Are Mini Plastic Greenhouses Any Good? Garden Tips 2022

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are mini plastic greenhouses any good

Mini plastic greenhouses are often less than 10 square feet in size, though some are 25 square feet or more. Their height varies, so the taller they are, the more plants they will be able to accommodate. Most plastic mini-greenhouses are constructed with metal or plastic pipes and they can accommodate 1-3 horizontal shelves. 

Well-designed, maximum-size mini plastic greenhouses work very well. They are considerably cheaper than traditional glass greenhouses. They provide plants with extra protection and effectively increase the growing season. Of course, they do have their disadvantages, but they also have serious advantages.

How well do plastic greenhouses work?

Technically, a greenhouse is a glass structure that is used to rear and grow plants. But over the decades, manufacturers have come up with low-cost solutions to meet the needs of keen home gardeners. 

The most popular mini plastic greenhouses are made with some sort of metal frame that is covered with flexible plastic. Polycarbonate plastic designs are also available, but more expensive and a lot harder to find.  

While mini plastic greenhouses have limited functions, especially because of their size, they can work really well. For starters, they retain the heat for longer and are considerably more adaptable than traditional glass greenhouses. 

But it depends on the design of what you buy or build. For instance, if you do a quick search on Amazon for commercially available items you will find lots of very small covered shelf units. 

These definitely don’t fit the accepted definition of a greenhouse, regardless of the material used to make it. Even a mini, gazebo-style structure is a bit smaller than most gardeners would probably like. They simply have too little space to work. 

We suggest that anything less than 3 feet x 2 feet in size isn’t worthy of the title greenhouse. But, if you have a tiny deck and want to germinate seeds in a covered shelf unit, then maybe you’ll accept the “greenhouse” description because it suits your needs! 

You can, though, get a mini plastic greenhouse for your backyard that is about 5 x 5 feet and 6½ feet tall. Even though it’s still small, that’s big enough for you to be able to walk into and move around.

Just be sure if you’re buying a ready-made unit online that you know what you’re getting. For instance, what color is the plastic, what weight can the shelves hold, and does it incorporate a breathable window? Be warned that some designs are sold without a frame. 

Advantages of Using Mini Plastic Greenhouses

advantages of mini plastic greenhouses

Mini-plastic greenhouses have lots of advantages. Here are some of them:

Space Savers

Mini-plastic greenhouses are compact and ideal for gardeners with limited space. 

Even though many designs are more like covered tiered shelving than a greenhouse, you’ll find walk-in space-saving designs with an area of 25 square feet or more. Your choice will depend on the space you have available, but that’s smaller than the average garden shed.  

Price

Mini plastic greenhouses are relatively inexpensive, though you will pay more for good quality products. In a random check on Amazon, we found these current prices for unassembled mini greenhouse kits. 

All are walk-in designs that are covered with flexible plastic. Every single polycarbonate design we sourced on Amazon was currently unavailable.

Size is shown as length x width x height. Price excludes delivery:

  • Powder-coated metal frame with polyethylene (PE) cover – 6 shelves – 56 x 29 x 77 inches – $52.99
  • Heavy-duty tube frame with PE cover – 2 windows, 4 shelves – 61 x 28 x 79 inches – $67.99
  • Heavy-duty powder-coated steel pipes with PE cover – 4 wire shelves – 61 x 28 x 79 inches – $56.99 (marked down from $84.99)
  • Tubular iron frame with PE cover – 4 wire shelves – 56 x 29 x 77 inches – $59.99 (marked down from $79.99)
  • Steel frame with polyvinyl chloride (PVC) cover – 56.3 x 56.3 x 76.7 inches – 8 shelves – $89.95

Prices on the Greenhouse Megastore website include glass, polycarbonate, and PE film greenhouse designs from a variety of manufacturers. Here are a few examples for comparison:

  • Steel frame with triple-layer PE cover – 120 x 120 x 96 inches – $399
  • Powder-coated steel with triple-layer PE cover – 160 x 240 x 102 inches – $1,199.00
  • Galvanized steel frame with twin wall polycarbonate panels – 118.1 x 159.86 x 94.5 inches (about 10 x 13 x 8 feet) – $3,091.00
  • Aluminum frame with polycarbonate covering – about 6 x 8 x 7 feet – $1,022.35
  • Glass with aluminum frame – ft 9 ins x 12 ft 6 ins x 8 ft 2 ins – $7,300.00

Usefulness

Mini greenhouses are particularly useful for seed starting and plant cloning. You can use them outdoors, in the garden, on terraces and decks, and if they are really small, indoors as well. 

They are easy to move. So, if you have severely cold winters, you can relocate your mini greenhouse to a sheltered space that is easily accessible. 

If you have a garden allotment, you could move it there too. 

Heat Retention

Plastic greenhouses generally retain heat extremely well. If you live in an area that experiences severe cold in winter, it’s relatively easy to add a layer of horticultural bubble wrap inside to increase the temperature even more. 

Disadvantages of Using Mini Plastic Greenhouses

While mini-greenhouses are small and therefore relatively easy to maintain, their size can be a disadvantage. It’s not just because they can accommodate fewer plants, but they are also typically less stable than other larger structures. 

Size 

Glass and plastic greenhouses both vary substantially in size and both are also available in small sizes. As mentioned above, many so-called mini-greenhouses are simply metal shelves that are sold with a fitted plastic cover. 

You can see from the list with prices above what typical sizes of mini plastic walk-in greenhouses are. 

If you want a larger plastic structure, your best option will be a plastic tunnel. But it doesn’t have the same features as a greenhouse and is better suited to agricultural needs.  

