Home      Dormancy In The Tropics
 
 
 
Some years ago I was asked to contribute an article to a local forum about CP dormancy in the tropics (the original article can be found here). In this article I will be dealing with similar points but with some refinements, and also a section on hot dormancy after experimenting with a generous selection of tuberous Drosera that Allen Lowrie had very kindly contributed for my experiments.

A large number of CPs are found in places that experience season variations in nature. During the inhospitable periods (winter in the northern hemisphere or the hot dry summers of Australia) CPs have evolved to take a rest in growing and enter a state of arrested growth called dormancy.

Winter Dormancy
This first section deals with winter dormancy, where plants are triggered by shortening daylength, reduced rainfall and decreasing temperatures to enter dormancy. Winter dormancy is a bit of a challenge in tropical Singapore, where our temperatures, daylength and rainfall stays near constant year round. If you're growing plants that require a winter dormancy, these plants will need a mandatory rest once a year, or you will risk them going into exhaustion and eventually wasting away. This list is by no means comprehensive (there are always exceptions even within the same genus), but these are some of the plants that experience a winter dormancy:
  • Darlingtonia californica
  • Dionaea muscipula
  • Temperature Drosera (D.rotundifolia, D.linearis, D.anglica etc)
  • Temperate Pinguicula (P.grandiflora, P.corsica, P.vulgaris, P.poldinii etc)
  • All Sarracenia species and hybrids
  • Certain aquatic Utricularia such as U.macrarhiza, but I have not had enough experience or heard enough to gauge if a winter rest period is mandatory for them

Most of my experiences are based on D.muscipula and Sarracenia, as I hardly grow any Pinguicula (I swear, these pretty little plants hate me) and I simply make vegetative propagations for the temperate Drosera on an annual basis to keep them going.

I have made some observations through the years on what stimulates dormancy in plants when grown in tropical environments here in Singapore. Very often, I would find that certain plants such as Dionaea and some Sarracenia will enter dormancy without any additional help, and hold back on their rate of growth. This tends to occur around December to January. Our daylength remains almost constant all year round, as Singapore is just 1 degree north of the equator. Yet, something else must be at play to trigger these plants into dormancy. To understand this better, we will need to consult the following weather conditions in Singapore:
 
Chart data based on NEA's weather statistics

Although daylength remains the same, the Northeast monsoon period from Dec to early March results in a large number of days of precipitation, often lasting more than a day each. As to be expected during rainy months, temperatures in Dec and Jan dip very slightly, but that 1 or 2-degree mean drop will probably not affect the plants to any degree. My own hypothesis is that the extensive cloud cover and hence lower sunlight intensity during these months may trigger them into going dormant. 
 
Given that these plants do receive at least some amount of dormancy trigger due to the weather, it will be useful to be able to recognise these signs early so that adjustments can be made to help them into dormancy. These are the clues that I have observed:

1. Decreased rate of growth
2. Serially decreasing size of leaves/traps
3. Form
Dionaea will produce smaller leaves that are more ground-hugging with wider petioles and smaller traps while some temperate Drosera and Pinguicula will form a tightly-formed central area called a hibernicula. Some Sarracenia such as S.oreophila, S.flava and certain of their hybrids will form thin, non-carnivorous modified traps called phyllodia.
 
Dionaea muscipula "Shark's Teeth" in active summer growth. Most varieties of VFT exhibit vertical petioles during active growth, although there are a few exceptions that produce prostate growth such as "Fine Tooth X Red".
The exact same plant, entering dormancy. Note that the leaves have become ground-hugging, with widened petioles and smaller traps. This plant produces one leaf a week on average, but nearer dormancy growth slows considerably to a leaf every 2-3 weeks.
An example of a prostrate VFT form going into dormancy ("Fine Tooth x Red" in this instance). These are a little more difficult to gauge as their leaves are ground-hugging even during active growth, but what is evident here is the progressively smaller leaves and trap size. 
 
By the way, ignore the coconut-fibre pots. These were a complete fiasco (I had an idea that they may keep the roots cooler), as they disintegrated completely before a single growth season was up. 

Poor growth, combined with small non-functional phyllodia heralds the start of dormancy for this Sarracenia.
 


It is important to keep in mind that it is a constellation of signs, rather than any one of the above, that are suggestive of the beginning of dormancy. In other words, the plant should have been growing happily prior to these events happening, and you are fairly certain that the poor growth or small leaves are not simply the result of a new, suboptimal growing condition such as poor lighting or pests.    
 
This plant may be easily mistaken as going into dormancy, with it's widened petioles. However, it is still in active growth, putting up large numbers of traps each week.It's simply not receiving adequate sunlight, which explains the enlarged yet etiolated petioles, and greenish trap interiors. 
                                        

Once I'm fairly confident that the plant in question is indeed going into dormancy, I usually prep them for a period of rest. This serves to reinforce the signals of an impending dormant period for the plant, and also perhaps to ameliorate any shock that they may experience. Gradually cut down on watering, so that the plant dries out between waterings. I also gradually wean down the photoperiod by placing them in a shadier location. This pre-treatment is done for 1 to 2 weeks before proceeding to dormancy proper.

