After speaking with several members here among other growers, I have realized that there are more misconceptions about successfully growing these plants than I had thought. I wrote the care sheet below last year for the NECPS members to use as a guide for their cultivation and I hope that it can help out the cp community in their efforts with this group of amazing plants. There have been some taxonomic changes to some of these species since this was written and I will amend it at a later date.
This care sheet is based on my own experience cultivating these plants indoors, under lights in a climate that's non conducive to their ease of care. Many parts of the country are far more friendly to their needs than the North East but, after some trial and error this is what works for me. Hope this can help some of you to hone your growing conditions for tuberous Drosera.
Questions, comments and critiques are welcome.
TUBEROUS DROSERA – CARE & CULTIVATION
The tuberous members of the genus Drosera are a group of highly specialized carnivorous plants comprising of approximately 70 species and sub species. All members of this group are endemic to seasonally arid areas of Australia, Tasmania, New Zealand, South East Asia and Japan. This unique group of plants represent somewhat challenging yet rewarding additions to any botanical menagerie.
Tuberous Drosera are highly adapted to live in habitats prone to extreme seasonal drought and natural bush fires. Summers in these regions are very hot and dry with little to no rainfall. In winter, temperatures fall and the rains return giving new life to these arid lands. In order to endure these adverse conditions, this group has evolved a survival strategy common to many herbaceous plants around the world, the formation of underground tubers. The main function of these tubers is to provide storage for the energy needed to sustain the plants during their long dormancy and to enable the plant to resume active growth. The formation of these tubers also allows for rapid growth once the growing season begins. Some species can grow up to 24” in several weeks after breaking dormancy and can live for 50 years.
Plants in this group can be extremely varied in appearance and growth habit. This variation is due partly to often very isolated areas of suitable micro habitats separated by vast expanses of terrain which is non-conducive to their needs. There are 4 distinct groups of tuberous Drosera which exhibit unique growth habits. These groups are as follows:
- Rosetted - The leaves of this group of plants grow on or close to the ground in a rosette pattern. Ex.- erythrorhiza, aberrans and zonaria
- Erect – This group of plants sends up a self-supporting central stalk, sometimes branching which the leaves grow off of. This group is the most diverse and includes some of the largest and smallest species. Ex. – gigantea, menziesii and microphylla
- Scrambling – Plants in this group also grow a central stalk which the leaves grow off of, however, the stalks are not as robust and depend on adjacent vegetation for support. Plants in this group can attain lengths of over 10’. Ex. – erythrogyne, macrantha
- Fan Leaved – These plants produce a relatively short central stalk often with a basal rosette. The leaves have a distinct growth pattern on short petioles. Ex. – stolonifera, ramellosa and purpurescens
Tuberous Drosera can present some challenges in cultivation mostly due to their seasonal dormancy requirements. Most species require hot, dry summers and cool, wet winters. With a thoughtful approach, these conditions are easily replicated.
Pots used for the tuberous species of Drosera should be at least 4” across and 6” deep, deeper in some species like D.gigantea and D.geniculata. Tubers should be planted, growth point or “eye” up in the top 2”-3” of soil. The tubers will often continue to work themselves deeper into the substrate and occasionally right out the drain holes in the bottom of pots so, pot depth is therefore an important aspect to consider. Some species will readily form new tubers so, make sure there is enough horizontal room in the pots to accommodate this. For example, your single D.modesta or D.menziesii could send up a miniature glistening forest the following year.
The potting media for these plants should consist of about 4 parts sand to 1 part peat. I prefer to mix a coarse grade silica sand with finer “Play Sand” but, any inert sand seems to work just fine.
These plants must be fed often while in active growth to ensure that they will have enough energy stored to sustain them through dormancy and back into an active growth cycle. The plants can be fed live or dead insects or many of the commercially available fish food pellets placed directly onto the leaves. Another method, which works well, is to spray the leaves with fertilizers such as Max Sea, Better Grow or other fertilizers made specifically for orchids. Care should be taken however not to get too much of the fertilizer onto or into the substrate as this will accelerate the growth of algae and mosses.
Photoperiod and temperature are both important factors to consider when taking on the challenge of growing tuberous Drosera. The light cycle for active growth should not exceed 10 hours of direct light. When inducing dormancy, this should be slowly increased. Temperatures should remain in the 45-70 degree range for active growth. Do not let the temperature get over 80 degrees for any length of time in winter when the plants are growing, this may trigger an early dormancy in some species. It is important to try and replicate the naturally shorter days and cool temps of winter for these plants to thrive.
