How to Run Electricity to a Greenhouse Safely

Electricity is the greenhouse utility that gets the least planning attention and causes the most headaches when it is inadequate. Grow lights, heaters, exhaust fans, circulation fans, irrigation pumps, and controllers all need power — and in a structure surrounded by water, soil, and humidity, electrical safety requires deliberate planning. This guide covers the electrical needs of a hobby greenhouse, how to supply power safely, and the common mistakes that create fire and shock hazards.

Estimating Your Electrical Load

Add up the wattage of every device you plan to run simultaneously. A typical hobby greenhouse electrical inventory includes: supplemental LED lighting (200 to 600 watts per fixture, 1 to 4 fixtures), electric heater (500 to 1,500 watts), exhaust fan (50 to 200 watts), HAF circulation fans (20 to 50 watts each, 2 to 4 fans), irrigation pump (50 to 200 watts), heat mats (17 to 75 watts each), and controllers/sensors (10 to 50 watts total). A moderately equipped greenhouse may draw 1,500 to 3,000 watts during peak winter operation when lights, heater, and fans all run simultaneously.

A standard 20-amp, 120-volt household circuit provides 2,400 watts maximum (80 percent of the theoretical 2,400 watts for continuous loads). Many greenhouse setups require a dedicated 20-amp circuit at minimum, and larger or heavily equipped greenhouses may need a 30-amp or 240-volt circuit. Running the greenhouse on an extension cord from the house is a fire hazard and a code violation — do not do this.

Getting Power to the Greenhouse

The safest and most code-compliant approach is a buried underground feeder (UF) cable from the main electrical panel to a subpanel in the greenhouse. Use UF-rated cable buried at least 18 inches deep in a trench (or 12 inches deep in conduit). Install a weatherproof subpanel with GFCI-protected breakers in the greenhouse, providing multiple circuits for lighting, heating, and general-purpose outlets.

Hire a licensed electrician for the subpanel installation and connection to the main panel. This is not a DIY project for most homeowners — the main panel connection involves working with live power, and permit and inspection requirements apply in most jurisdictions. The electrician visit is typically the single most expensive infrastructure cost for a new greenhouse ($500 to $1,500 depending on distance from the house and panel capacity), but it provides safe, code-compliant power for the life of the structure.

GFCI Protection

Every outlet in the greenhouse must be GFCI-protected (Ground Fault Circuit Interrupter). GFCI devices detect ground faults — current leaking through water, soil, or a person's body — and cut power in milliseconds, preventing electrocution. Greenhouses are wet environments by definition; GFCI protection is not optional. Install GFCI breakers in the subpanel or use GFCI-protected outlets at each location.

Test GFCI devices monthly by pressing the test button. If the device does not trip, replace it immediately. GFCI devices have a finite lifespan (10 to 15 years) and can fail without warning. A non-functional GFCI provides no shock protection.

Solar Power for Greenhouses

A small solar panel system can power low-draw greenhouse devices: circulation fans, vent openers, irrigation pumps, and sensor/controller electronics. A 100 to 200 watt solar panel paired with a 12-volt battery and charge controller provides enough power for 2 to 3 small fans and a pump running intermittently throughout the day. This is practical for greenhouses too far from the house for an economical underground cable run.

Solar is not practical for high-draw devices like grow lights and electric heaters. A 600-watt LED fixture running 12 hours per day requires 7.2 kWh — you would need 1,500 to 2,000 watts of solar panels and significant battery storage to power it, which costs far more than simply running a cable from the house. Use solar for low-power automation and grid power for high-draw lighting and heating.

Organizing and Protecting Electrical Connections

Greenhouses are hostile environments for electrical connections. High humidity corrodes terminals, water splashes during watering can reach outlets, and temperature swings cause condensation inside junction boxes. Use weatherproof outlet covers (in-use covers that protect plugs while they are connected, not just when the outlet is empty) on every outlet. Wrap all wire connections in waterproof wire nuts or heat-shrink tubing rather than standard electrical tape, which loosens in humid conditions.

Label every circuit at the subpanel: lighting, heating, fans, irrigation, and propagation. This documentation prevents confusion during troubleshooting and ensures you can isolate individual systems without cutting power to the entire greenhouse. A laminated wiring diagram posted next to the subpanel is the professional standard — it takes 15 minutes to create and saves hours of frustration when something trips a breaker at 6 AM in January.

Install a surge protector on the main feeder line to the greenhouse subpanel. Power surges from lightning strikes and utility switching damage sensitive electronics — controllers, timers, thermostats, and LED driver circuits are all vulnerable. A whole-panel surge protector costs $50 to $100 and prevents hundreds of dollars in equipment damage.