Apr. 29, 2024
Agriculture
A Beginner’s Guide to Greenhouses
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There comes a time in every plant parent’s life when we start to get curious and excited about having a dedicated space for all of our plants. If you’re an outdoor gardener, the promise of a greenhouse for seed starts and overwintering plants is even more exciting!
If you feel like you’re ready to take the leap of installing a greenhouse – whether it’s a small kit, or a large structure in your backyard – consider this blog a beginner’s guide to building the greenhouse of your dreams!
This blog is inspired by Episode 151 of Bloom and Grow Radio Podcast, where host Maria Failla interviewed Patrick Grubbs, founder of Greenhouse Info.
Do Greenhouses Need Permits?
Before you even begin shopping for greenhouses, you need to consider licensing and permitting. In the US, we have two authorities you should keep in mind when you’re building a greenhouse: zoning regulations and building codes. Almost always, you can simply contact your local government office and they’ll be able to tell you all of the required permits for an accessory building with a permanent foundation.
The one exception? If you’re getting a small greenhouse (or a cold frame) where you don’t need to set up a foundation, those generally aren’t regulated since they aren’t really considered permanent structures. Usually, these are cheaper greenhouse kits that cost about $500 or less.
What’s the Best Greenhouse Construction Material?
Here are the pros and cons to each type of greenhouse material to help you choose the best option for your space.
Glass is a classic greenhouse material.
Pros
: it lasts forever and is easy to maintain. It’s a great long-term option for permanent greenhouses.
Cons
: it’s expensive, fragile, and not a great insulator in general. Insulation is really important for greenhouses, especially if you’re in a Northern climate.
Polycarbonate is one of the most common greenhouse materials.
Pros:
it’s strong, durable, and much lighter than glass.
Cons:
it starts to yellow and degrade after about 10 years, reducing the amount of light to your plant. Opt for the UV resistant choice to help it last longer.
Acrylic is another common greenhouse material (brand names like plexiglass).
Pros:
strong and durable
Cons:
fairly expensive and heavy, contracts with temperature fluctuations so you may need a special mounting solution to attach it.
Polyethylene is another plastic greenhouse material.
Pros:
can buy rolls of plastic to replace material
Cons:
flimsy plastic, likely only used as a temporary material as it’s really only good for one season
Should I use a Greenhouse Kit or DIY My Own Greenhouse?
For a beginner greenhouse hobbyist, a kit is a great option. It’s more affordable, has instructions, and great to start with. A smaller 6’ x 8’ kit that doesn’t need a foundation is a good option and will take a few hours to put together with a group of helpers. Once you get into more of the reclaimed windows and doors for a do-it-yourself greenhouse, carpentry skills are much more of a necessity.
If you want a permanent structure with a foundation and electricity, it might be time to look into other options outside of kits. This kind of project could require a backhoe, 6’ holes, and electrical wiring to get it up and running.
How Much Should I Pay for a Beginner Greenhouse?
A standard 6’ by 8’ greenhouse kit is one of the cheapest starter greenhouses you can get. These kits will probably run you about $500 to $600 for a new kit. Pro tip: check Facebook Marketplace and Craigslist for used greenhouses–you’ll often find some great options for a fraction of the cost.
When you consider the extra components you need to buy, like fans and heaters, it’ll probably end up costing you around a thousand dollars for a very entry-level greenhouse that will satisfy.
What Direction Should My Greenhouse Face?
The point of a greenhouse is to capture the heat from the sunlight and maximize the exposure your plants get. The best way to do that in the Northern hemisphere is to align the roof of your greenhouse going East to West. That will ensure you get the maximum amount of sun in both Winter and Summer. Keep in mind that this is the reverse if you’re in the Southern hemisphere.
What Kind of Floor Should My Greenhouse Have?
The primary consideration for your greenhouse flooring is drainage. If you have a big greenhouse, you might have a foundation underneath like a concrete slab. And in this case, you need to be sure that any water you pour in your greenhouse can get out.
