Unlock new growing opportunities and increase your property value with an outdoor conservatory. In this illustrated guide, Roger Marshall shows you how to build our own greenhouse using simple, easy-to-follow techniques. Covering everything from selecting a site to glazing glass, Marshall includes tips on laying a foundation, construction materials, ventilation, and much more. Whether your goal is to stretch the growing season or create a lush space for a year-round hot tub, you can build the greenhouse of your dreams.
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About the Author
In addition to designing boats, Roger Marshall regularly lectures and gives talks on gardening and greenhouse growing. He writes a monthly blog post for Hartley Greenhouse, and is the former editor of Home Greenhouse. He is also a member of the Garden Writers Association, The American Society of Journalists and Authors, and the Society of Authors (UK).
Read an Excerpt
Questions to Ask before You Begin
IT'S WINTER and a snowstorm has deposited a foot or so of the white stuff everywhere. With the departing of the storm, the sun is shining on a beautiful cold, white landscape. As you scrape the snow off your greenhouse roof, you feel like heading south to warm weather so you change out of your winter clothes and walk into the greenhouse abutting your home.
Inside, the temperature is almost 80°F, the humidity is high, and a waterfall is babbling into a pond. Green plants and flowers send their aromas your way. Everything is right with the world. No need to fly south. You have a choice of climates without traveling beyond your own home.
Sound too good to be true? It's not. As I write this in the middle of December in Rhode Island, the door from my studio into the attached greenhouse is wide open. Outside, the sun is shining brightly. Warm, moist air floods my studio from the greenhouse, where the thermometer reads 78°F. Impatiens, geraniums, and fuchsias are in bloom. In a week or so, paperwhites will also be in flower, adding their powerful fragrance to the other scents in the air. Outdoors, I have to trudge through the snow, but in here it's warm and tropical. A greenhouse exists to create a microclimate in which plants can grow, people can stay warm, fish can be raised, and the sun's heat can be harnessed and distributed. In other words, with a greenhouse you can keep a little bit of summer within easy reach year-round.
In this chapter we'll look at the first questions to ask and the primary considerations as you explore constructing your own greenhouse. In many cases, these go hand in hand with determining how you plan to use your greenhouse (see chapter 3).
How Much Time Does a Greenhouse Require?
You can spend as much time as you want or can afford to spend in a greenhouse, but if you are like many of us, you have many things that need doing and your time is limited. From my experience working in them, I've found that greenhouses do need tending fairly often. Beyond necessary time, you may be lucky enough to free up many more hours to spend among the plants in your greenhouse.
I find that my greenhouse chores require a few hours per week, depending on the season. In spring, for example, the greenhouses are packed with flower and vegetable seedlings. In the middle of January, I generally spend three or four nights setting up seedling trays and starting plants in the germination chamber (see A Germination Chamber or Seed-Starting Box for information on how to build your own). After the plants have germinated, I spend about half an hour each day watering, fertilizing, and adjusting the lights. By the end of February, I move these fast-growing seedlings into the heated greenhouse under grow lights (which provide enough light to prevent the plants from getting leggy). I check and water them there every day, which takes about an hour. In late fallor early winter (December or early January) I also spend a few hours each week in the greenhouse potting up hanging baskets and tending the plants I propagated in the early fall. During the winter, I spend 1 or 2 hours a week in the heated greenhouse.
Schedules can be individual, however. I have a friend who owns a heated greenhouse and she can spend almost an entire weekend just puttering around in it. She tells me that her husband complains that she spends too much time there. For many people, the amount of time spent in a greenhouse varies dramatically depending on the time available.
For about two months during the summer, my heated greenhouse usually stands empty, although I might keep in it any expensive plants that could be gnawed by squirrels or deer and plants that need a little more heat than that provided by normal summer weather. This is the time when I paint and do routine maintenance with the structure's windows and vents open. During this time, I plan what will take place in the fall.
Around late August or early September, I move back into the greenhouse all plants I placed around the deck and property for the summer. This can take one or two weekends. I thoroughly check each plant and spray each one with pesticide. (I prefer to use an organic pesticide such as Safer's insecticidal soap. I spray each plant twice about ten days apart to eliminate any newly hatched insects.) I repot some plants and lightly fertilize all of them. Once the plants are under cover, despite the spraying, insect explosions may occur (some eggs may be missed and sometimes insects can hitch a ride in the potting soil) and these will need to be treated, so I spend 30 minutes to an hour each day checking plants and treating problems.
