TerraPoniK the affordable premium DIY greenhouse
Serious gardeners in short-growing-season areas have limited choices when it comes to greenhouses designed for their needs. The two dominate options are Growing Spaces Domes and Ceres Greenhouse Solutions DIY plans. Now there is a third: the TerraPoniK greenhouse DIY plans. Lets compare these and discover their strengths and weaknesses.
Size: One of the first decisions a greenhouse buyer has to make is the size needed. If the gardener does not own acreage, but lives on a typical 1/4-acre suburban lot, a large foot-print greenhouse will not fit within the available space once required property set-backs are included. In these instances, only the smallest 15-ft or 18-ft dome can be considered. Ceres GS's smaller 10' x 12' and 12' x 16' are possibilities; but TerraPoniK's compact 8.4' x 16.4' size will most easily fit within tight land area constraints.
Snow: In a short-growing-season area, snow is a common occurrence within the desired growing window. The Growing Spaces dome sheds snow well, the Ceres GS does not. The Ceres DIY greenhouse uses a very flat 2:12 pitched roof (< 10-degree). Any snow landing on such a flat-roof will not slide off and immediately block the sun from your plants. To clear the snow will take a ladder and snow-rake (not fun in cold weather). The TerraPoniK greenhouse has a 12:12 pitch (45-degree) and sheds snow easily.
Ventilation: On sunny days, greenhouses get hot and the smaller the greenhouse the quicker the heat builds.
The smaller Growing Spaces domes come with passive thermal-wax opening vents and one active fan, but company literature admits that more are needed to actually keep dome temperatures below 100F. Once these are added, costs increase and thermal performance is hurt in the winter due to increased air infiltration. The open water tank in the dome helps some, but this help comes with the cost of increased humidity.
The Ceres system is not much better. It relies on its GAHT system to remove interior greenhouse heat and store it in the soil below to keep greenhouse interior temperatures down. Unfortunately, the greenhouse design with the near flat 2:12 pitch presents a maximum solar aperture that completely over-powers the GAHT system's ability to keep up. Combine that with the relatively small ventilation fan and damper used and it is a recipe for scorching +100F interior temperatures. The greenhouse does have many gliding-windows around the walls, but these require manual opening which tethers the gardener to the greenhouse becoming the "temperature conductor".
The TerraPoniK greenhouse is different, glazing is oriented at a 45-degree angle which lowers the solar aperture size by 30% in peak summer sun. Next, the integrated air super-heater captures solar energy before it even enters the interior of the greenhouse to lower the solar heating rate. Finally, the ventilation fan and inlet damper is sized large enough to cap the greenhouse interior temperature at less than 10F degrees higher than the outdoor temperature. In the TerraPoniK greenhouse it is not necessary to manually open any windows to control temperature allowing the gardener the freedom of multi-day trips away.
Overnight Thermal Performance: All of these greenhouse rely on the sun for solar energy to be stored and later released to lessen overnight cooling. In cloudy and cold climates, none of these greenhouses will give good thermal performance and will require back-up heat.
Growing Spaces passive-heater is their large open water tank. It is fully passive (no fans) but has its short comings. First the rate of heat release is not controllable. It is not possible to delay the heat release to when it might be better used later in the night. Second, the heat release comes with a large release of humidity, which then condenses on your plants to enhance the risk of mold, fungus and other plant diseases. This humidity also triggers a water distillation loop where the water tank evaporates the water and all the cold dome glazing condenses the water. This process degraded the insulating value of the glazing by about 20% increasing heat loss and upping the heat load needed to keep the greenhouse temperature warmed to the desired level. Growing Spaces website states "In a smaller 15-foot Dome, the pond can store enough energy to keep things warm for two to four hours during a cold night" - then its crank up the electric heaters.
The Ceres greenhouse relies on their proprietary GAHT system (though the design is well known and often copied). The piping layout used is sub-optimal from a pressure-drop standpoint, but is done that way for convenience. The standard layout is the air-inlet in the N-W corner near the ceiling and the air-discharge lower and in the SE corner. Near both the East and West walls (buried parallel to the wall) is the flow distribution manifold and flow-consolidation manifold. Each manifold has many 90-degree branch lines using 4" corrugated perforated plastic drain pipes that are in parallel pipe runs between the two manifolds. To make the branch connections at each manifold, the corrugated pipes are simply "stabbed" through the manifold trunk-line. This type of branch connections is about the worst choice to use if low-pressure-drop is the goal. This restrictive piping then limits the air flow volume that can be easily blown through the pipes, thereby capping the rate of heat capture in the soil.
The next limit is the relatively low peak ceiling height in the Ceres residential greenhouses. This fact will not allow any meaningful temperature stratification to occur and the GAHT inlet temperature will be limited to no higher than 95F (unless you chose to seriously stress your plants).