If you don’t have a foundation, you still have the same consideration regarding drainage, it’s just much easier to handle. It can be as simple as concrete pavers with gravel in between. That provides a flat surface, it’s easy to clean and walk on, and it’s stable. Since there’s space in between the pavers, there’s room for water to drain into the ground.
Greenhouse Ventilation Requirements
Greenhouses are super effective at their jobs. They can raise the temperature anywhere from five to 30 degrees Fahrenheit greater than the ambient temperature. You could very easily cook your plants if you don’t have proper ventilation.
The first thing you need to do for all of your greenhouse air conditioning needs is to calculate the total volume of your greenhouse. Multiply the length times the width times 1.5 of the height, which accounts for the volume that isn’t really there at the top. This number will tell you the cubic feet of air in your greenhouse.
You’re going to reference this number whenever you’re looking at ventilation or heating options. You want to try to cycle all of the air in your greenhouse in one minute. If you have a 10’ by 10’ by 10’ greenhouse, that equals 1,000 cubic feet of air. You then need to find an exhaust fan that is rated to push 1,000 cubic feet of air per minute.
Greenhouse Fans
There are a couple types of fans for greenhouses. First is a shop fan or a desk fan, which works for pushing air around, but it’s not the most effective way to cool a greenhouse.
And second is an exhaust fan that’s set into the walls of your greenhouse and moves air from inside to outside and vice versa. Usually these fans come in pairs so you can put one on each side of the greenhouse to circulate air efficiently.
Further reading:If you are looking for more details, kindly visit glass greenhouses for agriculture factory.
Greenhouse Vents
There are many different kinds of greenhouse vents, but the best options are solar vents. They have wax inside of them that expands and contracts when it gets warm, which automatically opens and closes the vents with no electricity. Most greenhouse kits you buy probably won’t have any ventilation built in, so make sure to factor that into the cost of building a greenhouse.
Ventilation is a necessity for a greenhouse in order to control the humidity, temperature, and air flow. Plan to incorporate fans and vents for proper greenhouse ventilation.
Managing Humidity and Mold in Your Greenhouse
Ventilation is your number one defense against humidity. A trick to dealing with root rot or mold is to have airflow underneath your pots.
Many greenhouses have plant benches and the bottom of the bench is actually a grate so air and water can freely flow through. This is important because it means the air accesses the plant roots, which is where plants take in most of their oxygen. Having that additional airflow dries out the potting media faster, which will help prevent mold and rot.
What’s the Ideal Greenhouse Temperature and Humidity?
A good greenhouse temperature is around 80 to 85 degrees Fahrenheit, but it all depends on what you’re growing. Opt for low humidity, especially in Summer, so temperatures are more bearable.
To really control the temperature in your greenhouse, try a remote thermometer. It makes monitoring the temperature much easier, especially when dealing with snow and freezing outdoor temperatures. You can also plug all of your appliances into a smart plug bar. The bar allows you to connect to Bluetooth using an app, which helps you control temperature, light, and humidity from your phone.
3 Beginner Greenhouse Tips from Patrick
Tip 1: A greenhouse isn’t necessarily the next step for improving your gardening skills. It’s a whole different category. Unfortunately growing in a greenhouse alone won’t make your plants healthier and happier: there’s a learning curve. Make sure you dial in the right parameters to optimize growth in your greenhouse to get those happy plants.
Tip 2: You will deal with pests in greenhouses, but you have options. Greenhouses can actually give you enough space for a dedicated quarantine section of insect-ridden plants. You can use a corner shelf with all of your remedy supplies, far away from other plants. Put a sticky note with the date you placed it on the shelf, then transition it to the rest of your plants after about a month.
You can also implement predatory insects in your greenhouse. Some great examples are ladybugs, praying mantises, lacewings, and parasitic wasps. Just make sure you’re not purchasing the invasive ladybug.
Tip 3: If you’re not in a place in your life where you expect to be there for a while, then a greenhouse probably isn’t the best option. It’s a big investment in terms of money, time, and space. Many of them are at least a 10 year commitment unless you have a way to transport it. You still have options, like a cold frame or something a bit smaller like a grow tent.
To learn more about greenhouses, check out Patrick’s website Greenhouse Info.
