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Spirekassen

29 Nov 2023 09:38

Winter Cultivation and Frost

 

This article is for those who love geeky information presented in an understandable language. You'll briefly learn about plant cell structure and, specifically, what distinguishes plants that can be cultivated during winter from those that can only be cultivated during summer.

If you've discovered the joy of winter cultivation, you're probably eager to fill pots and containers with plants in the fall. There's nothing as delightful as having a green oasis in your greenhouse, even during the winter.

It's November and experiencing frost at this time of year is quite normal. We've learned from our Spirekassen customers that the first frost can be a cause for concern for many.

At the beginning of October, you likely have many thriving plants, including various types of cabbage, spinach, salads, hardy herbs, and leaf beets.

The question is, "will my winter cultivation perish in the greenhouse when frost arrives?"

The answer is "no."

Plants we cultivate during winter can withstand frost because they possess a few clever survival mechanisms.

 

Plant Cell Structure

Humans and plants have many things in common, including our building blocks— the cells. However, there are distinct differences. Plant cells are encased in a rigid cellulose structure, which is familiar to paper and wood. Unlike human cells, plant cells contain chlorophyll granules, specifically in the chloroplasts, where photosynthesis takes place. Different types of cells serve various functions in the plant.

Key Concepts

Within the plant cell, there is a large water-filled bubble called a vacuole, contributing to turgor pressure, which helps support our greenhouse plants. When turgor pressure in plant cells decreases, the plants start to wilt, signalling the need for water to restore turgor pressure. This is a clever strategy. Plants that wilt due to water deficiency quickly reduce their leaf area, leading to reduced water evaporation. This allows them to survive temporary drought conditions.

 

Similarities with Winter Cultivation

We experience something similar when our winter-cultivated plants face frost. You may have noticed your plants wilting when the temperature drops below freezing point. This is due to a disruption in turgor pressure within the plant cells, which helps prevent frost damage.

Our winter cultivation is unique because many greenhouse plants are herbaceous and consist of roughly 90% water. When summer greenhouse plants experience frost, the water in their cells freezes, leading to ice crystal formation and cell damage. We've all likely seen this when the first frost kills tomato and cucumber plants.

During winter, we can cultivate specific plants in the greenhouse, such as cabbage, leaf chicory, Swiss chard, and certain herbs. To succeed in winter cultivation, it's crucial to gradually acclimate plants to the cold. You shouldn't pre-germinate your cabbage on the windowsill in November and place it directly in the greenhouse, as it will not survive.

 

The Magical World of Plant Cells

Winter-cultivated plants that can endure frost have several mechanisms to avoid frost damage. Water behaves differently in their smaller plant cells compared to what we're used to. These plant cells can be organized differently to prevent water from freezing and forming ice crystals. All green plants produce sugar through photosynthesis. Sugar functions similarly to salt on icy roads; it lowers the freezing point of water, allowing it to remain in a liquid state even at temperatures as low as -20 degrees Celsius. This protects the plants from frost damage.

Another strategy plants employ to protect themselves from frost is to remove water from their cells, causing it to freeze between the cells without harming the plant cells. However, prolonged exposure to frost using this method can stress the plant, potentially leading to cellular damage, even in cold conditions when the plant isn't losing moisture from its leaves.

 

Helpful Tips
  • Pre-germinating plants for winter cultivation should be done in an unheated greenhouse.
  • Start your winter cultivation early, preferably in late August.
  • Don't be disheartened if your winter cultivation appears to wither in frosty weather; it's a temporary loss of turgor pressure.
  • When temperatures rise above freezing, turgor pressure will be restored.
  • Harvest your winter cultivation only when the temperature is above freezing point.

 

Thank you for sharing your knowledge, Bent Løschenkohl (Hortonom).

Om Spirekassen

Christine Wiemann is a greenhouse grower and an agricultural technician and owner of the seed company Spirekassen. Christine is an author of several books about lifestyle, garden life and plant cultivation. Today she writes blogs and shares her knowledge and passion for greenhouses. Christine is a greenhouse expert and an ambassador for Juliana Drivhuse.

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