For me, the greenhouse has always been the mark of a committed gardener. After all, they're designed to squeeze in more growing time. However, greenhouses often take up a lot of valuable gardening space (and money!). But what if I told you that you could build a greenhouse in your seedbed? With a high-bed greenhouse, you'll get an extended growing season and happier crops, while also saving space! The following content also has some reference value for raised garden beds.
High-bed greenhouses are a great DIY project, but they require some planning. You must assess what your garden needs before you build it (consider location, materials, time, etc.). You will then choose a design based on the many that are best for your particular garden bed. It all seems daunting at first, but we'll cover everything you need to know!
Why use a high-bed greenhouse?
Before we get into the technical details, let's make a raised bed Greenhouse. Flower-bed greenhouses differ from traditional greenhouses in that they are not controlled by temperature or humidity. Instead of being artificially heated, these structures heat the soil by absorbing heat from sunlight. So while the vegetables and flowers inside will be a little roasted, you won't really be able to control the temperature or heat the soil to accommodate plants outside of your garden area. Another key difference is that greenhouses used for seedbeds are smaller and often more portable.
The marginal thermal difference comes in handy at the beginning and end of the growing season, such as when winter begins to set in. More often than not, your garden plants will sense a drop in temperature and end their life cycle (or go dormant). But when we raise the temperature and extend the growing season, we can give our gardens an extra few weeks or even months. This method works especially well with late-harvest produce, such as butternut squash.
In addition to harvesting later in the season, you can also plant earlier (which makes for almost year-round gardening!). This depends on the plant, but many can be planted in the soil 1-2 months in early spring. Frost tolerant plants, such as spinach, are excellent for planting on raised beds in late winter. To determine how early you can start gardening, use a thermometer to observe the temperature in your garden greenhouse and compare it to the planting temperature on the seed packet.
High-bed greenhouses are handy for protecting plants from pests and adverse weather conditions during the spring and summer. They're also great for gently hardening new plants (or just pampering your favorite herbs and vegetables!). In winter, when the ground soil is too cold for planting, a flower bed greenhouse will help protect the roots of temperature-sensitive plants by resting plants on raised flower beds.
Overhead bed greenhouse vs overhead bed spread
If you have a raised garden bed, chances are you've already started using raised bedspreads. Mulch is excellent in gardening, but they don't always feed raised garden beds and soil the way a greenhouse does. The key difference is the material. Raised bedspreads are often made of fabric material with air holes, mesh or even chicken wire, which keeps out pests but does not trap heat. Mulches with solid coverings, such as thick plastic or glass, are technically greenhouses because they keep the soil warm and growable. So, basically, a raised bed greenhouse is a very effective raised bedspread.
Something to think about
A greenhouse is a great addition to raised bed gardening, but it's not a panacea for your garden bed. It has some limitations and minor obstacles that you should be aware of.
The biggest limitation is that a high-bed greenhouse won't grow any of the plants you want. It will only help the soil reach a certain temperature and humidity, depending entirely on where you live. Plants that don't grow on the ground or raised beds in your climate zone won't do much better in a raised bed house (sorry, but dragon fruit is impossible to grow outdoors in the Idaho winter). You need a temperature and humidity control greenhouse system.
Another important factor is that a raised bed greenhouse is completely solid and does not allow much airflow. Even though it's not airtight, you need some real airflow through the system to keep bacteria from growing. You'll also need to turn on the greenhouse during a heat wave to make sure the soil temperature and roots aren't too hot (depending on the weather where you live).
Finally, any greenhouse system creates a barrier between pollinators and plants. If you want to grow fruit, you have to open the high-bed greenhouse when the plants are flowering.
Type of high bed greenhouse
There are many variations of high-bed greenhouse architecture, but most are one of two basic structures: hoop rooms or cold frames. Both plants have their pros and cons, but both are excellent choices for year-round gardening. Plus, there's plenty of room for creativity!
Hoop houses are usually a less expensive temporary option. They have round frames (hoops) that support some type of solid covering -- usually a thick plastic. Hoop houses are quick DIY projects that are easy to build and tear down. Because of this, they are usually only available when needed. Because they were temporary, hoop houses rarely had hinges or easily accessible vents.