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About Bloom & Grow Radio Podcast
Bloom & Grow Radio Podcast helps people care for plants successfully and cultivate more joy in their lives. Host Maria Failla, a former plant killer turned happy plant lady, interviews experts on various aspects of plant care, and encourages listeners to not only care for plants, but learn to care for themselves along the way.
About Our Interviewee
Patrick Grubbs has a B.S. in Biology, where he fell in love with plants through his first botany class. He’s published aquatic ecology research and authored several books related to succulents and gardening pests.
Patrick has spent a great deal of his career split between science communication and hands-on permaculture and ecology projects. His passion is teaching other people to enjoy plants and animals the same way he does.
Follow Patrick:
Website
Where to Buy
4 Questions to Ask Yourself | Selecting
a Site for Your Greenhouse
Greenhouse Coverings | Greenhouse
Frames (structures)
You will want your greenhouse to meet both your gardening needs and your pocketbook. This guide can help you decide what type of greenhouse best fits these requirements, whether it is one from us or a different greenhouse.
1. What size greenhouse?
Greenhouse size is usually dictated by factors like available space and construction
costs versus need or desire. When choosing a size, consider if the greenhouse
will be used year-round, seasonally, or mainly as a sunspace. If you want a greenhouse
to house an extensive collection of houseplants, then it is best to plan on building
or purchasing a structure that is larger than your current space requirements.
Most hobby greenhouse owners find they need a larger greenhouse than they originally
thought. Upgrading later on may be more costly than ordering a larger unit
from the beginning. Another important size consideration often neglected
is height. You want to make sure your greenhouse has adequate head room. You need
to consider both peak and eave (sidewall) height. Taller houses are also easier
to heat and ventilate because the air has a greater buffer area.
2. What will the greenhouse be used for?
I want to get a head start in early spring and/or a few
extra growing weeks in late fall.
This is an easy task for a greenhouse. How much extra time the greenhouse will
provide will vary based on your local climate and if you choose to equip the greenhouse
with automatic ventilation and heating. Any of the greenhouses we offer can be
used for season extension since heating and cooling requirements are very low
for this purpose.
I am interested in overwintering plants that are not
hardy in my area.
Overwintering, maintaining the minimum temperature needed for plants to survive,
requires heating the greenhouse even if it is for a short period of time. Greenhouses
suitable for overwintering can also be used for season extending. Inexpensive
greenhouses like the FlowerHouse models
are fine in milder climates that you don't expect needing to heat the greenhouse
more than about 30° F
above the outside temperature for any extended length of time.
If you are in a colder climate with temperatures that sometimes drop to 0°
F or below, a greenhouse with an insulated covering is recommended. These
greenhouses are not only retain heat better, but they also generally offer a tighter
seal than other greenhouses making them easier to heat. The Cross
Country, Grow More, Solar
Harvest, and Sunshine models would be better
suited for this purpose.
I want to grow plants in a greenhouse during the winter.
This is different from overwintering plants because plants generally need higher
temperatures to grow and thrive versus just staying alive. In this case, an insulated
greenhouse will be worth the extra investment because of the lower heating cost.
The Cross Country, Grow More,
Solar Harvest, and Sunshine
models are better greenhouses for growing in the winter.
I want a greenhouse to grow plants year round.
A tightly sealed and insulated greenhouse with high light transmission is desirable
for year-round vegetables and flowers (especially in northern climates). Remember,
greenhouses are designed to store heat from the sun and create a warmer environment
inside of them, so use in the summer in most areas would be limited at best. A
greenhouse with an evaporative cooling system is recommended to keep temperatures
at a minimum when it is hot outdoors.
3. How elaborate do you want the greenhouse to be?
If you are just starting seedlings or wintering over a few plants and are looking
for the least expensive option to do so, you should consider the FlowerHouse.
If you want your greenhouse to be a focal point as well as functional, the Sunshine
and Cross Country greenhouses are among our most attractive
structures. The Cape Cod and Cottage
series of the Cross Country are available with a combination of glass and polycarbonate
providing both beauty and function.