Instability 

In windy areas, instability can be a major problem. Even long, plastic-covered growing tunnels can get whipped up by the wind and damaged, if not destroyed. 

Heat Retention

While heat retention is a huge advantage in winter, it can be a bit of a drawback in the summer months. The potential problem is that plastic greenhouses will attract and trap heat very effectively, but they won’t release the heat fast.

What this means is that in summer, when it gets really hot, this trapped heat can harm your plants. But most walk-in plastic greenhouses have zippers and roll-up doors that you can open when the weather heats up.

The caveat here is that you will lose humidity. 

The best way to overcome this problem is to ensure you have adequate ventilation in the summer. Ideally, you need vents on the roof and the sidewalls, but it’s not that easy with a simple plastic structure. 

Another possible solution is to shade the roof of your mini greenhouse.

Mini Plastic Greenhouses Vs Glass Greenhouses: Difference?

The two obvious differences between glass greenhouses and mini plastic greenhouses are size and the materials used to make them. Both of these translate immediately to cost differences, with mini plastic greenhouses costing a lot less than a glass greenhouse, irrespective of its size. 

Durability & Efficiency

You might expect a glass greenhouse to be more efficient than a plastic mini-greenhouse, but plastic has better heat retention properties. Glass structures are, though, much more durable and you can utilize internal heat sources if needed. 

At the same time, the glass will be likely to break if branches of trees get blown off in a major storm. But then, most plastic materials will tear, even if they don’t get subjected to any form of impact. 

Longevity

There is no argument about the longevity of plastic vs glass greenhouses. Glass will always last longer, unless, of course, someone or something (like a violent storm) breaks the glass. 

Even a high-quality, UV light-resistant plastic mini greenhouse isn’t likely to last more than four years. If it isn’t UV-resistant, it’s probably not going to last more than a couple of years. 

A well-made glass greenhouse will usually last for anything between 30 and 50 years, provided there isn’t any damage during this time. 

Then there’s the in-between solution, polycarbonate. Predictably, their pricing is between glass and flexible plastics like PE and PVC. 

You can usually gauge longevity by the warranty offered on the product. 

Size Differences

While glass greenhouses can be large, mini plastic greenhouses are almost always small. 

Typically, mini plastic greenhouses range in size from about 12-25 square feet. Their width varies from about 4-5 feet.

Glass greenhouses used by commercial growers can be wider than 20 feet. Those commonly used as hobby greenhouses range from 8-10 feet in width. 

In both instances, you will find designs with equal width and length. But others that are half the length. 

Price

Mini-plastic greenhouses are considerably cheaper than glass greenhouses. So, home gardeners and even very small-scale commercial gardeners can easily benefit from a quick return on investment (ROI).

On the other hand, serious home growers and large-scale commercial growers will be better off with a bigger investment that will reward them with a much higher return. So, it’s worth considering a glass greenhouse or perhaps one made from polycarbonate that is priced in between. 

What’s the best plastic-type for your plastic greenhouse?

what's the best plastic type for your greenhouses

The most common plastics used for mini-greenhouses are rigid polycarbonate, and flexible polyethylene (PE), and polyvinyl (PVC). Another type is Polypropylene copolymer (PPC) plastic. 

Polycarbonate

Polycarbonate plastic is considered to be the next best option after glass. Rigid and tough, it is more durable than other plastics.

It is also lightweight and offers UV protection. It is, though, considerably more expensive than other types of plastic. However, it will last for at least 10 years if properly maintained. 

Polyvinyl Chloride

Manufactured in both rigid and flexible forms, PVC is hardy and the flexible type lasts longer than PE. But it stands to reason that it is also more expensive than PE

PVC greenhouses will usually last about 5 years if properly maintained and cleaned regularly. 

Polypropylene Copolymer

The copolymer material used for mini plastic greenhouses lasts longer than PE but not as long as PVC. Some reviews say that it tends to become brittle after about 3 years and can break. 

Polyethylene 

PE is the most widely produced plastic of these four types and the cheapest. 

It is available in commercial and utility grades. You can expect the utility grade, which is normally used for greenhouse coverings, to last for a couple of years.  

What can you grow in a mini plastic greenhouse?

You can germinate just about any seeds and let them grow into sturdy seedlings ready to plant out in your garden. But, mini plastic greenhouses are also ideal for growing bush-like vegetables and vines including tomatoes, chilies, sweet bell peppers, cucumbers, and aubergines. 

Most herbs do well in mini-greenhouses too, providing you with fresh seasoning for cooking all year round. 

If you’ve germinated seeds indoors, a mini greenhouse is an ideal place to let the seedlings grow a little bigger. This will also start to acclimatize the plants to outdoor conditions. 

Of course, you aren’t restricted to growing only edible plants. You can keep your favorite perennials that aren’t cool-hardy alive in a mini greenhouse during the winter months.

another alternative is to use it for starting plant growth of annual flowers so that they are ready for planting out in early spring. You can also harden young plants while protecting them from the elements. 

Will a mini plastic greenhouse protect from frost?

Any type of greenhouse will protect your plants from frost – to a certain extent. The problem is that whatever the material unless the interior is heated when temperatures plummet outside, they’re going to plummet inside as well. 

But unless a glass greenhouse is double-glazed, it’s going to provide less protection from the cold than a plastic greenhouse will. 

Generally, unheated greenhouses are about 5 degrees warmer inside than outside. So, your plants will be relatively safe until the outside temperature drops below zero. 

Conclusion

There’s a remarkably big choice when it comes to mini plastic greenhouses. While some are better than others in terms of design and quality, they can certainly be very useful.

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