How a Greenhouse Works - Greenhouse Gardening at it's Best!

It’s not surprising that my love affair with greenhouses has continued into my adult life!  Owning a greenhouse has been a way of providing my own children with quality, fresh and mostly organic fruits and vegetables.  It is important to know that there is a little bit of knowledge required to cultivating plants in a greenhouse environment; it is a little bit more involved that just putting up a protective structure in your garden and throwing some plants in there!  You need a greenhouse plan.  These are some of the elements that must be considered in order to really get the maximum potential out of your greenhouse or sunroom: the type of greenhouse you want whether it be a cold house, portable greenhouse, hobby greenhouse a greenhouse kit or a large or a mini greenhouse, the greenhouse construction and it’s foundation type, which greenhouse equipment you will need, which type of greenhouse covering or glazing is best suited to you, and the type of watering, humidity control, heating and air circulation systems that are best suited to your sunroom or greenhouse gardening needs. 

First Decide Whether you Want to have Cold House or a Heated Greenhouse.

A cold house is the simplest of greenhouses, it is not equipped with any artificial means of heat and thus the growing season is shortened when the outside temperature drops below freezing.  It is not possible to grow frost sensitive plants between late fall and the middle of spring unless you provide heat (which would not make it a cold house!).  A cold house does extend the growing season from that of the outdoors by trapping the heat from the sun during the day.   And it provides a cozy respite for you to work away from the elements of wind and rain, it also protects plants from these same elements too.  When you install a heater into your cold house it becomes a true greenhouse and it transforms the hobby of gardening into a year-round hobby.  The minimum temperature required to grow greenhouse plants through the winter is 45° F (7.2°C), so be sure to allow for this extra cost for heating to be included in your monthly budget.  Also, be sure that when you begin planning for your greenhouse construction that you build it as near as possible to your house as this will reduce costs for digging and installation of electrical wires (and plumbing if you need that too).  It is also better for quick access during the winter months if you have your greenhouse closer to your house. 

Choosing between a Portable Greenhouse, Hobby Greenhouse a Greenhouse Kit, Sun Room Kit or a Large or a Mini Greenhouse 

There is truly a wide variety of different styles and types of greenhouses on the market today.  Each is suited to a different need or want and degree of seriousness for greenhouse gardening.  When you build a greenhouse from scratch with a foundation you are probably a serious gardener with great expectations from your greenhouse.  But, for the less serious greenhouse gardener there are smaller versions of greenhouses and sunrooms available that come in the form of portable greenhouses, a hobby greenhouse or mini greenhouses.  Each online greenhouse manufacturer and distributor will have their own specifications and recommendations for each and it is best that you do your own research to decide which is best for you.    

A Greenhouse Foundation is Truly the “Foundation” of any Sunroom! 

A greenhouse is a structure that creates a protected environment for plants to grow in, thus extending the productive lives of plants.  It is therefore important that someone intent upon greenhouse gardening learns as much as possible about maximizing the uses of his or her sunroom.  The first step in greenhouse construction is ensuring that your greenhouse or greenhouse kit will be solid and functional for many years to come is to make sure that it has a good and solid foundation.  It is important to decide whether you want a concrete foundation or whether you want to have a soil foundation.  A soil base in a greenhouse has many advantages, and allows you to grow larger plants straight from the ground.  Just make sure that the drainage in the area that you are going to build your greenhouse is good, and test the soil to make sure that it contains good nutrient rich soil.  If you need to replace the soil, it is better to do so before you begin construction of the greenhouse rather than after!  In order to prevent the floor, or the soil, in your greenhouse foundation from freezing or getting cooler during the winter season it is important to insulate the perimeter of your foundation with a 1- 2 inch Styrofoam board that goes about 2 feet deep all around the outside edge of your foundation. 

The Best Type of Greenhouse Covering or Glazing 

The next most important consideration for the functionality and long term endurance of greenhouses is the glazing that you use.  The glazing is usually the most expensive part of your greenhouse, but this is the feature that will let the very important light that makes your plants grow into your sunroom.  Different types of glazes will give you different growing effects.  The most common types of glazes are plastic sheets or glass.  Most greenhouse kits are easily available at online stores and they come with polycarbonate plastic glaze.  Always make sure that the greenhouse covering or glazing you choose is UV stabilized in order to better protect your plants.  It is important to know whether you are getting single, double or triple thick glaze as you should avoid the single-pane glazes.  Single-pane glass or plastic gets too hot in the summer and too cold in the winter, thus it will not be of much benefit to your greenhouse growing environment.  Double pane or triple pane glazes will suffice much better and will last many years longer. Always remember that cheap upfront can be expensive later on! 

