Garden & Greenhouse


Going Green with Your Greenhouse

Posted May 4th, 2016 by Garden & Greenhouse in ,

Going green is in. Movie stars arrive to the Oscars in hybrids. Politicians claim green industries will save our economy. Large chemical companies stick pretty labels on products, call them green and hope to hit pay dirt. Green is the holy grail of marketing. So what does going green really mean? Green washing (a disingenuous claim to environmental benefits) is to advertising as white washing is to a blazing hot glass greenhouse: a superficial, temporary, and ineffective fix.

Finding green solutions is not just eliminating the use of pesticides, or calculating the carbon footprint of this or that. Finding sustainable solutions requires thinking about a longer time horizon than the here and now. That’s not easy in our disposable society. But making decisions that are good in the long term often turn out to be good for the pocket book.

Purchasing a “Green” Greenhouse

Whether you are looking to save the planet or to save money, the first place to start is the greenhouse. There is a rise in popularity of inexpensive greenhouses. While this may seem like a boon to the budget, many of the less expensive greenhouses are inexpensive because they are cheaply made. Not only is the idea of a “throw away” greenhouse not so green, it could cost you dearly. Many people don’t think about what will happen in the first wind storm. Picking up pieces of a greenhouse around the neighborhood isn’t green and can cost a pretty penny. On the upside, if you lose a poorly made greenhouse to a wind storm, the disposal is a bit easier than dismantling the unit yourself. That’s probably not the benefit you were looking for.

You don’t have to spend a fortune on a greenhouse, but buying quality up front will save money in the long run. You may not know how many years a greenhouse will last, but the warranty period is a good indicator. Divide the purchase price by the warranty period to determine the yearly cost of ownership. Once you know the yearly cost, you will also want to consider the costs of disposal. Don’t forget the value of your time; you probably won’t want to rebuild another greenhouse in two or three years.

It is possible to recover some greenhouse frames if there is a problem with the covering. Salvaging a greenhouse can be a huge cost savings. If the greenhouse frame cannot be recovered when the “skin” wears out, you will be spending time, money and gas making a trip to your local landfill. That’s probably not a trip you will want to make often.

One final consideration in the purchase of a greenhouse is where and how the greenhouse is made. Like most of the products we consume, the majority of greenhouses available on the market today are made in China. There is no way of telling what additives may be included or excluded in some of these products. At a recent trade show I saw 4 mm twin wall polycarbonate that literally rolled like paper. Some products are designed to be flexible; polycarbonate is not one of them. It is a common, but unfortunate, practice to add inexpensive fillers in production to reduce costs.

It is up to you to determine if the cost savings outweigh the lax environmental and quality control standards found abroad. If you are in the market for a greenhouse, look for a supplier that knows the greenhouse well and can answer your questions about the products. Finding a knowledgeable company will go a long way in helping you choose a quality product. If the sales person has not used, assembled or spent time with the greenhouses, proceed with caution.

So what do you do if you already own a greenhouse but you tried to save a little too much money? Stay tuned. In 2010, we will talk about ways to salvage, or at least improve, a greenhouse purchase mistake.

Green Operation

Heating and cooling a greenhouse require the most energy. If you have a greenhouse made with a single layer covering, whether it is made of glass or thin plastic film; forget heating as a cost effective or green solution. Heating anything with a single layer covering is hardly different than heating the air. It won’t be easy on your pocketbook, and it certainly won’t be green. If you have a single layer covering on your greenhouse, don’t send it to the landfill yet. It may also be possible to cover your existing greenhouse frame with an insulated material if you plan to heat it. Even if you don’t add heat, single layer structures make for great cold frames. They keep the frost away and protect plants from harsh and damaging winds and rain. With a cold frame it is easy to start a few weeks before your local frost date without heat.


Insulation is the key to efficiency. An average thermal pane window has an R-value of 2.5. A greenhouse made of 4mm polycarbonate has an R-value of 1.4 and will use nearly 75% more energy than heating a room of windows. The greater the insulation, the more efficient heating and cooling will be.

Greenhouses are one of the earliest forms of solar collection. Harnessing the sun’s energy for use later is the epitome of employing natural and renewable sources of energy. Trapping the heat inside with good insulation extends the natural growing cycle. Extending the natural growing cycle means plants absorb more carbon dioxide and produce more oxygen. It also means you have more home grown food, more landscaping plants and more enjoyment.

Adding Heat

If you have an insulated greenhouse you would like to heat, there are a few options: electric heat, natural gas, and propane. You may choose a heat based solely on your access to resources. Choosing a heater with a thermostat or frost setting is an excellent choice for areas where you are trying to maintain above freezing temperatures. Spot heating with seedling heat mats or heating cables are a good choice for sensitive plants. Heating the air in the greenhouse is costly and inefficient; Soil, water, or other mass will retain heat much longer.


