For avid gardeners, passing the long months between the first frost and the spring thaw is hard. Even for gardeners who enjoy mild temperatures year-round, pests or flooding can cut the growing season short. No wonder many gardeners have embraced greenhouse gardening.
Greenhouses make it possible to grow flowers and food year-round. It also gives gardeners a chance to control their plants’ environment. With consistent temperatures, moisture, and protection from the elements, greenhouses offer a world of possibilities.
Just getting started with indoor growing? Read on to learn all about greenhouses and plan your own greenhouse gardening.
What is a Greenhouse?
Greenhouses are structures designed to maximize sunlight to heat the plants inside. The walls and roof are made of transparent materials, usually glass, to let in the light from every angle. The structure itself is completely enclosed to trap in heat.
While many of us picture greenhouses as large, walk-in glass houses, the principles of greenhouse gardening apply to any size structure. You can still use a greenhouse if you have an apartment balcony or a small yard! Some greenhouse kits are the size of small cabinets. You can also add a temporary cold frame to your garden bed during winter.
The structure and size of your greenhouse depends on how you plan to use it. Large, permanent structures can be used for growing food year-round. If you simply want to overwinter delicate plants, a small greenhouse structure or temporary cold frame will do.
Setting Up Your Greenhouse
Choosing a Location
Before building your greenhouse, evaluate the amount of natural light it will receive throughout the day. Observe the area throughout multiple seasons, if possible.
Deciduous trees can block substantial light during the spring and summer months. Nearby buildings can cast long shadows that change from one season to the next. Your greenhouse garden will be most efficient if it’s in an area that receives consistent, direct sunlight.
Next, consider how you will secure the entrance of the greenhouse. Greenhouse design depends on successfully trapping heat, so opening and closing the door will cause temperature fluctuations. Ensure that any doors or vents cannot open accidentally.
Plan for a nearby water source. In a large greenhouse, a water tap should be accessible from the inside. Consider how quickly and easily your plants can be watered in smaller structures. The smaller the greenhouse, the more quickly it will lose precious heat when opened or vented. Plan how to minimize opening and closing the greenhouse to water your plants.
Weatherproofing the Structure
Most greenhouse kits are already designed to withstand outdoor weather conditions. You’ll need to consider your climate before investing in a greenhouse.
If your area is prone to high winds or hurricanes, be sure to choose a structure that can be secured. You might want to consider a polycarbonate material rather than glass as an extra precaution.
Accounting for heavy snowfall is another practical consideration for greenhouse gardening. Choose a structure with a steeply pitched roof so snow can easily melt and slide off. Large snow drifts can block the sunlight from your plants and make the entrance inaccessible. Think about how you will handle snow removal before the first storm hits!
Depending on the size of your greenhouse, you may have room for storing gardening essentials alongside your plants. Make the most of your space by setting up needed supplies within easy reach.
Every greenhouse gardener will need storage for seed flats, pots, soil, and gardening tools. Depending on how many plants you’ll be tending, these materials can take up a lot of space! Regularly inspect your supplies and remove unused items from the greenhouse. The hot, humid environment isn’t ideal for storing seeds, certain tools, or bags of soil. Strike a balance between keeping necessary items close by and using most of your greenhouse space for plants.
Another important element of greenhouse gardening is labeling. You’ll need a system for remembering what plants you’re growing! This is especially true if you use your greenhouse for starting seeds. You can use anything from popsicle sticks to stickers to custom plant markers to label your plants. Just be sure that whatever system you use will withstand direct sunlight and humidity to prevent running or fading ink!
Finally, consider using a calendar or gardening journal to keep track of planting schedules. Since greenhouse gardening allows you to keep growing outside the typical season, you’ll need help keeping track of your planting. Use this space to record your seeds’ expected germination rate, count the days until maturity, and make notes. In many cases, the controlled environment of a greenhouse causes plants to grow more quickly than predicted!
If you’re working with a very small greenhouse gardening setup, choose a spot nearby to store necessary items. Keep everything you need within arms’ reach, or load your supplies into a bucket to carry with you.
The goal is to minimize the time you need to open and close your greenhouse. Letting in drafts will make your greenhouse gardening setup less effective. Whether you keep your supplies in the greenhouse or carry them with you, a successful setup maximizes efficiency.
Controlling the Environment
The goal of greenhouse gardening is to provide plants with a consistent temperature. You’ll need a plan for letting off excess heat. Tender sprouts can suffer from burned leaves and dehydration without venting or cooling a greenhouse as needed.
Some greenhouses have automated solutions for gauging the temperature and venting the roof when needed. Even the simplest temporary cold frames should contain flaps, vents, or windows that can be opened to control the inside temperature.
