Expert: Christopher Littrell - 9/23/2007

Question
Hi, I have two venus flytraps and a primrose butterwort.  It's nearing the time for them to go into dormancy.  I have only been growing carnivorous plants for a couple of months.  What should I do for these plants for dormancy?

Answer
Hello Dave,

Both of those plants are close enough in zone to give them the same dormancy conditions.

If the plants are outside or in a window, they will receive signs of impending winter from the lessening photoperiod if you live in North America. Dormancy will be triggered by drops in temperature down to about 45 degrees after the photoperiod changes. Both plants can survive short temperatures into the 20-30 range in Fahrenheit, however; since they are in pots they are not as insulated, so protect them in an unheated garage or under a tarp if they are outside in the coldest days. Best bet is to keep them about 40-50 degrees through winter.

If you are unable to keep the plants outdoors or in a cold room and you are growing them under artificial light, you will need to lessen the hour photoperiod by one hour per week in November until the plants get 8 hours a day, then simulate frost by either placing the plants near a cold window or in a cold room, or placing them in the refrigerator, not the freezer, or in an ice chest with ice water bottles around the pots. Use a thermometer to ensure the temperature gets down to around 45 degrees in the ice chest. Some people just leave their plants in the fridge all winter in plastic ziplock bags slightly open to allow air in. In February, get them out of cold conditions and begin giving ythem light for 8 hours a day, ramping the light up by one hour a week until they get 12 or more hours a day again. If they can be placed in a sunny window or outside, they will react to natural spring conditions and come out of dormancy without all the hard work on your part.

Water the plants about half as much as you normally would while they are dormant. They still need to have their soil barely moist and only a slight amount of water in the tray, but keep the water level down to reduce root rot while the plants are inactive.

If you opt for the refrigerator method, keep vigilant for mold and spray the plants with neem oil or sulfur based fungicides should you see any fungus growing on or around the plants. Fungus is a main killer of dormant plants in the refrigerator or inside in stagnant, dark conditions.

If you opt for the ice chest, you can go an extra mile by opening the ice chest for 8 hours a day and placing it about a foot or more from light. This will air out the ice chest and allow some light in to reduce the incidence of mold. Use that time to inspect the plants for mold and water them as needed. Replace ice bottles every 12 hours to keep the conditions cold in the chest. When open in the day, the ice bottles will keep the chest at about 50 degrees, which is fine.

In any case, if you have to simulate dormancy ensure that photoperiod changes occur first before you place the plants in cold conditions or they will not have a chance to produce winter hormones to keep their cells alive. In spring, take them out of cold conditions first then increase the photoperiod when you take them out of dormancy.

Clearly outside growing is easier and produces healthier plants in the long run if you are able to do so. If not, just be vigilant for fungus and signs of plant deterioration.

Christopher