Growing Tuberous Sundews


Tuberous sundews 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 sundews), while other species can reach over 4 feet (1,5 m) tall! Also, there are flat rosetted species that grow to 3 inches (8 cm) in diameter, in contrast to some species that develop thin, tall stems and look like a shrub!
Look here for a list of all tuberous Drosera species and their growth habit.
For more pictures, check out the growsundews tuberous photo page.

Although the cultivation of tuberous sundews 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 sundews should be your next frontier!
Drosera menziesii
Leaf of Drosera menziesii

All the herein mentioned periods, in which should be sowed, potted, repotted and harvested are relate to the northern hemisphere (see also here : How to Adapt tubers from the Southern to the Northern Hemisphere).

 

You can click on every picture on this site in order to see it in a higher resolution.


Tubers

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 menziesii
Tubers of Drosera menziesii (yes, I know, there is a white one!)

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 erythorhiza
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 pot size is 3*3 inch (7x7 cm).

Flowers

The flowers of the tuberous sundews are quite large for the size of the plant and are extraordinarily beautiful. Especially the white flowers have very pleasant-smelling honey like aromas!
  Drosera graniticolaDrosera menziesii dwarf erect form
Flowers of Drosera granticola (left) and Drosera menziesii (right), simply beautiful.

Drying out/Dessication

When the summer starts again, tuberous sundews begin to develop their tubers and their aboveground parts begin to dry out, as demonstrated in the pictures below:
Drosera macrophyllaDrosera macrophylla
Drosera macrophylla at the end of the growing season and about one month later.

Apart from brown dry tuberous Drosera can be colorful or black, too.
Drosera erythrorhiza ssp. colin dryDrosera prostratoscaposa
Dried out Drosera collina and Drosera prostratoscaposa

Climate and Habitat Information

Nearly all the tuberous sundews 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 then developing subterraneous tubers before the hot and dry summer in order to survive the dry period.
As summertime begins, temperatures begin to rise above 70 °F (20°C) 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 5 feet (1,5 m) 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 sundews grow are usually very sandy.

Average Rainfall [mm]

average rainfall
This chart is based on Perth, Australia. The original data are from the Australian Government, Bureau of Meteorology.

General Conditions for Growing

Cooler temperatures during the growing season

Tuberous sundews are picky about the temperatures. If temperatures drop below 32°F (0°C) 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.
On the other hand, if tuberous sundews receive temperatures above 75 °F (25 °C) 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 40 and 70 °F (5 to 20 °C). Mine are kept in the house at temperatures around 70 °F (20 °C) at daytime hold winter long and this works well.
In the dormancy season the temperatures should be above 70-75°F (20 °C) 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.


Average day- and nighttime temperatures

                     Fahrenheit                                                      Celsius average temperature Faverage temperature C
This chart is based on Perth, Australia. The original data are from the Australian Government, Bureau of Meteorology.

The Key to Cultivating Tuberous Sundews

The key for a successful cultivation of tuberous sundews is to closely mimic the conditions tuberous sundews are subjected to in nature. As you can see in the charts 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 sundews :).

Media Moisture

In the winter, while the tuberous sundews 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. gigantea), 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, 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.

Avoid letting your tubers rot!

The first time I grew tuberous sundews, 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 to die of thirst and not to give it even one drop of water, but they expect and need this.

Humidity

Generally tuberous sundews 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 sundews 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.

Feeding

Tuberous sundews should to be fed, too. You can follow  these guidelines for feeding.
If your plants have small leaves, it’s generally better to use very small portions. The small leaves usually have the strong tendency to die after they have digested something, regardless of if they are fed or have caught a meal by themselves. Therefore I don’t feed seedlings or small plants until they have at least 5 or more leaves.

Feeding Rosetted Tuberous Sundews

Rosetted tuberous sundews 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 with small portions of food. Especially for sundews with wide and flat leaves, like Drosera erythrorhiza, it is better to use liquid/moistened food. I prefer to feed them wingless fruit flies, since they are a very good size and their waste remains on the leaves if it is not consumed. Re-hydrated dried bloodworms also work well.
Drosera auriculata with flyDrosera erythrorhizs ssp. magna with fly
Drosera auriculata and Drosera magna with fly

Light

Like nearly all sundews, tuberous sundews 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 sundews 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 sundews. 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:

month                  08    09    10    11    12    01    02    03    04    05    06
photoperiod [h]    10    09    08    08    08    08    08    08    09    10    11

Some of the tuberous sundews 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 12 hours.
If you have the opportunity to put the tuberous sundews 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 (70 °F / 20 °C) 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 hold the time because I am afraid of loosing them, all the rest of my tuberous sundews (and pigmy and wintergrowing african sundews , too) I put to the terrace when the minimal night temperature is not less than 40 °F/5° C.


Average Hours of Sunlight (Photoperiod) [h]

Sunlight
This chart is based on Perth, Australia. The original data are from the Australian Government, Bureau of Meteorology.

How to Unpot, Collect and store tubers


Reasons for and against digging out tubers

There are good advantages for either letting the tubers remain in the pots or digging them out. I usually dig 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).
  • Sometimes the secondary tubers are all clumped together. Next time you can plant the tubers at an appropriate distance from each other.
  • In the most cases the older the plants are the deeper the tubers are formed so that the tubers are at the ground of the pot and next winter they will be under the waterline, which will probably cause them to rot.
  • If you have sown seeds and got tubers they are usually formed just below the surface, sometimes 0.2’’ (0,5 cm) and less. This area of the pot is usually the driest part and it could happen that the very little tubers are drying out and die.
  • You can be happy about the secondary tubers when they form! That’s always a bit like X-mas :)
  • Last but not least, tubers make great trading material!

