Greenhouse Comparisons

The decisions with the longest consequences. Glazing choice trades light transmission against insulation, and there is no option that wins on both.

• Hoop house versus greenhouse A film tunnel gives roughly five times the covered ground per dollar. A rigid greenhouse gives insulation, a door that seals and a structure that lasts. Which one you need depends on whether you are extending a season or changing it.
• Polycarbonate versus glass Glass passes more light and lasts a lifetime. Twin-wall polycarbonate insulates better, survives hail and weighs almost nothing. Which matters depends on your climate and your frame.
• Poly film versus polycarbonate Film is the cheapest covered square foot available and a three to four year consumable. Polycarbonate costs several times as much per square foot and lasts ten to fifteen years while insulating twice as well.
• Twin-wall versus triple-wall polycarbonate Going from 4 mm twin-wall to 8 mm triple-wall raises R-value from 1.54 to 2.10 and drops light from 80 percent to 74. Whether that trade is worth making depends almost entirely on whether the house is heated.
• Aluminum versus wood greenhouse frames Aluminium needs no maintenance and conducts heat straight out of the structure. Timber insulates at the frame, takes a screw anywhere, and needs looking after. Which matters depends on how you use the house.
• Cold frame versus mini greenhouse A cold frame is low, heavy-lidded and holds warmth into a frost. A zip-cover mini greenhouse is tall, cheap and useless in wind. Which one you want depends on whether you are hardening off or overwintering.
• Lean-to versus freestanding A lean-to gets free heat from the house wall and half the light. A freestanding house gets light from every side and loses heat from every side. Aspect decides this more than anything on the spec sheet.
• Row cover versus a cold frame Fabric costs a fraction as much, covers any area and can stay on through the day. A frame protects better and lasts years. Weight of fabric matters more than most people realise.

Running costs and what happens on the coldest night and the hottest afternoon.

• Electric versus propane greenhouse heat Propane is cheaper per BTU and adds water and combustion products to a sealed space. Electric is capped by the circuit, costs more per BTU, and adds nothing to the air. The right answer depends on house size more than on price.
• Evaporative cooling versus shade and venting Ventilation cannot take a greenhouse below outside air temperature. Shade reduces the heat arriving. Evaporative cooling is the only stage that goes below ambient, and only where the air is dry enough to take up water.
• Shade cloth versus whitewash Whitewash is the cheapest way to shade a large glasshouse and comes off on your schedule only in the loosest sense. Shade cloth costs more, gives a specified percentage, and can be removed in ten minutes.
• Bubble insulation versus thermal mass Insulation slows heat leaving and costs light. Thermal mass stores daytime heat and gives it back at night, costing nothing but floor space. They solve different halves of the same problem.
• Oil-filled radiator versus greenhouse fan heater Both are 1500 W and both deliver the same BTU. The difference is air movement, moisture tolerance and how evenly the heat reaches the far end of the house.
• A heater built-in thermostat versus an external controller The dial on the heater measures air the heater just warmed. A separate controller measures where the plants are. That difference costs money every night of the winter.

Passive openers against powered fans. Which one depends on greenhouse volume and whether you have power at the site.

• Vent opener versus exhaust fan A wax vent opener costs a fraction of a fan, uses no power and prevents the specific failure that kills hobby greenhouse crops. A fan moves far more air and needs a circuit. Most houses need both, in that order.
• Shutter fan versus inline duct fan A shuttered wall fan moves the whole volume and seals when it stops. An inline duct fan moves a smaller airflow you can put exactly where you want it. They are not competing for the same job.
• Circulation versus extraction One moves air around inside the house and the other throws it out. Buying only the second is why a well-ventilated greenhouse still gets botrytis.
• Dehumidifier versus venting Venting is free and takes heat with the moisture. A dehumidifier keeps the heat and costs electricity. In a heated winter house the arithmetic is closer than it looks.
• Humidifier versus misting system A humidifier raises humidity in a volume of air. A misting system puts water onto and around specific plants. Propagation needs the second more often than the first.

Lighting for seed starting, and how you get water to the beds.

• LED versus fluorescent for seed starting LED strips deliver more photons per watt, run cooler and last far longer than T5 fluorescent tubes. Fluorescent remains cheap and adequate for a single bench. What matters is delivered PPFD at the canopy, not the fixture type.
• Heat mat versus heated bench A thermostatically controlled mat under a tray is the cheapest way to hold germination temperature. A heated bench does the same across a whole propagation area. Both beat heating the air, by a wide margin.
• Drip irrigation versus hand watering Hand watering lets you inspect the crop daily and adjust to it. Drip delivers the same volume at the same time whether or not anyone is there. The failures each one causes are different, and one of them is much more expensive.
• T5 versus T8 LED strips On modern LED strips the T5 and T8 labels describe tube diameter, not output. What matters is the wattage, the length and how close you can hang it, so compare those and ignore the number in the product name.
• A ready-made light stand versus strips on a shelf A stand with lights fitted removes the wiring and hanging job and costs more per watt. Strips on your own shelving cost less and let you match the light to the crop. Which is right depends on whether you want a project or a working bench.
• PAR meter versus lux meter A lux meter measures light as the human eye sees it and costs a third as much. A PAR meter measures the light plants actually use. The cheap one is useful if you know what it cannot tell you.
• Capillary matting versus self-watering trays Both water from below, which is the single change that prevents most damping-off. Matting suits a whole bench of mixed pots. Wicking trays suit standard cell trays and cost a fraction as much.
• A raised bed versus grow bags A bed holds more soil, buffers water and temperature and lasts years. Bags cost a tenth as much, can be emptied and replaced between crops, and break the disease cycle that catches greenhouse tomato growers.

Raising transplants: what you sow into, what holds it, and what the roots do at the edge of the container.

• Soil blocks versus plug trays Blocks air prune the roots and use no plastic, but they need a specific mix and they dry out fast. Plug trays are quicker, cheaper to fill and forgiving. The right answer depends on how many seedlings you raise and how often you are there to water.
• Peat pellets versus coir pellets Both expand in water and both avoid root disturbance. Peat holds water more predictably and acidifies; coir is the peat-free option, wets more easily once dry and often arrives with nutrient already in it.
• Seed starting mix versus potting mix Seed mix is fine, low in nutrient and free draining because a seed carries its own food. Potting mix is coarser and fed, because a growing plant needs both. Using one for the other is behind a lot of failed sowings.

A closed structure concentrates pests and excludes the insects that would otherwise pollinate the crop.

• Neem oil versus insecticidal soap Soap kills soft-bodied pests on contact and leaves nothing behind. Neem works more slowly and interferes with feeding and moulting. Both need thorough coverage and neither should be sprayed onto a hot, bright, stressed crop.
• Sticky traps versus biological control Traps monitor, and catch some adults as a side effect. Predators control. Under glass biological control works far better than it does outdoors, because the predators cannot simply leave.