ELECTRIC HOTBED FOR PLANTS

OBJECTIVE:

To heat soil for earlier and more uniform seed germination for early plant production.

SKILLS:

Participation in 4-H Horticulture program; Wiring

TIME:    Approximately 1 hour

INSTRUCTOR NEEDS:

Volunteer Leader per class of twenty participants

PARTS LIST:
Metal baking pan 10" x 18" or larger with a minimum depth of 2"
110-volt heating cable to provide 10 watts of heating per square foot of pan surface
Thermostat with an operating range 30 to 120 Fahrenheit with a sensor that can be buried in the soil Power supply cord
Thermometer that can read between 55 and 85 degrees Fahrenheit
Potting soil (sterilized) to fill pan
1/2-inch mesh hardware cloth

COST:
Baking Pan $2.49
Thermostat $ ?
Thermometer $1.19
Power Supply Cord $1.00
Heating Cable $2.00
Potting Soil $.59
Hardware Cloth $.22

TOOLS & SUPPLIES:
Wire cutters
Wire strippers
Screwdriver (slotted)
Tin snip

ASSEMBLY PROCEDURES:

1. Place 1/2 inch of potting soil in pan.
   
   
2. Wire thermostat between power supply cord and heating cable. Thermostat sensing bulb should remain out of pan until all soil is added.
   
   
3. Place heating cable over soil to provide 10 watts per square foot of pan surface. Uniform spacing is important.
   SAFETY CAUTION: Do not cross one cable over another. This creates a hotspot and could result in a short. Never shorten the cable length, because the shortened cable may become hot and burn out.
   
   After cable is in position, cover it with 1/2 inch of soil, then place a 1/2-inch mesh hardware cloth on top of the soil. Then fill with soil.
   
   Place thermostatic sensing bulb in center of pan 1/2 inch underneath the soil. Do not work soil below mesh and disrupt cable since this could result in cable damage.
   
   
4. Refer to horticultural manuals for planting, fertilization, growing and transplanting of seedlings.  Plant seeds and place thermometer in center of soil to depth of hardware cloth.

BASIC ELECTRICAL CONCEPTS:

Electricity with a thermostat can provide controlled heating which can provide faster and more effective seed germination. An electric circuit with an off/on thermostat switch can provide uniform heating within a desired temperature range.