Light and Photosynthesis 

Photosynthesis is the name given to the process that converts light into energy (or into sugar in the case of plants).  In order for photosynthesis to occur the following requirements must be provided: light, a temperature that is optimally between 32°F (0°C) and 100°F (37.7°C), carbon dioxide (CO₂) and water.  The key to greenhouse gardening is to keep all of these factors in optimum balance, and by doing so it is possible to maximize plant growth.  The glazing that you choose to cover your greenhouse can greatly affect the photosynthesis process.  Studies have shown that plants grow better under glass or plastic that is not clear.  Glazings that have smoky appearance to them; that you cannot see through clearly, are advantageous as they scatter the light that enters a greenhouse.  This gives a more even distribution of light and thus gives more total light to plants.  When light goes through clear glass shadows are created in a greenhouse, which causes some plants to get more light than others.

This is an important consideration if you are looking to maximize growth for all plants in your green house.  The best type of material for diffusing light is fiberglass, then polyethylenes, polycarbonates and finally acrylics.  Glass is not good for diffusing light; it is also not as resistant to breakages and temperature fluctuations. 

A Word about Greenhouse Kits and Sunroom Kits 

Greenhouse kits and sunroom kits offer a wonderful alternative for people who don’t have the expertise or the time to build their own green house from scratch.  A green house kit is a new phenomenon of the last few years and because of the fact that most people have very busy schedules these days it is no wonder that their sales are sky rocketing!  They are also very easy to source at online garden stores and are usually cheaper on the internet too.  Most online garden supplies stores offer very good technical support to help you through the greenhouse construction experience!  Most greenhouse kits and sunroom kits are constructed with aluminum, PVC or wooden frames.  Just remember that the reason you bought a kit was probably due to lack of time to build one from scratch, and keep in mind that all outside wood structures need regular maintenance, i.e. staining or painting.  So it is recommended that you buy aluminum or PVC if you want maintenance free!  If you do want to go with an aluminum frame be sure to ask if there are thermal breaks in it, these will make sure that the outside metal is not in direct contact with the inside metal which will help ensure that the inside of your greenhouse stays as warm as possible during the winter months. 

Watering Needs for Greenhouse Plants 

As it does not rain inside greenhouses watering is a very important thing for greenhouse owners to remember!  But, watering inside a green house is not just as simple as just watering your greenhouse plants everyday.  Within soil there are small open air pores that roots depend on for supplying them with nutritious gases.  When you water your plants these small air spaces get filled up with water and it, in effect, causes suffocation for roots.  When roots suffocate, plants wilt and the most common reaction by gardeners for wilting plants is more watering!  Just remember that the watering needs inside a greenhouse are different from the watering needs of your outside garden.  Because the green house environment is enclosed a fair amount of moisture does get trapped and thus, less watering is usually required.  The best rule for watering plants in your greenhouse or sunroom is:  always check the soil before you water, if the soil is dry then you should go ahead and water.  And, remember that plants, just like people, do not like being watered with cold water.  For plants the ideal water temperature is between 65°F and 80°F (18.3°C and 26.7°C).  Anything above 80°F (26.7°C) is too hot! 

There are many different alternatives available for watering your greenhouse plants.  Among your choices are irrigation systems, drip system, misters, water sensors and a gardener’s best friend the good old watering can.  Irrigation systems are wonderful for those periods of time that you plan on being away; there is nothing worse than coming home to dead plants in your green house because your best friend forgot to water them while you were away!  A good selection of all of these watering systems is available at online gardening and greenhouse supply stores.  

Humidity Requirements in a Greenhouse 

All plants have small open pores in their leaves through which gases such as oxygen, and CO₂ pass.  Water vapor is also emitted through these pores as plants do not use all of the water that they soak up.  The accumulation of water vapor is called humidity and relative humidity is the term that describes the quantity of water vapor present in the air.  Air temperature affects the amount of water vapor in the air and it is this relationship between air temperature and the quantity of water vapor present that gives us the term relative; for example: the quantity of vapor present is relative to the current air temperature!  It is possible to measure the humidity of air with an instrument called a hygrometer. 

