them at about 20 to 25 °C (70 to 75 °F).
Put some slightly moist medium into the bag. I usually take some of the media from the ground of the pot, about 5 time the volume of the tubers
Check up on the tubers from time to time (weekly to monthly) in order to see whether they are drying out, rotting or start to sprout.
Only in very rare cases do problems occur. If they are drying out then you can put a well squeezed-out piece of moist spagnum moss into the bag. in order to rehydrate the tuber. I've made this some times and in one case, when I controlled the bag, mould developed and already had overgrown the tuber. In the end, the tuber did not survive. In other cases it works well. So be very careful, and practice makes perfect!
If you will do this than I recommend to sterilize the sphagnum before use, maybe by treating it in the microwave oven. OK, that's not a sterilization, but it surely will reduce the microbiological contamination.
Alternatively, you can re-pot the tuber into nearly dry substrate.
Potting up & Planting Tubers
Pot Height - Use Tall Pots
In the literature, it is commonly mentioned that tuberous Drosera need tall pots. This is very true for adult plants. The height should be at least 4 inches (10 cm). In my experience, this height works very well for almost all tuberous Drosera. It has been reported that if the pot is too short, roots may grow out of the holes in the bottom of the pot. These longer roots usually form tubers, too, so be careful not to break them. However, I've grown tuberous Drosera since 2005 and have never had this occur. For seeds and young tubers, smaller pots will work just as well. I usually sow the seeds in about 2-inch (5 cm) tall square pots and repotting them only if there are too many plants in one pot in 3 or 4 inch (7.5 to 10 cm) tall pots. That works well for many winter growing drosera species as they initially have only short roots and can be placed on fresh substrate easily. Exceptions for this are all Drosera menziesii ssp. and Drosera bicolor. These species produce a long, fine root approximately 1 cm long before showing their first leaves. Still, re-potting these is not a problem if the sowing mix contains lots of sand and just a little peat. At least the top ½ inch (1cm) should not contain too many long fibers which can make repotting a time consuming business. It sounds complicated but it becomes routine in a short time. The tuberous Drosera don’t require wide pots as long as they don’t form large rosettes (such as Drosera erythrorhiza). The 40 tubers in the picture at the top of this page were collected from a single 4-inch-tall (10cm) square pot with a width of 3x3 inches (7x7 cm).
Preparing the Appropriate Soil for Tuberous Drosera
Tuberous Drosera generally require a loose, sandy substrate. I grow nearly all my tuberous Drosera in a mix of one part sieved peat to one or two parts white silica sand (with a grain size of 1 to 5 mm). If you do not want to sieve the peat in order to obtain the finer powder, try to collect some that is not too fibrous. Sometimes the addition of perlite and vermiculite is recommended, but my plants grow well without them. White silica sand (or light colored) is recommended for older plants. When you are looking for small secondary tubers, or tubers of plants which you just raised from seeds, the sand color becomes important. When I first started planting my tuberous Drosera, I used sand that consisted of small green, red, white, beige, brown, black opak and transparent grains. While this coloration is nice for an aquarium, it is a pain if you are looking for small tubers! Even in white sand is very difficult to find white tubers if they have nearly the same size than the sand grains.
Last season I used black colored sand instead of white for the sowing of the tuberous Drosera in order to find the small white tubers better.
This black sand was especially for aquariums and it was written, that it is colorfast and have no influence on the hardness of the water and the pH-value (value for the acidity or basicity of an aqueous solution). The size of the grains was 0.04 to 0.1’’ (1 to 2 mm).
I sowed 10 different species in a mixture of 1:1 peat to sand. Additionally I potted some species of which I had so many tuber that I have to make at least two pots in 1:1 peat to black sand (D. stolinifera, D. rupicola, D. erythrorhiza ssp. collina, D. moorei and more).
Between the pots with white aquarium sand, which I usually use, and the pots with black sand I have not noticed any differences in growth, health of the plants or tuber yield and did not see any deposits.
Of course I can not say if I would get more mini-tubers in the "normal" mixture. However, the yield has been good.
Drosera prostratocaposa in a mixture of peat and black sand
Now to what I wanted, namely to find the white mini tubers better. I must say that I'm highly pleased. Here is an image that everyone who has ever dug tubers, knows or a similar:
That are tubers of Drosera gigantea in the white sand-peat mixture. Because of the colour you can recognize them more or less well.
Drosera gigantea tubers in a mixture of peat and white sand
Here is a picture of tubers of Drosera planchonii tubers which I grow from seeds this season. After three quarters of a year 16 cute, white tiny tubers developed, all about 0.04 to 0.1’’ (1 to 2 mm).
