Venus Flytrap Nipped by a Winter Freeze

VIDEO TRANSCRIPT

Jacob here with Sarracenia Northwest. Since 2005, we have answered thousands of questions from carnivorous plant growers. Here’s a question from December 2020.

“I have tried to be brave and keep my plants outside, but I'm honestly afraid the cold has killed them. I'm in zone 6 and we haven't yet had snow, but the overnight temps drop below 20°F (-7°C). When I check on the plants in the morning, their (distilled) water basin and soil is completely frozen. What should I have done differently? Should I toss these poor babies in the trash and start over in the spring? For reference, the plants live by our front door on the porch where they get full sunlight all day. They are facing south. The plants have never been repotted since they were shipped to us [six months ago].”

Based on the grower’s photo, her Venus flytraps are toast. The leaves appear shriveled from dehydration, a classic sign of desiccation or frost burn. Unfortunately, there’s nothing the grower could do for them right. She’ll need to start over. On the other hand, the Sarracenia purpurea on the right still looks good. The pitchers are brightly colored and looks pretty normal for this time of the year.

The grower is in USDA zone 6, and flytraps and Sarracenia are capable of handling her winters. However, to pull it off successfully, there are some key things that needs to be done, and unfortunately, she didn’t do them in time.

But, first, let’s talk about what she did right. She said that she grew her plants in full sunlight and watered with distilled water. These are the right things to do. In her photo, I can see that her purpurea is brightly colored, and the flytraps had lots of leaves of the appropriate length. These are signs that the plants were healthy when winter started, so the grower did everything right during the growing season.

Now, there are a couple of things she could have done to prevent catastrophe. The first is prepping her plants for dormancy. The grower is in USDA zone 6. For growers in zone 6 and colder, we recommend prepping plants in November. If a grower wants to overwinter their plants outdoors, they will need to move their plants from an elevated position to the ground and mulch them with pine needles.

This is pretty standard care for all potted plants. It doesn’t matter if the plants are carnivorous or not. If a plant is in a pot and you live in zone 6 or colder, you need to mulch your plants by the end of November. The alternative is to bring plants indoors to a cold windowsill, away from heat sources and direct sunlight. This method is appropriate for growers with a small collection of plants. 

Now, I want to emphasize that it wasn’t the freezing temperatures by itself that killed her plants. At our nursery, our flytraps routinely experience overnight frosts down to 20°F (-7°C) without any protection. As long as the day temperature rose above freezing, we would leave the plants alone. We protect our plants only when the weather forecast calls for temperatures significantly below 20° (-7°C) or if temperatures are going to be below freezing for several days. In these types of conditions, potted plants risk frost burn. 

Frost burn happens when plants release moisture but can’t replace the moisture because the water in the soil is frozen. That’s what happened to the grower’s flytraps. The grower mentioned that the temperature was below 20°. At colder temperatures, there is less moisture in the air, so the risk of moisture loss increases. She also had her plants elevated, which increased their exposure to freezing wind. These conditions increase moisture loss in plants, and her flytraps have the classic appearance of frost burn.   

For growers in zone 7, 8, and 9, these types of weather conditions happen infrequently, so the only care they need to do is cover their plants. The coldest we’ve experienced here at the nursery was in December 2009 when the temperature got down to 7°F. Now, we are always monitoring the weather reports, watching for any indication of an extended freeze. When we saw the forecast for record low temperatures, we covered our plants with sheets of black plastic to shelter the them from freezing wind and minimize moisture loss. The water and pots froze solid, but the plastic sheets prevented frost burn. When the frost was over a week later, we simply uncovered the plants.

It’s possible that if the grower placed her plants on the ground and simply covered them with a bucket, her flytraps would still be alive. But, in her region, hard freezes happen frequently, so the windowsill method is simple enough. And that’s what I recommend for the grower’s surviving purpurea. She can leave the plant in the same pot, but place the pot on a cold windowsill, away from heat sources and direct sunlight.

The pot should also touch the window pane so that the plant can experience cold air. This will simulate winter in a zone 9 region. Because the plant is in a cold, stagnant environment, she should also spray the plant with a fungicide and keep the soil damp but not waterlogged. In spring, when the risk of frost has passed, she can acclimate her plant for outdoor growing.

If you want to learn more about caring for Venus flytraps and Sarracenia during winter, visit our website, growcarnivorousplants.com. We have tons of information, including our digital download, the Ultimate Carnivorous Plant Guide for Beginners. In this digital download, I share with you the precautions you need to pay attention to during winter. We also have care sheets on our website you can download for free. So, visit rowcarnivorousplants.com. Thank you so much for watching. I look forward to seeing you in another video.

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