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Dormancy in plants

Going.Local
Published on November 26th 2020
13
A cup of tea sitting on top of a wooden fence
When do plants sleep and why? It may come as a surprise to know that some species go through several months without growing. This process is commonly referred to as plant dormancy.
Plants go through a life cycle from germination to flowering and fruiting that is essentially short (annuals) or multiyear (perennials). To successfully flower, some will require extended periods of rest. So let us learn a bit more about dormancy.
caudex succulent
A large tuberous root or caudex will often indicate an adaptation to withstand droughts which can coincide with dormancy.

What is dormancy?

One definition describes dormancy as a mere period of no visible growth, but this does not always hold true. As some may have realised, diseased or dying plants will often have gone stagnant as well. Giving a sweeping statement on dormancy is not possible, because it is different in all plants (e.g. bulbs, succulents, trees). What is universal, is the fact that the plant switches off active growth on a molecular level.
A few commonly asked questions:
When do plants go dormant?
Some go dormant when winter days get shorter or summer days longer, others when the temperature rises or falls. It can also happen when a plant has finished fruiting/producing seed.
How do I know if my plant is going dormant or is sick?
It can be tricky, but it helps to know when that specific plant is supposed to start losing its leaves.
Can I make my plant grow through its dormancy period?
Sometimes you are in a hurry for your plant to get bigger and would like them to grow during a dormant period. It is not impossible if the light and temperature is maintained (subject to individual species), but will affect other parts of its life cycle, like flowering. It is generally not advised.
Should I water during dormancy?
Yes, but at a vastly lower frequency. Fungal and bacterial rot is exponentially more problematic during dormancy. You need just enough moisture to keep the roots from drying or dying. The amount will depend on your ambient temperature and humidity. Dry homes mean dry plants.
My plant started sprouting in the middle of its dormancy, what do I do?
You want to avoid this at all costs. Once they have broken dormancy you need to give them the right amount of light and temperature. Forcing them back into dormancy will negatively affect the plant.
breaking dormancy
You will know when a plant emerges from dormancy by the first signs of growth.

What triggers dormancy?

For some species, such as Lithops, they go through a summer dormancy. This means when the blistering sun and heat of summer arrives, they go dormant to conserve water. They do not need to ‘eat’ or ‘drink’ as often.
Translation | Dormancy requires you to drastically reduce water and stop fertilising.
Dormancy can be triggered by:
  • Temperature (cold or warm)
  • Daylight length (shorter vs longer)
  • Life cycle stage: Finished fruiting/flowering
Drosera sundew

Which houseplants go dormant?

Tropical plants will be accustomed to long days, temperatures that rarely change drastically and a consistent water supply. So although they do not normally go through a dormancy period in nature, they might do so in your home.
Tip | Tropical plants will slow down or completely stop growing below certain temperatures.
Some will die back to their bulbous roots and then resprout in spring.
Here are some plants that go dormant in winter:

Angel Wings

Caladium spp.

A pot of Alocasia cuprea with purple green leaves

Elephant's Ear Plant

Alocasia spp.

A pink flower on an Oxalis plant

Sorrel

Oxalis spp.

Venus flytrap

Dionaea spp.

Pitcher Plant

Sarracenia spp.

Note that dormancy may mean losing all its leaves or merely stop producing new ones.
Lithops or living stones
Lithops will go dormant in late spring and one should generally cease watering after flowering.

Dormancy in succulents

Succulents can be either summer or winter dormant. This will often coincide with the dry season in their native habitat. The diversity within each group of succulents makes it impossible to provide one guideline for a genus.
For example, Aloe come from tropical, semi-tropical, arid and semi-arid environments. Their vast diversity means some will go dormant in summer and others in winter. There is no one guideline.
Do not despair as Candide helps you in this regard by noting dormancy periods within each plant profile.
Examples of succulents that go dormant:
A plant in a garden
Elephant's foot (Dioscorea elephantipes).

Winter or summer dormant?

South Africa is one of only a few countries that experience winter, summer and year-round rainfall in separate regions of the country. Academics are currently divided on where the boundaries are, as the climate is rapidly changing. They do somewhat agree on the current division as listed below:
Summer rainfall:
  • Gauteng
  • Mpumalanga
  • Limpopo
  • North-West
  • Free State
  • (NE) Northern Cape
Winter rainfall:
  • Western Cape
  • (NW) Northern Cape
Year-round rainfall:
  • Garden Route between Mossel Bay and East London
Othonna bonsai tree
Bonsai trees will go through the same cycle and require less water during dormancy.

Important dates to remember

Regulating temperature or watering requirements can be done with ease within the home. Light is a bit more complex as few households will have access to grow lights. It will benefit you to know your solstice and equinox dates as this will help you gauge when your plants will start to wake up or go dormant.
Solstice | The longest and shortest days of the year.
  • Dec 21-22 (Longest day)
  • June 20-22 (Shortest day)
Equinox | The day the sun passes over the equator. Coincides with spring and autumn.
  • September 22-23 (1st day of Spring)
  • March 20-21 (1st day of Autumn)
You will need to start keeping an eye on the weather around the equinox. Rather wait too long than start to water too early. With changes in weather patterns, you may need to forestall spring watering for a couple of weeks till the weather stabilises. If you do start to water too early, then you might need to bring them in or provide heating in a cold spell.

Learning one new fact each day will help you enjoy your plants so much more! Learnt anything new? Let us know in the comments below.

Succulent wall
Bibliography:
Maurya, J. P., & Bhalerao, R. P. (2017). Photoperiod-and temperature-mediated control of growth cessation and dormancy in trees: a molecular perspective. Annals of botany, 120(3), 351-360.
Erez, A. (2000). Bud dormancy; phenomenon, problems and solutions in the tropics and subtropics. In Temperate fruit crops in warm climates (pp. 17-48). Springer, Dordrecht.
Chance, L. J. (2012). Cacti and succulents for cold climates: 274 outstanding species for challenging conditions. Timber Press.
Roffe, S. J., Fitchett, J. M., & Curtis, C. J. (2019). Classifying and mapping rainfall seasonality in South Africa: a review. South African Geographical Journal, 101(2), 158-174.

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