Drosera planchonii tubers in a mixture of peat and black sand
You see that the tubers are clearly visible. Just imagine this tiny tubers in the upper image!
My conclusion: The black, artificially colored sand seems just as good as the white sand. However, it has the disadvantage that it is more expensive than the natural white sand.
The discovery of small tubers, especially the white ones, is much easier than if you used white sand and it is also psychoactive! It has a calming effect, because you no longer have the bad feeling that somewhere in the pile there are still some small tubers which you have forgotten.
Usually on the surface of the substrate sooner or later moss and/or algae will grow. Some people like this and some people not.
When I pot tubers I used for the top 0.4 inch (1 cm) of the media pure white silica sand or more or less white gravel because of the light is better reflected and therefore the roots are kept cooler and algae, moss etc. are discouraged, or will grow more slowly.
Drosera auriculata which is comming out of dormancy and some Drosera zoneria
First the silica sand is purely white and it does look great but later the sand will become more or less brown because of the peat. That is absolutely harmless but it does not look nice. As an alternative you can use crushed lava rock or more coarse gravel, but do not forget to rinse the stones first.
Drosera abberans and Drosera hookeri Lysterfield
Preparing the Soil in Pots
The following is meant for tubers that have already built a stolon and have started to grow. If you want to plant tubers while they're still in dormancy, then use soil that is nearly complete dry and start to water once the first signs of life are seen: First prepare the pot with the media from directly above. The media shouldn’t be sopping wet, but just slightly moist. I usually prepare just enough media for the pots I'm going to use
don’t forget to rinse the media first if using low quality peat). I then press the water out of the media as much as possible and loosen it back up again before putting it into the pots. Don’t press the media too much into the pot - it should be compact, but a little bit light, too.
Planting the Tubers
Tubers have an eye! From that eye the tuber will start to grow and if the tuber didn’t build a stolon by the time you want to pot it, then this eye should be potted facing up. If not, the tuber will still grow, but the new stolon have to grow around the tuber in order to reach the surface, wasting energy and nutrients. Planting the tuber in the right direction is somewhat challenging. I use a tweezers, but you have to avoid pressing the tubers too much in the process.
When the tuber is positioned correctly in the hole, fill the hole with pure sand. Don’t press the sand down- let it only trickle into the whole, so that the new stolon will not be damaged and can easily grow towards the surface.
Tuber of Drosera palladia with eye
Raising the Tubers
Now you can put the pot somewhere. If you potted tuber, which already started to grow, then put for instance with a pipette a few drops of water onto the sandy hole. If the tubers you potted did not have stolons, don’t water the pot at this stage. The residual moisture in the pot will be enough for the tuber. Until the stolon reaches the surface, the pot will not need light.
When the first green part of the plant is seen emerging from the soil, put it somewhere that suits the recommended growing conditions and start to water it. I used to adapt them slowly to more water by watering a little from the surface of the soil at first. Several days later, I used more and more water until after about two or three weeks, they were standing permanently in the water about ½ inch (1 cm) deep) until the growing period is over This is a safer method, but you may find that your tubers will be able to handle standing water immediately after budding from the surface.
How to Adapt Tubers from the Southern to the Northern Hemisphere
Because of the tilt of the earth's axis towards the sun, the seasons of the northern and southern hemisphere are reversed. When there is the summertime in down under the north Americans and Europeans are cold and when the Northern’s are having barbeque in a hot summer night the Aussies are wearing winter clothes.
Because the tuberous Drosera are heavy adapted to the climatic conditions of the southern hemisphere, they need to be acclimated to the reverse seasons if they are brought to the northern hemisphere, which can be quite challenging.
If you are getting tubers from Australia, you will usually get them from January to March and then there are three different possibilities:
1. The tubers won't sprout until the next growing season (happens rarely to never).
In this case, you’re very lucky! If the tubers remain without getting rotted or shriveled because of dehydrating and didn’t sprout, then let them remain like this. If they don’t sprout during the next autumn, then pot them and very lightly water them (dropwise!) to coax them to sprout. This is a hypothetical situation, since this has never happened to me and I never heard about it happening before.
2. The tubers start to sprout after you receive them (happens often).
This happens quite often because the internal biological clock of the tubers triggers them to start sprouting in April or May, which is the beginning of the growing season in Australia. When this happens, you need to pot the tubers as described above.