By early November insect infestations, late growth spurts (from plants just been moved into a warm greenhouse from the cooler outdoors), and other modulations have settled down. Now shortening days, limited light, and cool temperatures slow plant growth, so fertilizing and watering slow too. By late December, I might go into the greenhouse only twice a week for an hour or two to water and check plants, looking for insect problems, removing yellowing leaves, cleaning up any leaves that have dropped, and simply making sure that everything is as it should be.
My unheated greenhouse works on a different cycle from the heated one. During January and February, our coldest months, it holds little except for Chinese greens, spinach, herbs, and other hardy plants that we use in the kitchen. I use this time to dig over the beds, adding compost and manure to them, and to repaint the inside of the greenhouse or make any needed repairs to the interior structure. Come March, the beds contain greens and peas started in the basement germination chamber. These can take the freezing nighttime temperatures. As soon as I harvest the greens, in middle to late May, I refresh the soil and transplant tomatoes, peppers, melons, and eggplant seedlings into the growing beds. By this time, I've moved the greens and peas outdoors and the brassicas are about to be transplanted from the cool greenhouse as well. During summer, when everything is growing, I spend a couple of hours each week in the cool greenhouse, weeding, tending plants, and watering.
The heated greenhouse, which is usually empty during summer, may need painting and maintenance work during that season. Because I work at home on the property, I can manually open and close the windows and vents as required, which takes a few minutes each day, but this is a chore that can easily be automated. Whenever possible, I perform maintenance on the exterior of the unheated greenhouse because it's in use in all but the coldest months.
On average, I'd say that half a day each week year-round is a fair estimate of the time required to run and maintain a single greenhouse. Once you have a greenhouse, you will adopt a routine and adjust your schedule to suit its requirements. In general, assume that you will spend at least an hour a day there from spring to midsummer, although you might combine these on the weekend instead of spacing them out over each day. In winter, you probably won't spend more than an hour a week in the greenhouse. Ofcourse, you may enjoy the heat and humidity of a warm greenhouse on a sunny day, and on those days, who knows how much time you'll spend in there? For more on greenhouse maintenance schedules, see chapter 12.
What Is Your Budget?
In your final greenhouse decision, budget is often the controlling factor, determining size, materials used, whether or not you can heat your structure, and, thus, how you'll use it. If you want large, you can scale back considerably when it comes to materials and heating systems. Because I wanted large greenhouses, I made mine out of low-cost recycled materials. In my original cold frames, for instance (where heat wasn't an issue), I used old storm windows. Later, in sizable structures, I recycled old windows by using panes of double- glazed glass with broken seals. The broken seals meant that each side of the double glazing could be used as a single pane. I became such an avid collector of old glass that one time a local store called me and, for the price of removing them, offered me double-glazed windows that were going out of stock. Using these panes, I built a 30-foot by 10-foot lean-to greenhouse. The lesson here is that the cost of a large greenhouse need not be very high if you're willing to get creative with the materials you use — which may also mean rethinking how you want to use the structure.
In determining your budget, take into account such factors as the cost of the foundation, glazing, plumbing, wiring, and landscaping. Part of your budget equation should also include the cost of operating a greenhouse, such as lighting needs, heating it in the colder months (if you plan to use it during this time), and cooling it in hot weather. If you build a greenhouse that is bigger than you can afford, you may end up not using it because it costs too much to heat, cool, and light the structure. By planning your budget before you build and knowing what you can afford, you'll get more enjoyment out of your greenhouse and have money left over for plants. The Checklist for a New Greenhouse will help you in the process of determining your budget. In addition, the table on page 7 rates various elements of greenhouse construction by cost.
How Large Should Your Greenhouse Be?
As explained above, one way of determining the size of your greenhouse is to base dimensions on what you can afford to build and heat. Before building, you should find out how much it will cost to heat the structure you are considering. I know of one greenhouse owner who built a large greenhouse without predetermining the heating cost and found that she spent almost $700 per month to heat it in the middle of winter!
One way of determining the size of your greenhouse is to base dimensions on what you can afford to build and heat.
