Hotbed Vs Cold Frame Choosing the Best Season Extender For Your Garden

Cold frames and hot beds are masterful tools used by gardeners to extend the season for cool-season vegetables such as spinach, kale, lettuce, green onions and beets. This publication details both construction and operation of a flue-heated hotbed while suggesting suitable soil mixture for it.

Temperature Control

Cold frames and hot beds are simple plant growth structures designed to extend gardening seasons. Utilizing solar energy, these structures help delicate plants withstand winter’s chilling temps while hardening seedlings before setting them outdoors and starting cool season crops sooner than they could in an open garden setting.

Hot beds were once heated using layers of straw-laced manure buried underneath their frames; now electric heating cables are more commonly employed.

At the core of any successful building is adequate ventilation for temperature regulation. Ventilation should take place daily, especially on sunny days, by opening up cold frames’ sashes or lifting hotbed lids to expose plants for ventilation purposes – thermometers near plants are an invaluable way to monitor ventilation levels, as are automatic venting systems that use temperature-sensitive compressed gas to move the top frame up and down automatically without using power.

Light Control

Cold frames rely on solar energy to maintain warmth, using soil and other insulating materials to trap and store heat overnight. Hotbeds utilize these same principles with additional heating sources like electric heating cables, steam or water flowing through an underground pipe or even horse or cow manure as a free source of warmth.

Both structures require careful temperature regulation and ventilation to thrive successfully, as well as being located in an ideal spot (sunny location with slope and drainage), especially on sunny days when plants could easily overheat in non-vented hotbeds or cold frames.

Standard sash frames measure three feet by six feet; wooden redwood stands up well to the elements while most gardeners opt for old windows as a more cost-effective solution. Polyethylene plastic may also work; it must, however, be treated with UV blocking material otherwise it will disintegrate under direct sunlight and cause disintegration of its own accord.

Ventilation

Hotbeds allow gardeners to extend their growing season, protect tender plants during the winter, and start cool-season crops earlier than possible in cold frames. Hotbeds are straightforward, inexpensive, and straightforward to build; but their maintenance requires consideration, especially on sunny days.

If a permanent manure hotbed is desired, dig a pit 18 to 24 inches deep and fill it with rich garden soil or compost, making sure six inches don’t pool when water is added over it. At this stage it would also be wise to install a thermostat so you can monitor soil temperatures more precisely.

An alternative electric hotbed, however, uses a frame that sits directly on the ground without needing for cinders and sand to warm itself. Preferably made of cedar lumber, its construction should accommodate standard 3′ x 6′ glass sashes banked on both sides to minimize heat loss while being controlled via single thermostat/main switch arrangement or multiple switches as illustrated in Figure 3.

Manure

Hot beds offer gardeners a means to cultivate out-of-season vegetables during early spring and late fall when temperatures prohibit open-air gardening, as well as extend harvest season crops such as beets and onions.

To build a flue-heated hot bed, begin by digging a pit 3 feet wide by 6 feet long, lining it with boards if they cannot be found in the woods, filling it with fresh manure trampled down, and banking its outside perimeter with soil or manure from your woods to block cold air currents.

Place four to five inches of good garden loam over the manure pit and cover it with glass hotbed sash for sowing purposes. Alternatively, muslin or cheesecloth may be placed over it to protect it during sowing activities. On sunny days, you must make sure the frame vents are opened regularly or else the plants will overheat and become unusable; 8-10 weeks is a general guideline when transplanting out to their fields.