Dormancy is by far the most challenging aspect to consider when growing tuberous Drosera. It must first be understood that these plants have evolved over eons to time their growth and dormancy to the natural rhythm of the seasons in their native habitat. Hot, dry summers and cool, wet winters. This cycle must be replicated in order to succeed with these plants.
Active growth will naturally begin in early to late autumn depending on species. You should start top watering the plants once per week or so starting in early to mid September. Active growth will be apparent when the plants first break the surface of the substrate a few weeks later. At this point, it is safe to place the pots in trays of shallow water for the growing season.
The plants may grow extremely rapidly in their first month of growth and some species can reach a height of 24” in only 4 weeks. They will start producing flowers shortly after reaching maximum height. Active growth will continue into the spring (or even early summer in some species). After the flowers wilt and seed is produced, the plants will start to set their clocks for summer dormancy. The light cycle should be raised gradually during this time over the course of a month or so up to at least 14 hours of day light. Temperature should also be slowly raised at this time. Pots should be removed from water trays and gradually allowed to dry out. Keep in mind that all signs of living plants will die back to the tubers and this is just their normal process.
Dormant tubers may be kept in their pots throughout the summer. Find a warm, dry spot where they can be stored for the next several months. It must be understood that that the dormant tubers (with some exceptions) must be kept bone dry for dormancy. Do not water your plants at all during this time. If tubers are left moist during dormancy, they will usually rot. During dormancy, is also the best time to repot your plants if you need to. The dormant tubers will be yellow to bright red depending on species and can vary in size from the size of a pinhead to the size of a ping pong ball so, be sure to sift through the soil carefully while looking for them. Also, as previously mentioned many species will produce additional tubers under the soil during the growing season so, be on the look out for new additions. The tubers can be carefully dug out of the substrate and safely moved, examined or shipped while dormant.
Please note that some species can deal with somewhat moist dormancy conditions and other species such as D.aberrans, D.gigantea, D.tubaestylis and similar species actually prefer some light moisture for dormancy. These species either lack the protective papery layer on the outside of the tuber or grow closer to permanent bodies of water in the wild. In the case of species like D.gigantea and D.geniculata, not only do the plants grow near permanent (or nearly permanent) bodies of water but, their tubers are often over 3' underground where the soil will stay fairly hydrated even in the midst of the dry season.
After 3-5 months of a warm, dry dormancy your plants will be ready to start the cycle anew and their seasonal processes can be repeated.
With a little bit of attentive care and some manipulation these coveted and mysterious plants can be very interesting, rewarding and often bizarre additions to your collection.
Oddballs Among Oddballs
While the majority of species within the Tuberous Drosera Group can be grown fairly standardly by using the above mentioned methods, there are a few exceptions.
There are 2 annual species which are placed within this group of plants. D.banksii and D.subtilis grow in the tropical Northern Territories of Australia and do not produce tubers ! Instead these species are both annuals, dying and growing new plants from seed produced the previous year on an annual basis. These 2 species should be grown more like the plants in the D.petiolaris complex with hot, humid summers and dryer winters. Seed should be collected and stored for later germination attempts as these plants will not survive normal dormancy practices.
Another exception to the rules of Tuberous Drosera cultivation are the more Northern forms of D.lunata, such as the plants from Japan. These plants, rather than being winter growing/summer dormant are completely the opposite, being dormant in winter and resuming active growth during the spring and summer months. This plant has found it's way to the warm temperate parts of Japan and has adapted to suit this climate. Being a similar climate to most parts of the Carolinas in the U.S., winters here are too cold to support active growth in the winter months so the plant has switched it's growth cycles to coincide with a more conducive season for growing.
Acclimation Of Imported Tubers
These plants, while becoming increasingly common in collections in the United States are still quite rare and can be difficult to obtain domestically. Often the best place to purchase these plants is from growers in their native Australia. This however presents a new hurdle in their care. Being in the Southern Hemisphere, Australia’s seasons are in reverse from our own. Their winter is our summer. So, what does this mean for your newly imported tubers from Australia ? It means the dormant tubers will need to be tricked into resetting their internal clocks to be able to grow in the Northern Hemisphere. This can sometimes be a delicate process resulting in losses due to rot.
