If you want to have veggies all the year-round and you’re not afraid of a bit of work, growing vegetables in a greenhouse may be just right for you. Managing a greenhouse takes quite a bit of monitoring, and you must be ready and able to provide heating during the cold months (check my reviews of best greenhouse heaters) and shade and ventilation during the warmer months.
It’s also important to understand what plants need to thrive in nature and to replicate those conditions as closely as possible.
In this article, I provide an overview of greenhouse growing along with sound advice to help you succeed. Read on to learn more.
Types of Greenhouses
As you plan your greenhouse, you may be baffled by some of the terminology you come across. For example, it may seem that there are three entirely different types of greenhouse structure or that you need to set up three separate greenhouses. This is not the case, but there are three different ways to keep your greenhouse, depending upon the temperature range you are able to maintain.
1. Cold greenhouse: This type of greenhouse is warmed by the sun’s rays (passive solar energy). It gets as warm as the sun will allow it during the daytime and may drop to around -2 Celsius overnight. This is a good place to over-winter your non-frost-sensitive plants.
2. Cool greenhouse: This type of greenhouse is heated artificially during the winter, but it is not kept “hothouse” warm. You’ll want to maintain a temperature of about 15C during the day and 7C or above overnight. This is a good place to keep established, frost sensitive plants during the winter.
3. Warm greenhouse: This is where you start new seedlings, keep your exotic plants and grow hothouse tomatoes and such. This type of greenhouse stays well heated all winter through. The temperature should not drop below 12-13C overnight and can be quite warm during the day thanks to a combination of artificial heating and passive solar energy.
Heating & Ventilation Pose Challenges
When winter is over, you’ll need to protect your plants from the excessive heat that will surely build up inside your greenhouse. A greenhouse can become very hot (40+ degrees) very quickly if it is kept shut up on a bright, sunny day. This causes some plants (e.g. tomatoes) to stop growing. It can kill others.
To provide good ventilation and cooling, you must have windows and/or vents and fans to bring in fresh air and remove stale air. Provide shade with shade cloths or establish your greenhouse near deciduous trees which leaf out and provide shade during the summer months.
What are the Best Veggies for Greenhouse Growing?
You can grow all your favourite veggies in a greenhouse, but some may be a bit trickier than others. Study the types of vegetables you wish to grow so that you can carefully set up the right balance of sunlight, water and warmth to produce healthy, tasty produce. If you do not provide enough light, or if you try to grow your veggies at the wrong temperature, they may end up flavorless.
Some of the best choices in greenhouse veg include:
When you select your seed, seek out varieties that have been specially developed for greenhouse growth. These perform better than your average garden variety seeds.
Tips for Tomatoes
Most tomatoes do well grown in a warm greenhouse. “Tornado” is a compact variety that does especially well in this environment. The heat and humidity are made to order for them. Just keep in mind that extreme heat prevents tomatoes from bearing fruit. Try to keep the temperature below 32C with good ventilation and shade as needed (you will need a reliable greenhouse thermometer).
If you are keeping a cool greenhouse, try “Alicante”. This variety is especially developed to withstand cooler temperatures.
Grow a Lettuce Patch
All types of lettuces do well in a cool greenhouse setting, but with protection from excessive heat, they can do well in a warm greenhouse. Too much heat results in bitter lettuce. Place your lettuce in an area that receives indirect light and provide shade and ventilation as needed.
Your Cucumber Vine Can Provide Shade
Cucumbers do very well as container plants in a greenhouse. They grow vigorously growing quickly clamber up a trellis. This habit makes them a good space saver and a good companion for shade seeking plants such as lettuce.
Peppers Love the Heat
All kinds of pepper plants do very well in a warm greenhouse setting. Most types are fairly compact and easy to grow in containers. They are fast growing and usually very prolific.
Start Squash Plants
Most types of squash and pumpkins tend to spread out and ramble with wild abandon, so they are not good choices as permanent greenhouse residents. It is a good idea to start your seeds indoors early so that your plants can have the best chance of maturing and producing well in your garden.
Growing Vegetables in a Greenhouse Year Round
With a good greenhouse, you have complete control over the climate, so you can grow your veg all year round. You should harvest frequently because mature vegetable plants tend to be too big for indoor growing. Allocate your space well so that you can have one or two areas in different levels of production at all times.
To plant multiple harvests of plants raised to maturity indoors, carefully study the requirements of each type of plant you want. Choose varieties that have similar requirements and strive to keep your greenhouse at ideal temperature, light and humidity levels for the plants you have chosen.