Whether or not your greenhouse has an automated system, you should always set up a thermometer inside. Monitor the greenhouse frequently to be sure the temperature is within your desired range.
Greenhouses are designed to maximize natural light. However, just as with heat, plants can get too much of a good thing!
Think of how you can provide needed shade for plants that are too tender for full sun. Arranging your plants on shelves is one easy way to do this. Sun-loving plants can be positioned at the top, receiving maximum light from the sides and ceiling. Plants that prefer less direct light and a little shade can go on lower shelves.
Some greenhouse gardeners also install indoor lighting to boost young seedlings. Areas that see a lot of wet, cloudy weather will most likely need supplemental lighting.
Plants in containers often dry out more quickly than those planted in the ground. You’ll need a regular system for watering. This could be anything from a simple watering schedule to an automated sprinkler system.
Many gardeners find that watering their plants from the bottom rather than the top is ideal for greenhouse gardening. This prevents water from evaporating before it reaches the plant’s roots. Periodically set your plant containers in large trays of distilled water. This allows the soil and roots to soak up the water from the bottom of the pot.
You can also set up a drip line or soaker hose to easily water your greenhouse plants when needed. Check out our list of 9 Best Soaker Hoses for Watering Your Garden.
Greenhouse gardening means working with lots of container plants. When plants don’t receive varied nutrition from a garden bed, they need supplemental nutrition. Plan for how you will fertilize and add more nutrients to the soil.
Compost, worm castings, and commercial fertilizers each have their benefits. Using a commercial fertilizer is the easiest way to measure and dispense nutrients to your greenhouse plants. Fertilizer solutions are formulated in specific nitrogen, phosphorous, and potassium ratios. Often called the “NPK ratio,” you can choose the fertilizer with a ratio that best suits your plants’ needs.
Some gardeners prefer homemade fertilizer for economic or ecological reasons. A top dressing of compost or worm casings provides essential nutrients and biodiversity to the soil. While you won’t be able to measure the exact ratio of nutrients your plants receive, both options are quality fertilizers.
Some plants must be hand-pollinated without the help of butterflies, bees, and other garden helpers. This is an especially important element of greenhouse gardening if you are growing berries, fruit trees, or flowering plants.
In a very large greenhouse, your best bet is to use fans or vents to allow a cross breeze. For a smaller setup, hand-pollinating will be more effective.
Some plants, such as squash, pumpkins, cucumbers, and melons, have both male and female flowers. They’ll need help to get pollen from the male flowers onto the female flowers to set fruit. Use a paintbrush or makeup brush to dust the pollen off the male flowers and onto the female flowers. Be sure to use a clean or different brush for each type of plant!
Other fruiting plants have “perfect flowers,” meaning each flower produces pollen and sets fruit. Tapping each flower or holding an electric toothbrush near the stem will help these plants self-pollinate.
Planning Your Crops
Start With Familiar Favorites
When you’re getting your feet wet with greenhouse gardening, starting with plants you’ve grown before makes sense. It will take time to get a feel for how quickly seeds germinate and grow in the new environment. A good way to get started is by overwintering or starting seeds for garden favorites.
As you grow more familiar with greenhouse gardening, you can expand. Try favorite foods that don’t usually grow in your area. You can also grow flowers for a year-round cutting garden.
Grow Extra Plants
If space allows, plant additional seedlings to account for potential losses. Feel free to experiment to find what placement works best for each plant. You can also try different watering systems and fertilizers on two sets of the same plant seedlings. Keep experimenting to find what works best!
Your First Greenhouse Gardening Season
Don’t depend on memory to replicate your results. Keeping a gardening journal to track what worked, what didn’t, and what you’d like to change next season is a good idea.
Your gardening journal is also a good place to note expected germination rates, days to maturity, and other helpful information. Trust us, this is much easier than fumbling through seed packets to try and read the information off the back!
Gardening is a series of experiments. Although greenhouse gardening is based on controlling the plants’ environment, there will always be factors beyond your control. Especially in your first season, try to keep your expenses and expectations reasonable.
Even if your results after the first season aren’t what you hoped, you can apply what you learned next time. As you get more experienced with greenhouse gardening, you can expand and experiment with new ideas!
Ready to Start Greenhouse Gardening?
Now that you know the basics of greenhouse gardening, you’re ready to get started. Year-round gardening is a terrific hobby, whether setting up a small cold frame or a permanent structure. Your greenhouse gardening setup will give you endless opportunities to experiment and refine your techniques.
Don’t be surprised if your greenhouse looks very different from year to year. As with all gardens, there is joy in trying new things.
You can stay on top of your changing greenhouse gardening needs by investing in the right tools. Check out our page on Garden Tools for all the best greenhouse gardening supplies.