Australian grown tubers are usually available from December to February, their summer. When your tubers arrive in our winter they will be fully dormant. Place your newly arrived tubers in sandwich sized zip lock baggies with a piece of dry paper towel or a sprig of long frond sphagnum moss. The paper towel or moss will help absorb any ambient humidity or moisture that may foul the tubers and cause them to rot while in the plastic bags. Place the baggies containing the tubers in a cool, dark area such as a drawer in a cooler area of the house or a dry corner of the basement. Check on the tubers regularly, once every week or so.
After several weeks of being exposed to cooler temperatures, you will start to see the first signs that the ruse has begun to work. Signs of life will start to become apparent from the eye or growth point of the tuber. This is the plants stolon starting its upward migration through the soil to the surface. The tubers should be planted in their pots after there is at least a half an inch of stolon emerging from the tuber. Plant the tubers 2” to 3” into the soil. They should also be top watered regularly at this time and allowed to drain. Once you observe the plants breaking through the soil surface at the top of the pot you can place the pots in trays of shallow water.
From this point, the plants will need a shortened growing season. They will need to be fed heavily during this time. The extra energy will be needed for them to survive being rushed through a year of growth in just a few short months. Remove the plants from their water trays in late June to mid July, by this time our summer heat will already be forcing them into an early dormancy. Keep the pots containing the tubers warm and completely dry until fall. By mid to late October the plants should be starting to grow again, now becoming in tune with our seasons.
Growing Tuberous Drosera From Seed
Tuberous Drosera seed is commonly available, unfortunately some species can be extremely difficult to grow from seed. The first thing to understand with growing these plants from seed is timing. Reguardless of species, seed from the previous year should be sown in late summer or early fall. I do not recommend storing seed from Tuberous Drosera in the refrigerator as you would for many other Drosera species. Instead, store them in a warm, dry place until late summer/early fall. Species in the D.peltata and D.macrantha complexes can just be sown in late summer with no special treatment. I've had plants in these groups reach adult, flowering size in only a single season. Many other species will need a hot, dry stratification over the summer in order to germinate. Some species with exceptionally large and tough seed coats such as D.lowriei or D.ramellosa can be extremely difficult to germinate. These species will need a hot, dry stratification combined with other, somewhat experimental treatments for the seeds to sprout. Photoperiod is also thought to play a hand in germination, the seeds will sit dormant until light levels have dropped to appropriate levels. Only when the light cycle has dropped signifigantly will the seeds start to sprout. Also keep in mind that without additional treatments to encourage germination, seeds of many species can take several years to germinate. Listed below are some additional methods and tricks used by myself and other growers to initiate germination.
GA3 (Gibberellic Acid)
Treating seeds with GA3 is probably the most common method used to sprout difficult to germinate seed. GA3 is a powerful hormone naturally found in small amounts in plants. This hormone promotes the growth of plant cells and controls growth rate in plants and fungi. Seeds should be soaked in a GA3 solution for no more than 24 hours prior to sowing.
From first hand experience, I can vouch that these treatment work well for some species. There are various ways to achieve this. The first and most basic way is to sow the seeds on their perferred media and build a small, fast burning grass fire on top of them. However, lighting small fires comes with a list of potential complications that I don't think I need to go into detail about here. It has been proven that it's the chemicals in the smoke (butenolides and various nitrates among them) and not the flames/heat that actually stimulate the seeds to sprout. Sprinkling small amounts of plant based ash over the seeds, soaking the seeds over night with a smoke disc (pre-smoked filter paper) and even Liquid Smoke sold in grocery stores to add a smoky flavor to food will all have some degree of benefit. I have also used a smoking gun made for the culinary industry to cold smoke seeds with success.
Sodium Hypochlorite (Bleach) Treatments
Soaking the seeds of very difficult to germinate species with large, tough seeds (D.lowriei, D.ramellosa etc..) in a weak 2% - 2.5% solution of Household Bleach and warm water has also proven to work. Seeds should be folded into paper towels or coffee filters, then submerged in the solution for no more than 15 to 20 minutes. Seeds must be thoroughly washed after treatment to remove all traces of bleach. I prefer to unwrap the seeds from the paper towel or coffee filter after removal from the solution and drop them into a large jar of clean water, swish them around vigorously then remove them with a pipette and place them onto the germination media.
Here are some plants from my own collection grown using these methods.
Drosera auriculata - Seedlings
Drosera gigantea tubers
Drosera porrecta - Northern Form
Drosera squamosa - Laterite Growing Form
Drosera squamosa - Sand Growing Form
Drosera zonaria "Large Form"