Tubers of Drosera modesta ready for planting
There are two different ways. The first is to give then a short growing period. Water them and let them grow, until they reach their full size. Let them grow for about one or two months and then stop watering. Because of the short growing season, the plant can’t collect enough energy and as a result, the tubers will be smaller than when you received them. The second is to let then grow as long as the want to grow. In the recent times I used to use the first method and right now I use the second. In both cases you can get good results.
Because of the summer temperatures, it is possible that they will start to dry out even though they are still in wet media. In this case, immediately stop watering when you see these first signs. I have lost some tubers because they've rotted at this point. Now let the pot remain like this until you see a new sprout coming out of the soil. If everything works well, this could happen when the temperatures are dropping in winter. But usually, they are a month or two later for the first or second seasons. So don’t worry if the others are emerging and the new ones are still in dormancy, possibly dreaming of flies and cold, wet weather :). If the new plant is coming out during the winter, then you've managed to adapt them to your conditions!
3. The tubers grow continuously until the next summer (happens occasionally).
If you are at the point that the tubers start to grow, you potted them, let them grow, and even if you stop watering the leaves don’t become brown, then you have 2 choices:
a. Water them again in order to let them grow the whole summer long OR
b. Wait until they will dry out
This is a difficult choice to make. Apart from some species, which are known to grow whole year long like Drosera gigantea and Drosera auriculata, I would recommend not watering them again. However, it depends on the circumstances.
4. A new tuber forms directly out of the old one (happens rarely).
Once I got a tuber of Drosera obriculata from australia. It starts to grow and a tiny stolon was visible. I potted and treated it as described above and waited and waited. After a month I could bear it no longer because nothing happened and look fort he tuber. I saw that directly under the tuber a second tuber was formed, nearly of the same size. I let the tuber in the pot with the slightly moist medium. In October I started to give a few drops of water each week and keep it at a cool place. End of December it starts to grow. Since then, it grows like the other.
Propagation Techniques for Tuberous Drosera
Propagation with Tubers
The easiest way to propagate tuberous Drosera is via tubers. This is because the only thing you'll have to worry about is meeting the conditions for good growth of mature plants, stated above. At the end of the growth period, when the above ground parts of the plants are dying, one larger tuber is usually formed along with some little, small secondary tubers.
Depending upon the species, varying amounts of small or large tubers will be formed. Three years ago I got one adult tuber of Drosera menzisii. This year, I dug out 40 tubers of different size (probably some of them were grown from seeds which fall onto the ground). On the other hand I got a tuber of Drosera obriculata. Year by year the tuber has more or less the same size, but it never formed little additional tubers and it did not flower.
Of course, the formation of additional tubers depends on how much energy the plant have. As expected, providing your plants with better conditions and feeding them regularly will increase the likelihood of obtaining material for propagation, such as seeds, offshoots, or small tubers.
Here is a small collection of tuber pictures. As you see the colour of the tubers can be quiete different.
Propagation with Seeds
Apart from tubers, seeds are the only other easy way of propagating tuberous Drosera. While it can be quite tricky to germinate some tuberous sundew species (sometimes taking over 3 years for the more difficult species), seeds have the advantage that all the resulting plants will be genetically different. If you want to obtain seeds from your tuberous Drosera, this is important to consider, since most tuberous Drosera need to be cross-pollinated with genetically different plants of the same species in order to produce seeds (or with a different species that is compatible, which will sometimes create a hybrid). If you have multiple plants that were formed from the same parent or if one plant is the off-shoot of the other, then cross-pollination will usually not work.
Drosera schmutzii with seed vessel
Germinating Tuberous Drosera Seeds
Seeds of some species needs a stratification to grow, that means that they have to be treated to simulate summer conditions so that germination occur. Seeds of Drosera macrantha, Drosera peltata and Drosera auriculata don't need stratification.
The best time so sow seeds of these species is from August to September. About one month after sowing, the average daytime temperatures should be kept under 20°C (70°F).
Keep the seeds wet and with natural (shortening) day length. Seeds will germinate when the photoperiod and the temperatures are appropriate, mainly from October to December.
Hot Stratification of Tuberous Drosera Seeds
In nature, the seeds of tuberous Drosera will remain for at least one season on the hot surface of the ground, where occasionally bush fires break out because of the hot and dry climate. It seems that nearly all species of tuberous Drosera require these hot temperatures and bush fires in order to germinate.
Again, the key to successfully cultivating of tuberous Drosera is to closely mimic the conditions tuberous Drosera are subjected to in nature.