On the other hand, there are good reasons to let the tubers remain in the pot:
  • 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.
  • If you use higher and wider pots the tubers will find their natural deep to form and you will not have the problem, that they are to deep in the pot
  • If you have sown seeds it could happen, that some but not all of the seeds germinate. In this case that you dig out the tubers the seeds are lost.
  • It could happen, that you did not see one or some of small secondary tubers which will be lost.
Anyway, if your collection of tuberous sundews becomes huge enough it’s simply a question of time to dig them out or not.


When and how to Collect Tubers

The important question is when to unpot tubers. The right time is about one or two 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. If it does fall apart, then it will usually still be alright. Once you have the tubers, store them according to the following directions:
  • Keep them in a dark place
  • 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 70 to 75 °F (20 to 25 °C)
  • 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.
There are good advantages for either letting the tubers remain in the pots or digging them out. I usually dig 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.
  • 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. Once someone asked me whether I dig out the roots of some African sundews, too, if they die back above the ground for the summer dormancy. Hmmm ….. that’s an argument.
Anyway, if your collection of tuberous sundews becomes huge enough it’s simply a question of time to dig them out or not.
Potting up & Planting Tubers

Pot Height - Use Tall Pots

In the literature, it is commonly mentioned that tuberous sundews 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 sundews. 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 sundews 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 sundews 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 Sundews

Tuberous sundews generally require a loose, sandy substrate. I grow nearly all my tuberous sundews 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 sundews, 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.

Black sand

Last season I used black colored sand instead of white for the sowing of the tuberous sundews 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 prostratoscaposa
Tubers of Drosera prostratoscaposa in 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:
Drosera gigantea
That are tubers of Drosera gigantea in the white sand-peat mixture. Because of the colour you can recognize them more or less well.
Here is a picture of tubers of Drosera macarantha ssp. 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 macrantha
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.

Topping

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 because of the light is a better reflected and therefore the roots are kept cooler and algae, moss etc. are discouraged, or will grow more slowly.
But later the white silica 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 zoneriaDrosera hookeri Lysterfield
           Drosera zoneria                      Drosera abberans                    Drosera hookeri

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.
Drosera tubaestylus
Tuber of drosera tubaestylus with an eye that is only slightly observable.

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.
Drosera abberans tuber
Tuber of Drosera abberans with stolon 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.

A sad story:

This winter, I got some tubers from Australia and there were 3 tubers of Drosera zoneria, too. As normal, all of them started to grow, so I potted them. Following the things I wrote above, some months later, most of the pots were totally dry apart from Drosera zoneria. These plants didn't show any sings of drying out even though I hadn't watered them for a month. Because all the other tuberous sundews standing next to this pot dried out and this one didn't, I decided to give it very small amount of water. Next winter I will write about the results. Next winter: It was hard not to cry! I lost all three tubers of D. zoneria. At the end the plant became brown, the media was nearly dry, and they were standing at a place where all the others were standing, too. In the mid of january I could not bear it anymore and carefully look for the tubers and found only three shriveled hulls. Probably the media was to dry.

Propagation Techniques for Tuberous Sundews

Propagation with tubers

The easiest way to propagate tuberous sundews 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.

Tubers of Drosera porrecta          Tubers of Drosera auriculata


Tubers of Drosera gigantea      Tubers of Drosera andersonia
Drosera zoneria Drosera zoneria
Some guys are lucky! Left is a picture of Drosera zoneria of Jean-Pierre and right the same plants short time later.


Propagation with seeds


Obtaining Seeds from your Tuberous Sundews

Apart from tubers, seeds are the only other easy way of propagating tuberous sundews. 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 sundews, this is important to consider, since most tuberous sundews 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.

Seed vessel of Drosera schmutzii
 

Germinating Tuberous Sundew 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.
Besides the photoperiod and temperature requirements in this paragraph, you can follow the seed germination guide.


Hot Stratification of Tuberous Sundew Seeds

In nature, the seeds of tuberous sundews 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 sundews require these hot temperatures and bush fires in order to germinate.
Again, the key to successfully cultivating of tuberous sundews is to closely mimic the conditions tuberous sundews are subjected to in nature.

Option 1: 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.

 

Option 2: 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.

Option 3: 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.

Option 4: 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 tuberous sundew seeds you can find on Dieter's homepage.

Drosera menziesii
Drosera menziesii var. basiflora with flower and seed vessels


Leaf Cuttings

There is only one species of tuberous sundews, Drosera auriculata, with which successful leaf cuttings have been reported. I've never tried this and would not recommend it, because tuberous sundews usually have only a few and/or small leaves in comparison to other sundews. Plus, tuberous sundews need the nutrients and photosynthetic products from the leaves in order to develop tubers.


Root Cuttings

It seems that root cuttings are not possible for tuberous sundews. I've never heard about anyone doing this successfully. Therefore, I would strongly discourage taking root cuttings from tuberous sundews, since you will probably end up harming the plant.

Stolon Cuttings

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.

Literature

If you are interested in literature about tuberous sundews you will always read one name: Allan Lowrie. He discovered many species of tuberous sundews 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 sundews this three books are a must-have.

 

One species is named after Allan Lowrie: Drosera lowriei


In 2014 a new interesting book will be published:

Drosera Of Australia And New Zealand
The books can be preordered at the Redfern natural history site.

Last but not least

Of course, like probably anybody who grows tuberous sundews, I am always looking for seeds and tubers of rare tuberous sundews. If you have something more or less rare to trade please do not hesitate to contact me.

Additional Questions or Suggestions?

Contact me at: sundewman(at)web.de