4. Is a building permit required?
Check local ordinances for required setbacks from property lines, design requirements,
and other requirements. Call your local building department. Some hobby
greenhouses may not need a permit, but it is a good idea to check anyway.
Most important is the covering. It will determine the amount
and type of light reaching your plants, the overall appearance of your greenhouse,
its safety, ease of maintenance, and longevity.
- Glass -
The traditional greenhouse covering, preferred for its permanence and beauty.
Glass is one of the least efficient materials for retaining heat, because it transmits
heat and cold quickly and has very little insulating value (that's why it is used
in cooking utensils and thermometers). Greenhouse glass should be double or triple
strength to increase heating efficiency and decrease breakage which can be dangerous
when installing as well as a problem in the completed greenhouse.
Glass is much heavier than other coverings, requiring more substantial framing. Other disadvantages include: it doesn't diffuse light, so there's a risk of burning plants; glass breaks more easily than the plastic coverings (important if you have hailstorms, trees nearby, kids that play baseball, etc.); and finally, slight deviations from horizontal and vertical frame alignment or settling of the foundation can crack it. Most glass greenhouses use either engineered aluminum, steel, or laminated wood frames with full foundations. Never install glass on breezy days. Because of the need for many smaller, overlapping, glass segments in these greenhouses, site selection should take wind into consideration. Air (heat) leakage is greater in glass greenhouses because of the many panes needed.
If you are unsure about your building talents, you might do well to avoid glass as the frame must be absolutely square and rigid. If you must have glass, consider hiring a contractor for your installation.
- Plastics - These coverings include fiberglass, polycarbonate, acrylic sheets, and polyethylene film. All plastics resist hailstone damage and are shatterproof, a distinct advantage over glass. Rigid plastics are stiff, but not brittle. They can be flexed to fit over a curved surface and are available in large sheets. This reduces the number of potential air leaks by reducing the number of joints in the covering.
Fiberglass
The first of the practical replacements for glass, fiberglass usually comes in
rolls or corrugated sheets and is translucent rather than transparent. You
can't see through it but light transmission is roughly equal to glass. Fiberglass
diffuses light that passes through it creating a virtually shadowless greenhouse. Fiberglass
retains heat more efficiently than glass (but not as well as insulated plastics
like multiwall polycarbonate or two layers of inflated polyethylene film) while
transmitting less heat into the greenhouse, a benefit in both winter and summer.
Its corrugated form allows overlapping sides to seal well but its undulating ends can make for difficult joints. Aesthetically, the corrugations tend to detract from the structure and grime can collect in valleys. Greenhouse fiberglass is UV protected by a gel coat that will eventually be baked off by the sun lasting only about 6 years before turning yellow. When this happens, dirt accumulates among the glass fibers and becomes very unsightly.
Polycarbonate
One of the newest covering options, UV treated polycarbonate provides much of
the clarity of glass and is stronger and more resistant to impact than other coverings.
It is also more resistant to fire than other plastics. View
picture of polycarbonate
Polycarbonate is available in several different thicknesses and normally comes in single, double, and triple walled sheets with many structural walls separating its two flat sides. Single wall polycarbonate is the least expensive and is generally used for its attractive appearance, but it lacks the strength, heat retention, and light diffusing properties of double and triple wall polycarbonate. The multiwall structure gives it greater strength and superior insulating values with the air space built into the product. Multiwall polycarbonate also provides your greenhouse with an even diffused light that minimizes shadow and is optimal for growing plants. Another advantage of polycarbonate is its +15 year lifespan in most areas. Double walled polycarbonate is used to cover the Solar Harvest and Sunshine greenhouses. Triple and 5 wall polycarbonate panels like available with the Grow More and Cross Country greenhouses are more expensive than twin wall options, but they will pay for themselves in reduced heating costs in cold climates that require frequent heating.
Polyethylene Film
A favorite of commercial growers because of its simplicity of maintenance. Use
it for 3 to 5 years (life depends on poly thickness and UV treatment used) then
recover with new poly. Used in single thickness, polyethylene film is good
for simple cold frames and greenhouses used for starting seeds and other seasonal
needs. When two layers are used, and the space between is inflated by a fan creating
insulated air space, the polyethylene film retains heat more efficiently than
glass houses, saving roughly 40% in heating costs.