Hoop house structures should be made of materials that bend easily. Fine PVC pipe is the most popular choice because of its flexibility and ease of use. You can also use thick wire, hula hoop hut kits, or even hula hoops! The cover also needs to be flexible, as well as clear and durable.
There are several ways to assemble hoop houses on raised beds. The easiest way to do this is to drive the ends of the hoop into the soil and cover it. If your bed is made of wood, you can nail wood hoops to the outside of the bed. Or, for a more permanent solution, you could assemble a hoop house in a raised bed before filling them with soil.
The Cold Frame
Cold frames are fancy high-bed greenhouses that require some carpentry skills (or a large purse). They are mounted on raised beds, often on hinges, making them a permanent part of the garden. The cold frame is used all year round and is easy to open as needed. And, they're usually pretty choices, with a neat box design.
Cold frames usually have a wooden frame lined with high quality plastic or glass. Many are simply repurposed Windows from renovated homes.
Of course, you don't have to plant a bed according to a pre-made greenhouse plan. It's your garden, so feel free to be creative! You can mix ideas together to create your own unique high-bed greenhouse. Alternatively, you can trade in items from a thrift store, such as clean storage containers or empty aquariums.
Some gardeners turn things completely upside down and create raised beds in an existing large greenhouse. This is a great option that saves a lot of space and is easily accessible to vegetable plants. Convex wake-up kits like the Savana Garden bed are the easiest to assemble in a greenhouse, not to mention more uniform.
Build a quick, temporary greenhouse
Time is money (or in our case vegetables), so let's save some by quickly building a greenhouse that's easy to add to a growing bed. This raised bed greenhouse is a simple wooden box frame that can be completed in just a few hours. It's light, so you can add it to or remove it from the raised bed as needed.
The design of this raised bed greenhouse will lie flat on top of the raised bed, so it is only suitable for shorter or immature plants. However, you can easily make it taller by adding legs or using a thicker beam. For a sloping greenhouse where rainwater can run off a raised bed, use thicker beams on one side and cut two vertical beams at angles.
Let's start by gathering some materials. Here's what you need to do:
- 5 boards or stakes (cedar, spruce or any garage free)
- Greenhouse plastic of choice
- Measuring tape
- Wood glue
- Nails (or related fasteners)
- Metal support (optional)
- Staple guns
Now, follow these steps to DIY your raised bed greenhouse:
- Measure the length and width of the convex bed, starting at the periphery.
- Based on these measurements, cut boards to reconstruct the perimeter of the raised bed. Remember to plan in advance how you will join the board. For example, if you create a simple butt, overlapping the board will add a few inches to the length of the second board.
- Cut the fifth plank so that it fits in the center of the frame. If your elevated bed is particularly long, you may need to add two or more of these stabilizers to the bed frame.
- Stick everything together with wood glue. For extra durability, nail the ends as well. You can also install metal brackets on the inside of each corner (cheap shelf brackets are great for this!).
- Set the greenhouse frame aside and pick up your greenhouse plastic. Measure and cut enough material to line the entire frame.
- Use a staple gun to secure the greenhouse plastic to the frame. It should be taut, but not too tight or it will tear.
- All that's left to do is test it! Just place your new greenhouse frame on a raised bed and see how your plants react. You can modify the frame as needed, such as raising it or adding hinges. Now, you have a good system for keeping the soil, plants and roots warm in your raised bed.
Q: Can you put an elevated bed in a greenhouse?
A: Absolutely! Placing raised flower beds in a greenhouse will give you more gardening space, improve drainage and make it easier to access plants than putting them on the ground.
Q: How deep should a greenhouse bed be?
A: If you can only reach the raised bed from one side, make it as deep as you can comfortably reach the soil (usually 2-3 feet). It also depends on the size of the vegetables, herbs or flowers you are growing.
Q: Are raised garden beds warmer?
A: Yes, soil warms because it absorbs sunlight from the sides and from the top (ground soil is only heated from above). However, this also means that raised beds quickly get colder in the winter - hence the greenhouse!