Cooling a greenhouse is another important consideration. One hot spring day spells disaster for a greenhouse with inadequate ventilation. The same principle that makes heating greenhouses efficient makes them difficult to cool if too much light enters the structure. Clear greenhouse covering requires significantly more resources to cool. White washing, applying diluted white paint, was a common practice with glass greenhouses, but will not work with most modern materials. Shade cloths are a good alternative to white washing as they cut down the amount of light entering the greenhouse.

New solar powered fans are a good solution to cooling. By using the sun’s energy to power the fans, excess heat is removed from the greenhouse. The drawback to the solar fans, however, is the inability to track the sun’s path in the sky. Solar powered fans are not effective as the sole means of cooling, but can work well to supplement other methods. The Aluminet shade cloth is an excellent choice for shade cloth. The reflective surface does not absorb excess heat as the black cloths do so it will keep the greenhouse a few degrees cooler.

Keeping doors and vents open in summer will add a breeze and cool the greenhouse, but more may cooling be needed. Summer is the perfect time to move plants outdoors. If you are unable to move plants outside, open the doors and vents, add shade cloth, and spray water on the floor in the mornings. The evaporating water will help cool the greenhouse.


It is not necessary to add grow lights to a greenhouse unless plants require longer daylight hours to prosper. Without longer days, plants may not bloom or produce but many will survive until the daylight lengths increase naturally. One way to save costs and reduce power consumption is to group light-seeking plants together. Clustering plants together with longer photoperiods will reduce the total lighting requirements. Additionally, consider using either fluorescent T-5 or LED lighting. Both of these types of light produce good results with a fraction of the energy. Adding a simple timer to the lights to create the day lengths desired will save considerable energy. Most plants require at least 6 hours of darkness.

Reduce Water Requirements

With many municipalities implementing strict and expensive water policies, saving water can have a huge impact on the resources used. Plants in containers are much more subject to drying out. The large surface area of containers leads to evaporative loss and often requires substantially more water than plants that can retrieve excess water from the ground. Choosing a soil mix containing coir fiber, or adding it yourself, significantly reduces watering needs. Look for mixtures containing coir fiber versus peat moss. Peat is a diminishing resource and it quickly sheds water if allowed to dry out at all. Watering each container slowly and individually will also conserve water. Slow deep watering is absorbed better than a quick drenching. Watering slowly requires more time, but there are some interesting and low-tech drip systems that work well in greenhouses. These systems are a good solution for busy gardeners.

Pest Control

Insect problems in a greenhouse can quickly become an infestation if not managed properly. There are several natural and non-toxic methods for controlling insects, but none are as effective as prevention or tackling the problem as soon as it arises. Practicing good greenhouse hygiene eliminates many pests and diseases. Removing all dead plant material quickly and regularly removes the habitat for infestations. If you find unwanted pests, immediately remove the affected plants. It may be difficult to part with a favorite plant, but it may prevent the problem from spreading quickly.

If you find you have a problem, determine what insect is the cause. The appropriate treatment depends on the offender. There are many organic insecticides but organic does not mean non-toxic. Ideally, choose sprays that are safe enough to harvest the fruits the same day as sprayed. A few examples of sprays include: neem oil, pyrethrins derived from chrysanthemum plants, Chili sprays or garlic.

Avoid sprays altogether by introducing beneficial insects that prey on the pests. Lady bug larvae consume large numbers of aphids keeping populations in check. There are many types of beneficial insects ranging from invisible nematodes to 3 inch praying mantis.

Working With, Not Against Mother Nature

Zonal denial fuels many greenhouse desires and is one of the primary rewards of owning a greenhouse. Eat the first ripe tomatoes on the block, overwinter a favorite plant, or eat salad from your greenhouse in the dead of winter. All of these things are fairly easy to do when you work with, instead of against, the seasons. Operating a green greenhouse means starting spring earlier than you normally could and enjoying fall into the first winter months. You can grow outside your zone by taking cues from mother- nature; planting warm crops in summer months and cool crops in winter. Planting heat and light loving plants in the dead of winter require much more heat and light than cool crops.

If your goal is to protect specific plants that require a warm climate, create a micro-climate in the greenhouse. Add heat to the plant instead of heating the entire greenhouse. Wrap a string of Christmas lights around a container to protect sensitive roots on a cold night. Cover delicate foliage with a frost blanket to protect leaves from the cold air.

We are bombarded with techniques and messages about living a greener life. As gardeners, we are more connected to the earth than most, and we tend to take this message to heart. There are many small steps we can take to create a better world. Luckily, many of those steps in the greenhouse are money saving techniques. Purchasing and operating a greenhouse is an investment that should yield high returns for years to come.

Michelle Moore is the General Manager of the Greenhouse Catalog where she has worked with greenhouses for 20 years. Michelle writes and lectures about greenhouse gardening as an Oregon State University Master Gardener and member of Garden Writers Association. Michelle is a Fulbright Scholar and earned an International MBA from Thunderbird, School of Global Management.