If you also have an outdoor garden, expand your production by starting seeds indoors in the late winter and transplanting them outdoors after all danger of frost has passed.
What’s the Best Time to Start Seedlings for Transplant?
Use your best judgment and the advice of experienced local gardeners to determine the perfect times for starting your seedlings for outdoor transplant. Every area is different, so it pays to take your time and to befriend members of local garden societies and others who may be able to share a wealth of good information.
If you are starting tomato seeds in a warm greenhouse and plan to transplant them outdoors, generally speaking you should start your seeds early in January. They should be ready to move from small pots to 5 gallon buckets or grow bags by late February or early March.
Once you have transplanted them, place the containers on the south side of your greenhouse for maximum sun exposure. If you use 5 gallon buckets, they can stay indoors if you wish. Otherwise, transplant them to your garden after all danger of frost has passed.
You should see ripe tomatoes by mid June. You can start new tomato seeds in July to have a fresh crop in the winter time.
Start your cucumber and pepper seeds late in February and transplant them into 5 gallon buckets kept on the south side of your greenhouse (or into your garden) in April to harvest late in June.
TIP: At transplanting time, your young plants will need support. Use bamboo stakes, tomato cages or similar structures to provide support. Secure the stems with loosely tied, soft, thick twine or old nylon stockings. A tie that is too thin or too tight will damage delicate stems.
Pollination & Pest Control
Lack of pollinators (bugs, bees and butterflies) in your greenhouse can cause you to have lots of pretty leaves but no fruits and veggies. With no natural pollinators, you will need to perform pollination tasks yourself. Fortunately, this does not involve flitting about from blossom-to-blossom with collected pollen in your cargo pockets.
For most plants, you can spread pollen by shaking the plant gently a couple of times during its flowering time. For tomato plants, tap on their support structures (bamboo stake, tomato cage, etc.) in the morning and in the evening when you see that flowers’ tiny petals have curved back. Your window of opportunity for this is small (3 days) so keep a close eye on your tomato blossoms.
If all this sounds a bit arduous, you’ll be happy to know that you can turn to ladybugs for natural assistance. These jaunty little red and black beetles make a charming addition to your greenhouse, and they are quite efficient as pollinators. In fact, beetles make up the largest group (collectively) of pollinators.
Ladybugs can stay quite happy in your greenhouse garden trundling about from plant to plant drinking nectar and eating pollen. Like most beetles, they are especially fond of blossoms that are green or off white and produce a lot of pollen (e.g. tomato blossoms).
In addition to being good pollinators, ladybugs are also excellent pest controllers. They eat all manner of tiny sap-feeding insects – especially aphids. In fact, a single ladybug can polish off as many as fifty aphids in a day.
Using ladybugs to control pests is a great idea for an indoor, organic garden because they are quite efficient and can keep your garden relatively pest free without the use of any dangerous pesticides. You can purchase young ladybugs from your local garden center or online to release into your indoor garden.
These cute little garden dwellers will live a year or two, and in the course of their lifetime, they will reproduce many times over, so you may only have to buy them once. If you end up with a ladybug population explosion, you can gather up the extras and relocate them to your yard or garden in mild weather, or share them with a fellow gardener.
How to Introduce Ladybugs to Your Indoor Garden
It’s a good idea to release them just before dark and just after you have misted your plants. When you release them, they will be thirsty so they will want to stay on your plants and drink the mist you have provided. As the sun goes down, they’ll settle in for the night. The next morning, they’ll wake up and feel that they are home, so you won’t have any problem with them flying off to seek greener pastures.
TIP: Be careful if you have a pet bird or lizard. Don’t let it roam loose near plants with lady bugs because they are poisonous to birds and reptiles. While wild birds and reptiles are probably wise to this, domesticated creatures might not be.
Is All the Effort Really Worth It?
Maintaining a warm or cool greenhouse can be a bit financially challenging. Heating is not cheap, and if you have a long, cold winter season you may need to seriously weigh the cost of veggies against the cost of heat. Do consider the fact that a greenhouse doesn’t just provide you with fresh veggies, though. It also provides you a pleasant, cozy place to escape and recreate and the opportunity to spend time with fresh, green, living plants in the dead of winter.
Having a steady supply of natural, organic produce is a big plus in today’s world. If your growing season is very short, and/or if you are located in an area where fresh produce is in short supply, a greenhouse can be a source of good food and maybe even a bit of money. If you grow enough produce, you may be able to share it with or sell it to your friends and neighbours.