It is important to know what the humidity is in a greenhouse as most plants grow best between a certain range of relative humidity.  The best range or humidity for green house plants is between 45 and 60 percent.  Knowing your relative humidity also enables you to control your greenhouse growing environment as humidity that is too high (above 80%) encourages the growth of mould both on plants and within your greenhouse.  Plant moulds will destroy plants and will cause rot to occur in any wooden structures within your sunspace (which can be very detrimental if you have a wood frame greenhouse or sunroom or if you have wood shelving or a wood green house bench).  Moulds are also usually a great concern as they cause disease.  

It is more common for greenhouses to have a problem with high humidity rather than low humidity.  If you have a high humidity problem in your green house some remedies are: to increase circulation by installing a fan, water earlier in the day to help prevent evening humidity problems (as moulds grow at night time), water only when the plants need it, buy an air-to-air heat exchanger which exchanges warm moist air with cool and dry air, or put in a ventilation system by which moist air can escape.  If the humidity in your greenhouse or sunroom is too low it is much easier to fix than a high humidity problem.  The easiest and best solution is to water more often.  It is also very easy to buy greenhouse humidifiers that will easily increase your sun room humidity.  These types of humidifiers are easily available at online green house supply stores. 

Carbon Dioxide in the Greenhouse Environment 

My seven year old son came home from school recently and announced “Mom, did you know that trees make oxygen from carbon dioxide?”  It was a great time to teach him a lesson about how plants use carbon dioxide (CO₂) and how they emit oxygen as the end result of this chemical exchange or reaction. 

Since the early 1900’s scientists have been able to measure the amount of _CO2 that is present in the air.  It was discovered that the normal level of carbon dioxide in the air is about 300 parts per million (ppm).  CO₂ is essential to photosynthesis and thus it must be present in the air at least in at least 300 ppm in order for plants to grow properly.  When CO₂ is deficient in the air plants simply do not grow, their growth is very slow and stunted.  It is also actually possible to speed plant growth up by increasing CO₂ levels in the air.  The simple addition of CO₂ to the air is as good as adding fertilizer to your plants.  Most plants grow with a yield increase of ten to thirty percent when the CO₂ levels are between 1,200 to 1,500 parts per million.  Note that anything above 2,000 ppm is not used by plants and it will not increase their growth beyond that point.   

The reason that we need to know about CO₂ is that depletion of CO₂ can be and usually is a big problem in greenhouses and sunrooms.  When plants are raised in a sealed environment as usually happens when you keep all the vents and windows closed in the winters, it is very easy for them to deplete the air of CO₂.  Plants that are raised in our residences have access to the CO₂ that we and our pets breathe out as a waste product and to the air that comes in through open doors and windows.  But, in the crowded plant environment of a sealed greenhouse or sunroom CO₂ can actually be depleted within one day if measures are not taken against this!   

The first action to help with reducing CO₂ depletion for plants in green houses is to realize that a plant produces oxygen through it’s leaves, and the oxygen actually sits on and around the leaves unless the gentle breezes of nature comes by and blows it away!  Then the leaf pores are introduced to the CO₂ that the breeze just circulated to them and they are able to access it as the oxygen is no longer “blocking” their pores.  We know, of course, that nature’s gentle breezes do not enter sealed greenhouses!   Thus, we need to create some type of a “breeze” system within our greenhouses to circulate the oxygen away from the leaf surfaces and introduce the CO₂ that is in other areas of the greenhouse.  The simplest way to do this is to introduce a fan to your green house or sun room; either a floor fan or a ceiling fan works very well!  Note: that you can turn the fans off at night as plants do not utilize CO₂ in the absence of light.   

A second step is to consistently introduce organic matter to your soil as the microbes and bacteria in decomposing matter is living and breathing and provides the air with it’s waste product; which just happens to be CO₂!  The amount of CO₂ that organic matter introduces can also be depleted quickly, so the installation of fans is still necessary.  It is also interesting to note that some people with a bigger greenhouse space that permits the keeping of a rabbit in a hutch or chickens in a cage will do so in order to supply their greenhouse plants with extra CO₂!  The most important thing to remember here is that you will need to allow for the extra work of cleaning out a rabbit hutch or a chicken cage as they get quite smelly quickly and the excess ammonia in the air will not be good for your plants or pleasant for you either!  So if you’ve ever entertained the idea of having a pet rabbit for either you or your kids this may be your chance providing you are prepared to clean out a cage about once every 5-8 days.  (or this could be a great opportunity to teach an older child some responsibility and add a chore to their list!) 

