In The Greenhouse This December

Maintain Temperature and Humidity Levels

• Monitor Temperature: The primary concern in December is maintaining a consistent temperature inside the greenhouse. Use a thermometer to keep an eye on the temperature and consider adding a heater if necessary, especially during very cold spells.
• Ventilation: Even though it’s cold outside, ensure there is some air circulation to prevent humidity from building up and to prevent fungal diseases. Open vents or use fans to ensure airflow when the weather permits.
• Humidity Control: Winter air is often very dry, especially when heating is used. If humidity becomes too low, consider using a humidity tray (a shallow pan with water) or a small humidifier to help maintain moisture in the air. However, ensure that there is not excessive moisture buildup, as that can lead to mold and mildew.

Keep Plants Protected from Cold

• Insulate the Greenhouse: Make sure the greenhouse is well-insulated to help retain heat. Consider adding extra layers of bubble wrap or thermal blankets to the inside of the greenhouse if you have not done so already. These can help improve insulation without blocking too much light.
• Frost Protection: If you have any frost-sensitive plants inside, use horticultural fleece or row covers to protect them. You can also group plants together to conserve heat, as the warmth from one plant can help the others.

Watering Carefully

• Watering Needs: Be cautious with watering in December. Many plants in the greenhouse will be dormant or growing very slowly, so they will not require as much water. Check the soil moisture regularly, and water only when the soil feels dry to the touch. Overwatering can lead to mold and root rot, especially in cooler conditions.
• Water in the Morning: If you need to water, try to do so in the morning, so the plants have time to dry out during the day. Watering in the evening can lead to increased humidity and potential fungal growth.

Harvest Winter Crops

• Harvesting: If you’re growing winter vegetables or herbs (such as lettuce, spinach, kale, or herbs like parsley and cilantro), continue to harvest them throughout the month. These plants can continue growing in the mild temperatures of the greenhouse.
• Forcing Early Crops: If you’ve planted crops like early spring peas, lettuce, or radishes in your greenhouse, they may start to mature now. You can harvest these for an early crop in the winter.

Clean and Maintain the Greenhouse

• Clean Surfaces and Equipment: Clean the inside of the greenhouse, including the glass or plastic panels, shelves, pots, and trays. Removing dirt and debris will allow more light to enter the greenhouse and reduce the risk of pests and diseases. Clean and disinfect any tools or equipment that will be used in the greenhouse in the coming months.
• Inspect for Pests: Even in winter, pests can find their way into the greenhouse. Keep an eye out for aphids, whiteflies, and spider mites. If you notice any, take action immediately.

Manage Light Levels

• Provide Supplemental Lighting: December’s shorter days mean there may not be enough natural light for plants to grow well. Consider adding supplemental lighting if your greenhouse plants require more light to thrive. Fluorescent or LED grow lights are good options for providing the right spectrum of light.

Monitor and Maintain Greenhouse Structure

• Check for Leaks or Damage: Ensure that there are no cracks or leaks in the greenhouse that could let in cold air or moisture. Check the structure for any signs of wear or damage from storms or snow buildup. Make repairs as needed.

By following these tips, you’ll help ensure your greenhouse is a productive and healthy environment for plants throughout December and ready for an early start to the growing season in the new year.