This heating caveat aside, though, if you are an experienced gardener, make your greenhouse just as big as you can. You will fill it with plants. I built a 280-square- foot greenhouse, then decided that it needed to be heated. Now it is full of tropical plants and even has a fishpond. It is so full that during the winter months I find it is difficult to move around inside. I've since built a second 280-square- foot greenhouse for growing vegetables. It has served well, but I have a strong urge to set up a heated growing bed or two and add heat to this structure. I also use an unheated, plastic-covered hoop house to extend the growing season and to protect winter greens from deer and rodents. That's how it is with greenhouses — once you start, who knows where you will end up?
If, however, a large greenhouse seems daunting, you might want to build or buy a hobby greenhouse that is 8 feet by 10 feet or 8 feet by 12 feet. If you don't want to heat it, you can use it simply to extend your season in the spring and fall. Another way to begin greenhouse gardening without investing in a sizable structure is to try using cold frames and other small season extenders (see Small Season Extenders and the cold-frame project in chapter 13). These can be only about 4 feet by 4 feet — a manageable size. Through these smaller structures, you may find that you enjoy pushing the limits of your growing season and that you'd like to put some cash and effort into buying or building a larger greenhouse.
Another way to begin greenhouse gardening without investing in a sizable structure is to try using cold frames and other small season extenders.
In determining the size of a structure that's right for you, remember that the larger the greenhouse, the easier it is to maintain a constant temperature inside it. The mass of air inside a large structure takes longer to heat and cool than that in a smaller structure, thus a large greenhouse helps moderate the swings between soaring temperatures on hot, sunny days and abruptly cooling temperatures at night. Conversely, the smaller your greenhouse or cold frame, the more quickly it will both heat up and cool down. In fact, without venting of some kind, smaller structures can overheat very quickly.
See chapter 4 for more on the factors that will help you decide on a size that's right for you.
What about Structure and Systems?
In tandem with determining your budget, you'll need to consider structural elements (such as building materials, glazing, and heating). See later chapters in this book for more detailed information on each of these components.
Also important to consider are the structural materials used to build the frame of the greenhouse. They should be strong yet light. Aluminum framing meets both requirements, but it also transfers heat out of the greenhouse via the metal. Wood framing takes up more space than aluminum framing and cuts down on the amount of light that enters the greenhouse — but it does allow less heat loss than aluminum. You'll need to balance these structural factors when you choose your greenhouse frame.
For more on structural building materials, see chapter 6.
Light and Glazing Options
Generally, plants in a greenhouse require plenty of light. In most cases, the easiest way to get enough light in the greenhouse is to make sure the structure is located where nothing is obstructing sunlight. In addition, the orientation of your greenhouse and the placement of its glazing can affect light exposure: If you plan on growing in midwinter, for instance, you'll need to make sure that your structure's glazing is at or near a right angle to the sun's path. This allows more light to pass through the glazing and less to be reflected away from it.
The type of glazing you use also affects the amount of light that gets to your plants. Single-pane glass, if kept clean, allows the most — about 96 percent of the total light available. But single-pane glass is both heavy and expensive, and if you drop a pane, it makes a real mess. In addition, there are certain building requirements that must be met for glass in different areas of the country. Some jurisdictions require the glass to be hurricane-proof or tempered and others require all installed glass to be safety glass. You'll have to check your local building codes before you plan your structure.
If your plants don't require maximum light, you have other options for glazing: acrylic or polycarbonate panels, polyethylene sheeting, fiberglass sheeting, and corrugated fiberglass sheeting. They all differ in the amount of light they allow into the greenhouse and each provides certain benefits and drawbacks in cost, installation, and other areas. (See chapter 7 for more on glazing options.)
Freestanding greenhouses can be heated or unheated, but an unheated greenhouse glazed with single-pane glass may not be usable for the coldest part of the year north of the Mason-Dixon Line. Depending on its size, location, and time of the year, an unheated greenhouse has a nighttime temperature of about 8 to 10 degrees F above the surrounding area. This means that in your greenhouse you can grow plants that would survive in one USDA plant hardiness zone warmer than your area. In other words, if you live in Zone 6, in your greenhouse you can support plants that would survive outdoors in USDA Hardiness Zone 7; you can use the frost dates for Zone 7 to determine dates for growing plants in your greenhouse. By contrast, sunny daytime temperatures in a greenhouse can climb to 50 to 60 degrees warmer than the surrounding area. For example, on a sunny day, the temperature in my single-pane unheated freestanding greenhouse is 75°F to 85°F when the temperature hovers around freezing outside and there is snow on the ground. (Refer to the USDA Hardiness Zone map.)