I have tried 2 methods of maintaining a dormant state in CPs, and both have their equal merits and difficulties. The first one is a fridge dormancy, where the plants are placed into the crisper compartment of the fridge for 6-12 weeks. These are the steps I use to do this:

1. Unpot the plant, and gently tease off any excess media.
2. Trim any dead leaves down to the base, and old roots may also be trimmed off.
3. Wrap the root ball in some damp live sphagnum moss. This is followed by a light misting of Captan or other fungicide.
4. Place the entire plant in a breathable plastic bag (with holes punched in it), tie it securely and place in the fridge.
5. Inspect the plants once every 2 weeks or so, keeping the substrate just very barely damp and not wet. I also take this time to trim away any leaves that have died down over time, and a repeat application of fungicide is also done every month.
6. Alternatively if you have the luxury of space or a dedicated fridge for plants, it might be a better idea to just wrap the entire pot, plant and all, in a bag and leave it in the fridge.
 
Regarding the actual length of dormancy, I have not come across any literature stating specifically how long it should be. In their natural habitat most go through about 3 months of dormancy, but I tend to play by ear (or more appropriately, by eye). They are all allowed a minimum of 6 weeks in their dormant state (8 weeks for the more northern plants such as Sarracenia purpurea and Drosera rotundifolia), and during my fortnightly checks for those in the fridge I look out for signs of distress or disease.
 
Fortnightly checks are done for the plants in fridge dormancy, inspecting the rhizome and growing point for signs of fungus or stress. Dead growth which occurs in dormancy are pulled off to discourage fungal growth, and the Sphagnum is inspected to ensure that it remains damp. 
 

7. Once the 6-12 weeks of dormancy are up, take them out of the fridge and allow them to settle slowly to room temperate. Subsequently, repot the plants in new medium.
8. Instead of returning the plants directly to the tray system, I initially place them somewhere shadier and for a week or two I allow the tray to dry out between waterings.
9. Return to the tray watering method, wait for new growth and flowers to appear.
 
I have read with interest on some forums where growers in temperate countries have plants that break dormancy during the occasional warmer spell at the end of winter, which brings up the possibility of further refining this fridge technique to make it closer to what the plants experience in nature. Although the vast majority of the mortality I get is during the dormant period itself (drying out i.e. carelessness, or to fungus and rot), I have noticed that a small number of plants do go into shock after being planted out and succumb to rot. This is particularly true for those that I returned directly to the tray watering system without gradually increasing their sun exposure and watering amount. At the time of writing this article, I have a batch of 10 Sarracenia plants that have been lying dormant in the fridge for the last 4 weeks. I plan to attempt a week or 2 of dormancy-breaking simulation for this batch by bringing them out for a touch of (indirect) sunlight and warmer temperatures for half an hour each day, and will update this page on any improvements subsequently. 
 
 Flytraps that are exhibiting signs of impending dormancy, dug up and ready to go into the fridge. 
First they are trimmed of all dead growth and excess roots, leaving only a small amount of viable roots and the underground bulb. These are dipped briefly in fungicide.
Some of the healthier traps are left on for the larger plants, and they are placed into fenestrated bags on a bed of moist sphagnum which has been soaked in fungicide.
A top dressing of more moist sphagnum is added. Nowadays I use live sphagnum, which supposedly has antifungal properties of its own, but I still soak the live sphagnum in fungicide nonetheless. 
Finally, the end of dormancy. Note how the sphagnum is kept just barely moist. The plants will still grow during their dormant period, albeit awfully slowly especially at the end of their dormant period. See how the new season's leaves compare to the wide petioles from the previous season. 


I have also tried a "dry" method of maintaining dormancy that does not involve the fridge. This method is by no means close to what the plants experience in nature, but it probably works by simulating a couple of things: an adverse growing condition to trigger/maintain dormancy, and providing just enough water so that the plants do not dehydrate but yet discourage fungal growth.
 
To do this:

1. Trim off any dead leaves down to the base
2. Place the entire pot in a shady place, and water sparingly such that the substrate if just barely damp
3. Once 4-8 weeks are up, gradually move them out to a brighter location and increase watering gradually.

So far the plants seem to do well using both methods, and some of my flytraps have been going on for years using the dry method exclusively - this is especially true for those on the balcony, as I have to do some pretty nifty acrobatics to access the plants and subsequently the fridge (path of least resistance ...) For the bulk of my plants in the garden, I tend to use the cold dormancy method as I have an extra fridge to place the plants in, and sometimes well-meaning family members mistake the dormant plants for sadistic abuse neglect and plonk them back onto the water trays. In addition, it seems a little closer to what the plants go through in their natural environment - more physiological, if you will. Still, the dry method works for most plants such as Dionaea and Sarracenia here in our climate, and you don't need to waste a night on explanations to your spouse on why those pots are in the fridge. 

Summer Dormancy
Some plants experience inhospitable climate elements at the peak of summer, where water becomes scarce and days become hot. To adapt, they go into a period of dormancy in summer, either by forming tubers or modified compact leaves. Most of these species come from Australia, such as tuberous Drosera, pygmy Drosera and Drosera from the petiolaris complex. My own experience with tuberous Drosera and pygmy Drosera is very limited, and so far have only been able to keep D.peltata happy in cultivation outdoors. Drosera from the petiolaris complex fare much better and are easier to keep happy here. Most of the year they will go into rapid growth, but once in a while especially in the hot months, the petiolaris complex Drosera will start sending out leaves with significantly smaller traps, and the entire plant adopts a compact growth form. Once this happens I take them off the tray to prevent rot but still in a bright sunny spot, and water daily so that the substrate remains damp. When they restart on rapid growth again, I simply place them back onto the tray watering method.
 
 Drosera fulva starting to go into its summer dormancy, with smaller rosettes of leaves and traps.