Proper Balance of pH Levels for Maximum Greenhouse Plant Growth 

Healthy soil is required for good plant production and healthy soil is created when it has a proper pH!  There are a few aspects to creating and maintaining healthy soil and a proper pH balance.  If the pH level is off balance then it is impossible for the critical nutrients necessary for plant health to survive in soil.  The pH describes what the level of acidity is in your soil.  The pH scale is based on a scale of 1-14, with 7 being the mid-point or the neutral point.  Soil that is from pH 0 to pH 7 is considered acidic, and soil that is from pH 7 to pH 14 is considered alkaline, or basic.  It is best to keep your soil as close to 7 as possible. 

Greenhouse gardeners are wise to test the pH levels in their soil and pH test kits are easily available at online green house supply stores.  If your soil is too acidic (low pH) it is best to add limestone or wood to your soil, and if it is too alkaline (high pH) it is best to add compost material (avoid manure), sulfur or acidifying plant foods that are available commercially.  A properly balanced pH will ensure that the correct nutrients are available for your plants to properly root and utilize the minerals in the soil that are required for maximum growth.  It also ensures that the healthy and beneficial microbes that live in soil can survive and help plants grow.  Healthy microbes are important in controlling diseases and they also feed on bad microbes such as parasites too.  When good microbes cannot survive in soil the bad microbes will take over and thus there is a greater chance of disease and pests entering the greenhouse environment.   This is not unlike the good bacteria/bad bacteria that live in the human bowels, we need to keep these in balance too in order to prevent disease from entering the human body! 

Heating Needs in a Greenhouse 

Scientists have proven that the optimal growing temperature for most plants is between 50°F (10°C) and 85°F (29.4°C).  This is a big temperature range and your consistent temperature target is really dependent upon the type of plants that you are growing in your greenhouse.  If you have mostly seedlings then it is useful to note that seedlings thrive in warmer temperatures.  If you have mostly mature plants then aim for a cooler temperature target.  If the temperature gets above 85°F (29.4°C) then you will get plant growth problems such as slower growth and flower drop which will prevent flowers from setting and producing fruit.  If temperatures get too low you will see much of the same problems as when the temperature gets too high.  Temperature is vitally important to plants as it affects everything in their life cycle; photosynthesis, cell division, water intake, nutrient uptake, etc.  It is thus, vitally important that we manage the temperature in a greenhouse so that we can assist our plants to grow at their maximum potential.   

Here are four ways to supply a heat source to greenhouses; portable heaters, hot water pipes, wired in electrical heat or solar heating.  Each has their own benefits and each has their downfall!  Portable heaters are a wonderfully quick and easy way to add heat to a greenhouse or sunroom; they can be powered by natural gas, electricity, propane, wood, oil or kerosene.  The biggest downfall with the gas, oil, wood or kerosene heaters is that whenever you burn them they emit gases that are harmful to plants so you absolutely must have some kind of a ventilation system that carries these emissions away and out of your greenhouse.  Be careful that your venting system is not in direct contact with the skin on your greenhouse if it is made out of plastic as the heat from the ventilation system can melt the skin or in cases of excessive heat could actually cause it to melt!    Also, check on the recommended size of heater for the size of your greenhouse.  Most manufacturers will give you a recommendation for the maximum and minimum heating space that their heaters will heat. 

Hot water systems are best installed by professional welders and plumbers.  They are often custom made to fit the size of your greenhouse and usually consist of a system of pipes that run around the inside walls of your sunroom.  They are attached to a water intake system and a pump that circulates the water through the pipes.  Although the initial heating of the water in the pipes is a little costly, once the water in the pipes is hot it retains its heat very well which is where the cost reduction in hot water systems comes into place.   

Electric heating in a greenhouse is an amazing concept in “how to very easily heat a greenhouse” – you turn the dial!  The only problem is that electric heat in a greenhouse can get very, very expensive in the winter.  The other major problem that you need to consider with electric heating is what your back up plan will be if there is a power outage.  Remember that if you lose power in the middle of a winter freeze you could actually lose all of your plants overnight!  The best device for “watching” greenhouse temperatures is a ‘temperature alarm’ that is made specifically for greenhouses.  This nifty little device will set off an alarm as soon as the temperature in your greenhouse or sun room goes below a level that you preset into it.  When this happens you will know that either your power has gone out or you just need to turn up the heat!  In cases of power outages perhaps the best back up plan is to purchase your very own generator that can power a portable heater or two inside the green house or sunroom until the power comes back.  Another very wise investment is to purchase some solar heating panels for your greenhouse, these will generate enough heat through a power outage in the winter to prevent freezing, although they will not usually generate enough heat to keep a greenhouse warm through a long freeze.  Solar heating panels will prevent you from losing the majority of your plants in a short power outage during a freeze.