The final limit is imposed by not insulating below the soil mass being actively heated. Deep soil temperatures in the colder months are never warmer than about 50F. Hence when the overlaying soil is heated up above this lower soil temperature, it leaks heat energy downward and much will be lost unable to later be used to warm the greenhouse above. It is not uncommon for less than 50% of the heat stored during the day to ultimately be delivered to warm the greenhouse.
The Ceres greenhouse uses 16mm triple-wall polycarbonate panels (R-2.5 and solar transmission of 75%). The balance of the greenhouse is well insulated and the likely overall heat-loss-rate for the smallest 10' x 12' greenhouse is estimated at 100 Btu/hr-F. However, the low output from the GAHT system will greatly limit its ability to keep the greenhouse interior much above freezing during cold nights.
The TerraPoniK greenhouse uses a powerful DCB (diurnal-climate-battery) that overcomes the short-comings of the Ceres GAHT design. It has a piping network with less than half the pressure-drop of the Ceres GAHT. This is combined with an integrated air super-heater that warms the injected air temperature to over 125F. The combination of low pressure-drop piping and high inlet air temperature, yield heat injection rates twice that of the typical GAHT system.
The TerraPoniK greenhouse's DCB uses a shallow (2-ft deep) soil mass with surrounding insulation that allows the soil mass to heat up independently from the cold soil below. This reduces the heat-leak to the colder deeper soil that a standard GAHT system suffers from. The result: substantial solar energy is stored in the soil during sunny days and powerfully delivered heating to the TerraPoniK greenhouse interior at night. It is common for the bulk soil temperature in the thermal-battery of reach or exceed 70F . This allows exit air temperatures above 60F.
The TerraPoniK greenhouse glazing is dual layer 8mm twin-wall polycarbonate panels with a 3.5" to 5" air gap yielding R-4.3 insulation value while transmitting 65% of sunlight. This combined with a windowless R-15 insulated North wall, with similar insulation in various other wall surfaces, yields an overall heat-loss-rate value of 102 Btu/hr-F and this value includes a 1-ACH (air-change-per-hour) leakage factor as well. The exceptionally low heat loss matched with the strong DCB output, yields interior greenhouse temperatures well above freezing all night without supplemental heat. During prolong cloudy stretches, the 1500W of electric back-up heat is all that is need to maintain comfortable 50F overnight greenhouse temperatures (down to 0-F night lows)
Irrigation: Watering of plants is a frequent job that benefits with some automation. The premium greenhouses discussed in this article offer:
Growing Spaces offers a "mini-jet-sprayer" watering system for the two small dome sizes (15-ft and 18-ft). This choice is questionable. Geodesic dome greenhouses with open water tank (ponds) are plagued with high-humidity problems. By using spraying nozzles instead of drip-line irrigation only serves to worsen humid conditions within the dome.
Ceres DIY plans do not include any irrigation information. It is left the the buyer to design it themselves or pay Ceres to assist you in the design.
TerriPoniK greenhouse DIY package includes a complete automated drip-irrigation system. Its design is a Trunk-and-Fingers layout that has the main 1/2" water-delivery trunk-line with 44 individual short branch-lines (fingers) in 8" spaced parallel lines. This layout ensures rapid pressure equalization and equal emitter water delivery across the entire growing area.
The watering "fingers" help define the 16"x 16" enlarged (square-foot-gardening) planting squares that fill all the 32" wide planting raised-beds. The water source is a black plastic barrel with pump and timer to deliver the precise volume of water requested. The water in the barrel will be solar heated adding additional thermal mass to the greenhouse. The barrel water can also have liquid fertilizer added for watering and feeding the plants. The water volume is sufficient for 3-to-5 days of unattended watering.
Value: Premium greenhouses tend to be expensive.
Growing Spaces' smallest 15-ft dome kit is $11,950 and that does not include any foundation expenses or the various "consumer supplied" materials. It also does not include the cost of any of the raised-planter-beds. Growing Spaces most popular size (the 26-ft dome) has a basic kit price of $26,850, but they say the typical finished cost is close to $40,000 or 1.5 times the kit price. This ratio suggest a fully completed 15-ft dome may cost upwards of $18,000. One final fact is with the large water tank and circular shape, the 15-ft dome only offers about 65-ft2 of actual plant growing area.
Ceres Residential DIY greenhouse plans cost $950 without the GAHT system design and $1450 with them. The smallest 10' x 12' greenhouse uses four dual-pane gliding residential home windows which add considerable expense. A fully finished DIY build (free labor) with the GAHT, I would estimate at $10,000-$14,000 (higher price if a poured concrete foundation used. This price does not include the $1450 for the DIY plans or irrigation system.
TerraPoniK greenhouse has a full BOM - (bill of materials as of June 2026) of $7400 less tax. With some excavation costs, taxes and the $249 TerraPoniK plan set, the budget is just $9000-$10,000. And remember, this greenhouse includes all the ancillary systems that make it a 3-5 day autonomous growing system. It has a 138-ft2 footprint with 80-ft2 of highly productive growing beds.
TerrraPoniK "Engineered for Growth"