Sow them in june and keep them dry and hot (at least about 85 °F (30 °C)) in the full sun until mid-end of September. Then keep them wet and at natural (shortening) daylight. Seeds will germinate when light period and the temperatures are appropriate, mostly from October to December. That is the easiest method and I generally use it. I sow the seeds, put a clear film onto the pot and put them onto the terrace into the full sun whole summer long.
Store the seeds from August to mid-September at around 85°F (30°C) before sowing them. Then keep them wet and at natural (shortening) daylight. Seeds will germinate when light period and the temperatures are appropriate, mostly from October to December.
Pack the seeds in some "tea-bags"-like material. I fold small envelopes out of filter paper from the coffee machine. Don’t forget to label the filter paper.
Now burn some plant debris. I use the dried parts of the tuberous Drosera, which I collect. Extinguish the fire with hot water and filter off the larger remains for instance through a coffee filter. Wait until the water has cooled down to about 140 °F (60 °C). Then put the seedsbags into the hot water for 30 to 60 seconds. You can sow the seeds right now, but it is easier to sow them when you first let them dry. Sow the seeds and keep them wet and at natural daylenght. Seeds will germinate when light period and the temperatures are appropriate, mostly from October to December. I did not try to leave the fire part out. I expect it should work as well, but that remains to be shown.
I am sure there are more options especially for bigger seeds, which usually are not so easy like D. ramellosa, D. humilis a.s.o. like soaking with GA3 (Gibberellic acid, a plant hormone that stimulate rapid root grow and increase seed germination rate) or treating them with sodium hypochlorite, but those are the ones I use and which I find quite easy to use even with larger numbers of seeds/species.
A very good guide for germinating difficult tuberous sundew seeds you can find on Dieter's homepage.
Drosera basiflora with flower and seeds vessels
Self Pollinating Tuberous Drosera
There are a few species of tuberous drosera which are known to be self pollinating and form viable seeds. Usually not all plants of a species and even not all plants of a location or of one clone are always self pollinating. Here is a picture of some of my Drosera lowriei from Holt, Western Australia. I have alltogether 9 plants from in vitro culture in the pot which are all from one plant so the plants are identically clones. I had all together 5 flowers. As you see on the picture 4 of this 5 flowers had swollen seeds vessels. Because I did not pollinate them it seems that they are self pollinating and 2 trustable growers said, that they saw the same with tubers from the same in vitro culture.
Drosera lowriei with self pollinated seed vessels.
Here is a small list of tuberous Drosera species from which is known that there are at least some clones which are self pollinating:
D. lowriei, D. planchonii, D. ramellosa, D. bicolor, D. auriculata, D. peltata, D. salina, D. stricticaulis, D. yilgarnensis.
Some species of tuberous Drosera develop "dropper roots". That are roots which are builded above the ground from the leaves or the leaf axix. They slowly grow until they reach the ground and than into the substrate. Later in the season this dropper roots sometimes build additional tubers but usually very small ones so you have to take care to find them. The known species are D. gigantea, D. intricata and D. radicans. Especially D. gigantea forms only roots when the humidity is very high (about 60 % and higher).
This is not a carrot tree ;-). Leaf of Drosera gigantea with dropper roots
There is only one species of tuberous Drosera, Drosera auriculata, with which successful leaf cuttings have been reported. I've never tried this and would not recommend it, because tuberous Drosera usually have only a few and/or small leaves in comparison to other Drosera. Plus, tuberous Drosera need the nutrients and photosynthetic products from the leaves in order to develop tubers.
It seems that root cuttings are not possible for tuberous Drosera. I've never heard about anyone doing this successfully. Therefore, I would strongly discourage taking root cuttings from tuberous Drosera, since you will probably end up harming the plant.
It seems possible to propagate tuberous drosera with stolon cuttings or better breakings. I heard at least from one trustable grower, that a stolons, which broke from a tuber by accident when he wanted to pot the tuber, grow to a new plant plus another one from the remaining tuber.
If you are interested in literature about tuberous Drosera you will always read one name: Allan Lowrie. He discovered many species of tuberous Drosera and other carnivorous plants in Australia and has published three books: Carnivorous Plants of Australia Magnum Opus Vol 1, Vol 2 and Vol 3. If someone is really interested in tuberous Drosera this three books are a must-have.
One species is named after Allan Lowrie: Drosera lowriei.
Last But Not Least
Of course, like probably anybody who grows tuberous Drosera, I am always looking for seeds and tubers of rare tuberous Drosera. If you have something more or less rare to trade please do not hesitate to contact me (Lutz).