Solar heating is a very cost efficient way of heating your greenhouse if you set it up properly and design your green house to use solar heating efficiently.  The most important thing to consider when first designing your sunroom or green house construction is to decide upon it’s location in your garden.  To maximize the usage of the sun’s energy it is best that you orientate your greenhouse to have its long side face within 20 degrees of either side of true south.  And in order to utilize larger solar panels it is best to have the greenhouse be 2 or 3 times longer than it is wide.  Other ways to ensure solar heating is maximized is to make sure your greenhouse is airtight, so that it doesn’t lose it’s heat through leaks.  Make sure that your glaze is double or triple glazing to help reduce heat loss.  Insulate the walls of the greenhouse to prevent heat loss, this is especially useful on the north wall where most heat loss will occur; and the easiest way to insulate this wall is to buy bubble insulation in rolls (the kind of bubble wrap that packages come wrapped in for protection in the mail).  Some green house supply stores carry clear bubble greenhouse insulation. Spray a glue adhesive to the inside of your glazing and press your pre-cut bubble insulation up against the adhesive until it sticks.  Earlier in this article we talked about insulating the foundation of your greenhouse with 1-2 inch thick styrofoam board, and this is another way to prevent heat loss from your greenhouse – especially if you choose to go with solar heating panels.

Selecting the Right Seeds and Plants for Your Greenhouse

When it comes to selecting seeds and plants for your greenhouse the biggest deciding factor is your personal choice!  You will need to set up your greenhouse interior to accommodate the types of plants that you choose though.  For example if you choose to grow plants that require a trellis you will have to install some trellises.  Some examples of plants that grow well with a trellis are peas, runner beans, tomatos, cucumbers, watermelon, winter squash, nasturtiums, passionflower, bougainvillea and sweet peas.  Some crops are harvested only once and then they are done; for example onions, carrots and radishes.  Other crops that need harvesting many times; for example leaf lettuce,  strawberries, broccoli and brussel sprouts should be placed in easy to reach places, like at the edges of beds.   

Buy a good book on greenhouse gardening so as to learn about the different temperature, water, humidity and pH level requirements of different plants and then make your final selections of seeds and plants.  A greenhouse gardener’s book will also help you with the best layouts for your plants and seedlings. 

As a final note on buying seeds and plants for your greenhouse please be aware that it is very advantageous to buy them from online greenhouse supply stores and online seed catalogues as they are coming directly from “the source” in most cases!  This means that the seeds and plants are usually fresher and have been stored correctly while in storage as a lot of online stores are based directly from farms and growing facilities.  The selection and varieties of seeds and plants that are available at online stores are unequalled.  You will be delighted with the selection and the information that is available for each plant or seed selection that you choose at online green house supply stores and seed or plant catalogues.  Customer service at these stores is also exceptional.  Most online gardening stores offer free shipping once an order hits a certain dollar amount too!

Buying a Green house is Investing in a Therapeutic Activity!

There is nothing like “getting down with the dirt” to really melt away the stress of a busy day.  Gardening is a cleansing and therapeutic way to spend your time, it enables us to get in touch with nature, and it’s no wonder that it is one of the most popular leisure activities that people list in their resumes and on questionnaires.  I have a doctor friend who advises his patients to run barefoot on the beach to unwind and let stresses melt away, I find that gardening and greenhouse gardening does the same thing for me! 

If you invest some time in researching greenhouse construction, types of greenhouses and sunrooms available such as greenhouse kits, sun room kits, hobby greenhouses, large or mini greenhouses and portable green houses you will be sure to start an adventure of a lifetime!  Remember to learn all that you can about greenhouse equipment, which type of greenhouse covering or glazing is best suited to you, and the type of watering, humidity control, heating and air circulation systems that are best suited to your sunroom or greenhouse gardening needs.  Time invested in greenhouse gardening before you actually start your green house construction will be time well spent, and will ensure that you get maximum stress relief and enjoyment out of your greenhouse hobby!!

About the Author

Julia Mahler is a successful and talented freelance writer providing advice for gardeners and consumers on purchasing a variety of garden supplies which includes greenhouse kits, garden sheds, decorative house numbers, outdoor patio furniture, decorative birdhouses, pond kits and more! Her numerous articles provide a wonderfully researched resource of interesting and relevant information for all of your gardening needs.

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