How to Ventilate a Hotbed Safely

Hotbeds are plant growth structures used to protect delicate plants from frost, harden off newly transplanted seeds prior to transplanting and start cool season crops early than would occur naturally in their natural surroundings. Like cold frames, they contain heating cables.

Frost cloth or hardware cloth, a fine mesh material that provides good ventilation, should be draped over a frame. Ideally, its edges should touch the ground to help capture heat coming off the soil and act as insulation.

Ventilation Methods

Cold frames and hotbeds offer an easy solution for protecting vulnerable seedlings during the cold months, hardening off starter plants for outdoor planting, and starting cool-season crops earlier than can be accomplished in gardens. Both structures require adequate temperature control, ventilation, and watering,” according to horticulture specialist David Trinklein of University of Missouri Extension. Plants may grow on amended soil covering the floor of a frame or in containers filled with soilless media (pots or flats).

Trinklein suggests that, when creating a permanent type of manure hotbed, driving two”x 4″ cedar posts at six foot intervals along the sides and corners is preferable to nailing boards onto them. Hardware cloth nailed to each post will help protect them against mechanical injury from seedlings or soil tripping.

Trinklein recommends that when using a heating mat, it be left on all year to provide consistent warmth throughout the growing season. For optimal results, place it on a flat surface so it warms seedling pots and trays evenly.

Heat Mats

Manure hotbeds use two distinct heating elements. One is a straight or coiled resistance wire while the other is typically lead covered cable that zig-zags over the bed as shown in Figure 3. These beds may either be permanent or portable.

Manure pits should be dug during winter, when time allows. Pit depth should range between three and four feet deep and six to eight feet in length, depending on how much manure is necessary. Manure should then be forked well upon pileup to ensure no large lumps remain and that its contents have been thoroughly mixed together.

Heat mats are extremely popular among reptile breeders and come in various sizes and wattages. While heat mats may seem ideal as primary heat sources in naturalistic setups, since they only provide infrared-C which cannot effectively warm an enclosure.

Humidity Dome

Humidity domes provide a controlled environment for propagating young seedlings, minimizing water evaporation and aiding healing grafted tomato plants. Installation is simple and allows convenient control over both temperature and humidity levels.

Humidity domes can also help promote healthy mushroom growth by limiting contamination risks and supporting fruiting body formation. A filter patch within the dome allows continuous air exchange to help balance oxygen/carbon dioxide levels as well as maintain high humidity levels for optimal mushroom cultivation.

Humidification domes provide ideal conditions for rapid plant growth, speeding maturation and increasing resistance against harsher weather. They can especially benefit bonsai trees that prefer specific climates; without such artificial conditions they might not thrive as efficiently outside their preferred environments.

Additionally, humidity domes help safeguard young plants against transplant shock by creating an environment with more controllable conditions post repotting or transplanting. By limiting sudden temperature shifts and excessive sunlight exposure, humidity domes help roots recover rapidly after experiencing stressful events.

Plastic Sheets

A hotbed designed for winter use must be constructed using electrical heat; its pit should be dug to an approximate depth of eight inches and lined with washed cinders to avoid fumes when watered, followed by one inch of loose earth or compost to reduce heat loss. Once complete, place the heating element inside and cover it with hardware cloth as shown.

Throwing plastic over plants won’t work because it doesn’t provide adequate insulation and can transfer cold temperatures directly onto their leaves or stems, trapping moisture and frost on top.

Plastic sheets are flat products made of thermoplastics or thermosets such as PVC, polycarbonate and acrylic (commonly sold as Plexiglas, Acrylite or Perspex). Plastic can be produced on an industrial scale for print production or color customization with ease compared to more rigid materials like metal.