Drawbacks to polyethylene film include a relatively short lifespan vs. other coverings, possibilities of rips and tears, and a translucent appearance much like fiberglass. Polyethylene's low cost, ease of replacement, high light transmission, and good heat retention have made it a favorite of nurserymen and commercial growers.
There are differences in polyethylene film. Cheap, thin films sold at many
hardware stores and home centers are unsuitable for greenhouse use. Those films
are designed as vapor barriers in home construction and other "interior" uses.
Greenhouse polyethylene films are specially coated for protection from UV (ultraviolet)
rays which shorten the lifespan of unprotected film. There's a minimal cost difference
and a considerable difference in performance on your greenhouse. The FlowerHouse
greenhouses use a new woven polyethylene which is more durable.
Galvanized Steel
Most commercial greenhouses have galvanized steel frames because they are long-lasting,
low cost, and require less framework (thus less shadowing) than any other framing
material thanks to steel's natural strength. Steel's greatest value in greenhouse
construction is its strength. You want as much light to enter your greenhouse
as possible and steel frames can be thinner than others, creating less shadow.
Its other big advantage is its low cost. Steel greenhouses are normally covered
with polyethylene film because most frames are not designed to accommodate rigid
panels without additional hardware. Be sure that any steel tube greenhouse you
purchase is made with heavy-duty galvanized or stainless tubing which is made
for outdoor construction purposes to protect it from a greenhouse's normal humid
and corrosive (fertilizer salts) atmosphere.
Galvanized metals will eventually wear off their protective finish and rust from
high humidity levels present in a greenhouse. Steel is much heavier than
aluminum and generally requires additional hardware to mount a rigid covering
to it.
Aluminum
Aluminum is used primarily in conjunction with glass or polycarbonate in architectural
sunspaces and hobby greenhouses. It can be anodized in a variety of colors and
has low maintenance requirements. Because of its higher initial cost, aluminum
is most often used with glass and rigid plastic coverings in structures like the
Solar Harvest, Grow
More, and Cross Country greenhouses. Aluminum
is the longest lasting of all of the framing materials mentioned because it will
never rust, rot, or break down from UV rays.
Aluminum does not have the strength of steel so frame members either must be larger or more numerous. Look for engineered shapes in aluminum that are designed to increase frame strength, because you want as little frame shadowing as possible while not sacrificing the integrity of your greenhouse's frame.
Wood
Wood is most commonly used either for sunrooms or in homemade greenhouses.
They are popular because of their attractive look, the ease in which accessories
can be added to them, and the low amount of heat loss they produce compared to
similar size metal frames. Wood frame structures are most often covered with a
rigid plastic or glass. Though very attractive in sunspaces, wood has a limited
lifetime in a greenhouse's damp atmosphere before it starts to deteriorate. Redwood
(used in the Sunshine greenhouse frames) or cedar
is recommended because of their natural resistance to the elements and insects.
Applying a chemical sealant or stain to the wood periodically can also greatly
increase the life of the material.
Wood frames are generally larger and heavier than equivalent metal frames which increases the amount of shadow in the greenhouse. Wood hobby houses are generally small scale with a limited ability to expand once construction is complete.
Plastic
Over the last 10 to 15 years plastic hobby greenhouses have become increasingly
popular. The main advantages of these greenhouses is their low cost, portability,
and ease of installation. Plastic is generally used to construct smaller structures
because it is not as rigid as metal or wood, but the introduction of options like
metal wire supports compensates for what plastic lacks in strength. Plastic
frames have become increasingly popular because of the low amount of heat loss
they produce compared to similar size metal frames. This is because plastic is
a poor heat conductor like wood.
The main drawback to a plastic frame is that ultraviolet rays from the sun will
eventually cause the plastic to deteriorate even if it is a UV protected material.
UV protected PVC materials generally have a 20 year or better life. Plastic frames
are also normally larger than equivalent metal frames which increases the amount
of shadow in the greenhouse.
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