The Christmas cactus sports vibrant flowers in shades of red, pink, orange, and lavender and lights up your home when everything else is blanketed in snow. We would all love to have a stunning floral display in our homes just in time for the holidays, but sometimes, you can only coax your cactus to bloom by Christmas by putting it in the dark.
You put a Christmas cactus in the dark to induce a dormancy stage and force it to flower. During this period of darkness, the cactus conserves its energy and undergoes hormonal changes to prepare for setting buds when you move it to light and induce it to emerge from its dormancy.
To make your Christmas cactus flower when you want, you have to mimic its life cycle in its natural habitat and force it to go into dormancy. It helps if you understand why the Christmas cactus needs darkness to bloom and how to make it go dormant. I’ll explain these fascinating physiological processes in this article and describe how you can create the ideal flowering conditions for your Christmas cactus.
The Necessity of Darkness for Flower Initiation
Plants need total darkness to metabolize efficiently. Plants photosynthesize during the day and produce food, but they cannot go on producing food indefinitely. They need a period of darkness to use the stored food to rest, regenerate, grow, and get ready to produce fruits and flowers.
Shrubs, plants, and trees need a period of total darkness to produce phytochrome.
Phytochrome is a crucial compound that lets plants keep track of the seasons and determine when to produce buds, bloom, shed their leaves in the fall, and set seeds. This process is known as photoperiodism, and plants regulate it by making the hormone phytochrome.
Not getting enough darkness or being exposed to even the tiniest amount of light during nighttime can hamper the process of photoperiodism.
Photoperiodism is regulated when phytochrome 730 slowly transforms into phytochrome 660 at night. The more the hours of darkness, the greater the amount of phytochrome 660 produced.
So, what do all these physiological processes mean for your Christmas cactus?
The Christmas cactus is a “short-day” plant.
Short-day plants do not bloom till the days are shorter than a specific length, which could be around 15½ hours for some plants. Phytochrome 730 acts as a bloom inhibitor in short-day plants.
To set buds, short-day plants need phytochrome 660, produced only in the dark. So, plants like the Christmas cactus need an uninterrupted period of darkness to flower.
Plants have evolved to thrive in a specific day and night cycle. They carry out the various physiological processes needed to survive, set buds, and produce seeds using phytochrome to respond to these cycles.
You need to mimic these natural conditions to make your Christmas cactus flower.
Timing the Darkness
You should put your Christmas cactus in the dark around late September or October and no later than early November if you want it to bloom during Christmas. The rule of thumb is to put your cactus in the dark for at least six to eight weeks before you want it to bloom.
Unlike other succulents, the Christmas cactus can bloom multiple times a year. You can make it bloom in spring or during Thanksgiving by ensuring it receives abundant light during the day and 12-14 hours of darkness every day for at least six to eight weeks before you want the buds to appear.
Regulating Light, Temperature, and Water
The trick to forcing Christmas cactus to bloom is to regulate these three factors: light, temperature, and water.
Christmas cactus blooms after it goes through a period of dormancy in a cool and dark environment.
Almost all plants need a period of dormancy to survive harsh weather periods and regenerate and regrow year after year. Plants usually naturally enter a state of dormancy as winter approaches.
A period of dormancy slows down the growth rate of plants and lets them conserve energy. This period infuses plants with renewed vigor to bear flowers when the weather turns warmer. The plants can produce more prominent and more vibrant flowers with renewed energy.
Read on as I explain how you can regulate light, temperature, and water to create the right environment to induce dormancy in your Christmas cactus.
Create the Ideal Dark Environment
Shorter days and longer nights signal the arrival of winter when the Christmas cactus naturally enters a period of dormancy.
However, if you want to force it to flower during the holiday season or live in a region where the winters are mild and the nights aren’t too long, you must create the ideal period of darkness for your Christmas cactus.
How Long Should the Period of Total Darkness Be?
You should keep a Christmas cactus in the dark for about 12-14 hours every day for at least 6 to 8 weeks to encourage buds. This should be a period of total darkness. You must not turn on artificial lights even for a short while during this period to avoid disrupting the dark cycle.
You can place your Christmas cactus inside a dark closet or a box to create total darkness. You can also wrap the plant in layers of paper or a breathable piece of fabric to cut off the light.
If you place your Christmas cactus in a room, ensure that nobody turns on the lights once the sun sets. You must also ensure that lamps from the yard or street do not filter into the room through the curtains.
You should place your Christmas cactus at a temperature between 50 and 55 °F (10 and 13 °C). You may have to find a cool place in your house or turn the heater down to create a cool environment.
During the day, ensure that you place the plant where it receives indirect light. An east-facing window is an ideal spot.
You have to find a spot in your home that fulfills both the light and temperature requirements.
Unlike other succulents, the Christmas cactus needs slightly more watering to survive.
Although the Christmas cactus stores some water in its leaves, it is not as efficient at the job as the spiny desert cacti varieties. It tends to drop its foliage and droop if it goes too long without water.
However, you have to cut down on the watering to induce it to go into a period of dormancy.
The following are the tips to create the proper watering schedule to induce dormancy:
- Start reducing the amount of water you give to your plant from late September or early October.
- Water only the topmost layer, about 1 inch (2.5 cm), of the soil.
- Ensure that you only lightly moisten the soil.
- Water only when the soil feels dry to the touch.
- Ensure the potting mix is well-draining.
- Ensure there are drainage holes at the bottom of the pot.
- Don’t let the plant sit in water. Otherwise, its roots will rot.
The Christmas cactus flowers about 4-12 weeks after the buds appear.
You should relocate the plant to a sunny and warmer spot when the buds appear. However, keep it away from direct sunlight.
The Christmas cactus is a forest cactus. It grows in tropical forests, shaded by the canopy of the trees, and receives dappled sunlight. The Christmas cactus tends to wilt under the sun’s harsh rays, unlike its desert cousins.
You can place the plant near a south- or west-facing window, but make sure that there are curtains to filter in the sunlight.
You must also protect the newly-formed buds by placing the plant away from hot or cold air drafts. The tender buds will fall off if the plant is in stiff breezes or high temperatures. Keep the plant where the nighttime temperature is around 55 °F (13 C).
Increase water uptake by deeply watering the plant, but make sure to drain out the excess water on the pot. Don’t let water accumulate in the saucer under the pot. Newly-formed buds can fall off if you overwater the plant.
The Christmas cactus loves humidity. However, it tends to be drier inside our homes than outside in winter. The air is almost always drier if you use a heater.
So, create a humid environment for your plant by keeping the pot on a tray of pebbles and water. You can also group your cactus along with other plants.
Don’t move your cactus to a larger pot unless you think its roots are outgrowing its present planter. Christmas cactus loves to be root-bound and produces more flowers when the roots are in a cramped place.
Did you know that most cactus flowers only last for a day? Learn why in my post: Why Do Cactus Flowers Only Last for a Day?
The Christmas cactus is a robust plant that lives for decades if you care for it properly. It is a low-maintenance plant.
However, you must understand how the plant behaves in its natural habitat if you want to enjoy its blooms during the holiday season or make it flower multiple times. Most importantly, you must understand how to mimic the cool and dark conditions that induce it to flower.
Keep in mind that the Christmas cactus needs to be in absolute, total darkness for 12-14 hours for six to eight weeks before it will set buds.