I’ve been wondering lately if a greenhouse should be in full sun. I mean, a greenhouse’s job is to harness heat, right? I live in a warm area, though, so I was wondering if full sun is too much sun.
Should Greenhouse Be in Full Sun? Yes, a greenhouse should be in full sun. While there may be times of the year you have to manage the sun; it’s better to have as much sunlight as possible rather than too little. There are plenty of options to minimize the full sun in warmer summer months.
Now you know sun is very important for your greenhouse, but why is it so important? I did some research that helps explain why that bright, sunshiny sun is vital to your plants’ health and to give you some idea how to minimize it when needed.
Sun is Vital to Your Plant’s Health
A plant cannot grow without sun; there are no two ways about it. Without sun, your seeds would never even sprout from the soil let alone grow and produce.
Plants grow through a process called photosynthesis. You might remember the term photosynthesis from junior high science. You might even have done an experiment like I did where I grew one plant in sunlight and another in a cupboard for artificial shade.
Even if you didn’t do the experiment, you probably know as well as I do, that the plant in the sun thrived compared to the one in the cupboard.
Take a quick look at the process of photosynthesis.
- Plants take in sunlight
- Plants use the energy from the sunlight to convert water and carbon dioxide into glucose or sugar
- Plants use glucose to make cellulose and starch
Cellulose builds cell walls within the plant and starch is stored in seeds as a food source for the plant. Without this, the plant can’t grow. So, as you can see, sun makes the world go round for a gardener.
The more light absorbed, the more energy provided for photosynthesis. A higher level of photosynthesis means more sugars are formed and you see more growth. You’ll find bigger flowers and more productive crops all throughout your greenhouse. Who wouldn’t want that?
A greenhouse allows you to harness the energy from the sun at an even higher level. Greenhouses are usually made from glass or clear plastic. This allows the maximum amount of sunlight to enter the greenhouse.
The sun comes in and turns to heat when it hits the ground or plants inside your greenhouse. Since a greenhouse is generally sealed off, the heat hangs around and warms up the air. This is especially helpful in cooler months.
Positioning Your Greenhouse to Maximize Sunlight
Since we know how important full sun is to a greenhouse and how sunlight helps plants grow, it’s important that you position your greenhouse so it receives the maximum amount of sunlight.
The best location for your greenhouse to get full sun is south or southeast of any structures on your property. If this isn’t possible, a spot east of any structures is the next best option.
As far as which direction your greenhouse should be oriented for maximum sun exposure, it depends on the state where you live. Take a look at this table.
|Orient East to West||Orient North to South|
If your state appears in both categories, then the orientation of your greenhouse depends on where you live in the state and your hardiness zone. Your best bet is to check a zone map with the U.S. Department of Agriculture
If you’re in zones 6 and below, you should orient your greenhouse east to west. All other zones should orient it north to south.
Once you find the area that gets the most sunlight, look for a level area and lay a layer of landscape cloth. This helps keep weeds out but still allows for adequate drainage.
Here are some other things to keep in mind when it comes to the location of your greenhouse.
- Convenience: If you’re like me, you’re much more likely to spend time out in the greenhouse if you don’t have to trek clear across the yard.
- Access to electricity: Electricity is critical in warmer months for fans or a mechanical ventilation system. In winter months, you’ll need it if you have to supply artificial heat.
- Access to water: This one’s pretty obvious – you don’t want to be running back and forth with buckets of water when it comes time to water your plants. It’s also useful to have it near in the summer if you want to fill big buckets to bring down the temperature in your greenhouse.
- Avoid trees: As these trees grow, they may begin to block the sun from hitting the greenhouse.
Also, keep in mind; plants actually do need darkness for some amount of time. When it’s dark, plants break down the energy created through photosynthesis for growth. This is called respiration.
Managing Sunlight in the Warmer Months
Depending on where you live, there may come a time when you need to manage the amount of sunlight your plants get. Interestingly, it’s not actually the light that’s the problem, but the heat energy from the sun.
Photosynthesis will actually stop if the environmental and plant temperature gets high enough that the plant has to use all it’s water to cool itself down.
You can manage the amount of full sun entering your greenhouse a number of different ways.
