Sheri George’s husband had good intentions. After moving from Texas to Colorado for Christmas, the high altitude wind and unanticipated temperature fluctuations were ruining her outdoor garden. Lee decided to buy her a greenhouse kit. The gesture was perfect. Sheri would soon discover that it wasn’t.
In a small, enclosed space, temperatures can drop from a reasonable morning chill to a scorching afternoon furnace in a matter of hours. In their first greenhouse, most novices learn this the hard way.
She recorded days when the temperature fluctuated between 32 degrees Fahrenheit in the morning and more than 110 degrees in the afternoon. As a result, the plants suffered. Despite outgrowing her old greenhouse, Sheri continues to cultivate greenhouses in her 13-by-20-foot structure in Atlanta that her husband built after she outgrew it. Anyone just starting out should go bigger than you think they need, because you will fill it and a larger air volume prevents temperatures from rising too high.
Recent years have seen the market for mini greenhouse kits expand significantly, ranging from a $43 portable pop-up to a fully equipped aluminum structure that costs well over a thousand dollars. When a novice stands in front of that range, the options seem more like a test than a shopping experience. It may not be possible to find a single kit that works for everyone, but some mistakes cost people money in ways they could easily avoid. A good example is the 6-by-4-foot models that frequently appear at the bottom of search results; they are small, cheap, and insufficient for most applications. At the 6-by-8-foot size, the math usually favors the gardener.
It is more important than you might think to choose the right frame material. In humid climates, experienced greenhouse gardeners almost never experience wood warping. Despite the fact that PVC plastic frames are less expensive and hold up fairly well, UV exposure deteriorates the material over time, and a lightweight plastic structure in a high-wind area could easily collapse. It is widely accepted that aluminum is the most practical option, as it is widely available, reasonably priced, and corrosion-resistant for many years without requiring significant maintenance. One wrinkle remains. Sheri and Lee painted an aluminum kit they purchased unfinished. In the end, they regretted this choice because the paint chipped and needed frequent touch-ups. Powder-coated aluminum requires little maintenance after installation and is slightly more expensive.
Among greenhouse components, glazing-the panels that let light in-generates more controversy than anything else. The glass seems flawless and lets in great light, but a football from next door, a stray garden tool, or a hailstorm can suddenly break it. In particular, twin-wall polycarbonate panels are nearly unbreakable and offer superior insulation. A windy garden benefits from toughened safety glass because the additional weight keeps the frame more grounded. Heat retention is best achieved with triple-wall polycarbonate if money permits. In the winter, clear panels perform better than frosted ones for seedlings that require the most light.
Ventilation is the most common cause of plant death, which is often overlooked by first-time buyers. Heat accumulates faster in a closed greenhouse than it is physically possible. Because they contain a wax compound that expands in response to temperature, automatic roof vents are well worth the extra cost. One afternoon, you forget about the strategy of manually opening panels. It is also important to have fans. A gable-mounted fan and oscillating floor fans keep the air moving and prevent pockets of hot, stagnant air. An alarm that can be connected to a phone eliminates the anxiety of being inside and wondering if something went wrong outside.
A well-stocked garden center’s greenhouse kit section gives the impression that most of the products are marketed as solutions but aren’t. There are numerous accessories that are just as important as the kit itself, such as staging and shelving to lift plants off the ground, shade cloth for maximum summer intensity, and heat mats for seedlings in cold weather. Until they become muddy and harbor pathogens, bare earth floors are practical. The crushed marble, which Sheri ultimately chose, reflects winter light back into the structure, but pea gravel is a workable and reasonably priced alternative.
The floor, the vents, the fans, the shelving, and the temperature monitor are often the hidden costs of a mini greenhouse kit during the first week of ownership. There is nothing particularly exciting about any of those purchases. They distinguish between a structure that cultivates plants from one that gradually destroys them. The kit is only the beginning of the conversation.