Though you may have a use for your greenhouse in mind as you begin to plan, consider whether you can afford to (or want to) heat the structure. Heating costs can vary widely, depending on the size of the structure and the kind of system you use. (For more on heating a greenhouse, see chapter 5.)
What Are the Pros and Cons of Kit Greenhouses?
A major consideration at the start of your planning is whether to buy a kit greenhouse or build your own structure from scratch. With the introduction of aluminum framing, polyethylene film, and galvanized steel, kit greenhouses have become affordable for everyone. Hobby or kit greenhouses can be made of wood, steel, extruded aluminum, or PVC, with glass, acrylic, polycarbonate, or even polyethylene sheeting as glazing.
A hobby greenhouse is the most basic kind available and can be purchased from a home or garden center or through any of the company Websites listed inResources. If you order a simple, smaller model (which may require a foundation), you can assemble a kit greenhouse yourself, while larger models (which will require a foundation) are usually assembled by a contractor. There are hundreds of retailers of kit and hobby greenhouses, which range from the simplest PVC pipe–frame greenhouses to elaborate wood- or metal-frame buildings. In general, less expensive styles are usually freestanding and single-glazed with a door at one end and one roof vent. As the price goes up, so do the options and the construction quality.
Excerpted from "How To Build Your Own Greenhouse"
Copyright © 2006 Roger Marshall.
Excerpted by permission of Storey Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
1. Questions to Ask before You Begin
How Much Time Does a Greenhouse Require? What Is Your Budget? How Large Should Your Greenhouse Be? What about Structure and Systems? What Are the Pros and Cons of Kit Greenhouses? Build It Yourself or Hire a Contractor? What Aesthetics Are Important to You?
2. The First Glasshouses
The Start of Growing under Glass * The First Conservatories * Orangeries and Pineries * Nineteenth-Century Colossal Greenhouses * The Hobby Greenhouse
3. An Overview of Greenhouse Options
What Type and Structural Style Do You Want? * Five Basic Types * Basic Structural or Building Styles
4. Choosing the Greenhouse Site, Size, and Interior Layout
Site selection * Determining the size of your greenhouse * Making the floor plan * Designing the entrance * Getting permits
5. Controlling the Greenhouse Environment
Water in the Greenhouse * Lighting and Electricity in the Greenhouse * Heating, Cooling, and Ventilation Systems * Hydroponics * Insecticides in the Greenhouse
6. Greenhouse Building Materials
Wood as a Construction Material * Sheathing * House Wrap * Exterior Siding * Other Greenhouse Framing Materials * Framing Materials Insulation * Vapor Barriers * Doors * Alternative Building Materials * Painting the Greenhouse
Understanding Light Transmission * Types of Glazing Materials * Combining Glazing Materials * Caulking and Weather Stripping
Checklist for a New Greenhouse
8. The Foundation
Types of Foundations * Types of Floors * Constructing a Concrete Foundation and Slab * Finishing the Foundation
9. Building Techniques
Building a Kit Greenhouse * Building a Conventional or Do-It-Yourself Greenhouse
10. Wiring, Plumbing, and Heating: Systems Design and Installation
Installing Electricity * Installing Plumbing * Installing a Heating System
11. Greenhouse Accessories
Benches * Shelving * Growing Beds * Tools and Equipment * A Germination Chamber or Seed-Starting Box * A Growing Chamber * A Potting Bench * Storage * Greenhouse Clothing * Accessories to Control Insects
12. Greenhouse Maintenance
Regular Chores * Monthly or Quarterly Maintenance * Biannual or Annual Maintenance
13. Greenhouse Plans
Basic Conventional Greenhouse
Slant-Front, Insulated Greenhouse
Gothic Arch Greenhouse
Greenhouse Built on Piers or a Deck
Hoop House or High-Tunnel Greenhouse
Multiuse Cold Frame