- Shade cloth
- Planting deciduous trees
- Strategically placing your plants
Ventilation: Having a good ventilation system installed in your greenhouse can help cool things down in the warmer months.
Greenhouses use either a natural or mechanical ventilation system. A natural system uses vents to circulate air while a mechanical system uses fans or other devices for air circulation.
Shade cloth: Shade cloth is a very effective way to cut down on the amount of sun entering your greenhouse. You can put shade cloth over the top of the greenhouse, on the interior roof or even just a few feet above plants.
Shade cloth comes in varying densities, ranging from 5 to 95-percent. The density shade cloth you use depends on what you’re growing. Take a look at this table.
|50% Shade Cloth Density||75% Shade Cloth Density|
|CabbagePeppersLettuceSome OrchidsPot plantsGeraniumsCaladiumsIrises||OrchidsSome FernsLarge olive trees|
Here’s shade cloth I found on Amazon with a density rating of 50 to 60-percent.
Planting deciduous trees: Planting deciduous trees on the west side of your greenhouse can help provide shade during the spring and summer seasons. Once the tree’s leaves fall off in autumn, it allows sunlight to reach the greenhouse again.
Just to clarify, deciduous trees are any trees whose leaves fall off every autumn. Here are some examples.
These trees may start off small but will grow quite large and provide a nice covering for your greenhouse during the hottest months.
Strategically placing your plants: When you plan out your greenhouse, thinking about where to place specific plants also helps with sun exposure.
For example, placing large leaved plants along the wall of your greenhouse as well as in areas that get more sun can save smaller plants from the extra sun exposure. Some good choices might be fig trees, grapevines or rhododendrons.
You can also consider which plants need more sun and which are pretty tolerant to shade. Take a look at the table for examples.
|Shade Tolerant||Medium Sun||Full Sun|
What Happens When a Greenhouse is in the Shade
Plants that get too much shade will usually try to make up for their lack of sun. They do this by stretching to try to get more sun. This means their stem will grow taller, but their roots will be weak and their leaves small.
If this has already happened to you, all is not lost. A plant that grows like this in the shade will never fully recover, but can still become healthy and produce fruit.
Here’s a look at how the different environments are broken down.
|Full sun||6 or more hours direct sunlight|
|Partial sun||Between 4 and 6 hours of sun|
|Partial shade||2 to 4 hours of sun|
|Shade||Less than 2 hours of sun|
If you end up putting your greenhouse in a spot that gets too much shade, there are ways to help make it a bit better.
- Trim trees
- Grow lights
- Check spacing
- Change up your plants
Trim trees: Look around the outside of your greenhouse to see if there are any trees casting shade over your greenhouse. If there are, see about trimming back the branches to allow more sunlight.
Grow lights: Grow lights are a useful way to provide the necessary light and heat for good plant growth in your greenhouse. They come in a number of different types.
|Type of Grow Light||Characteristics||Lifespan||Placement|
|Incandescent||Least expensiveNot very efficientHigh heat output||700 hours||24 inches above plants|
|Fluorescent||Low heat outputReasonable range of light||10,000 hours||12 inches above plants|
|LED||Very energy efficientSuper low heat outputIdeal range of light||50,000 hours||6 inches above plants|
You’ll have to adjust the placement of your grow lights as your plants grow to keep them a reasonable distance from the plants.
Check spacing: Don’t just think about the overall shade in your greenhouse. Think about each individual plant.
You may start seedlings with appropriate spacing, but as plants grow, leaves from other plants may overlap and prevent the sun from reaching smaller plants. You’ll end up with smaller fruit because of this.
Change up your plants: Too much shade doesn’t have to be the end of your greenhouse adventures. There are plenty of plants that do well in partial or full shade. It might just be time to redesign your greenhouse with a few of those plants.
Here’s a look at plants that embrace a shady environment.
- Impatiens (One of the only plants that still offer beautiful flowers even in the shade)
- Oakleaf Hydrangeas
So, it’s best to place your greenhouse in full sun. Remember, we’ve shown you a number of different ways to manage too much sun during the warm, summer months.
Recreating the perfect growing environment without sunlight is a bit more challenging.