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Greenhouses are designed to keep the area inside nice and hot so that plants do not die in colder months, but what happens when we are faced with the opposite issue? Greenhouses just get hotter and hotter in the summer unless we make an effort to cool them down.
Your plants certainly won’t be very happy in a boiling hot greenhouse all summer long, that is for sure. We have put together an all there is to know guide to keeping your greenhouse cool and plant friendly through the harsh summer months.
At the end of this article, you should have a vast amount of knowledge on cooling your greenhouse down in the summer. You will also be able to put together a plan of action on how you will be keeping your greenhouse cool using the tips and tricks we have looked at.
Damping down your greenhouse is a very cost-effective way to cool down your plants. All you will need to do is hose down hard surfaces, i.e pathways, and let the water evaporate naturally into the air. The more you can hose down the greenhouse the better. Once in the morning and once midday is enough if you do not have a lot of spare time.
Another great plus to damping down the greenhouse is that the moisture in the air will keep the plants hydrated between watering. It is also a good way of keeping pesky flies and spiders away that will otherwise chomp away at your plants.
Picking the right time of the day to damp down your greenhouse is also very important. If you do it too late in the day, your plants might be already too hot and dehydrated by the time the air moistens or the air might not be hot enough to evaporate the water quickly.
The evaporation process takes some time, so planning when to damp down will make a big difference in the results. Only damp down in the late evening or during the night if it is really hot, or if you don’t have a good ventilation system in place.
The shade will obviously reduce the temperature in your greenhouse, however, be strategic about where you put the shade and how much light you actually block out. Your plants will need light to photosynthesize. It is all well and good shading your greenhouse, but if you don’t allow enough light to come through, you will have another problem on your hands.
Fortunately, there are plenty of special garden shading techniques specifically designed for gardens and greenhouses. Let’s take a closer look at our greenhouse shading options.
See Related Article: Backyard Wooden Greenhouses and Designs
Having external blinds on your greenhouse is much better than internal blinds. This is because it stops the excess heat from getting into the greenhouse in the first place. Whereas internal blinds absorb light when it has already passed the glass and entered the greenhouse, which traps hot air inside.
If you do opt for exterior blinds, make sure they are durable and strong enough to withstand winter winds, as there is no need for you to take the blinds down in the winter. Here are a few things to think about when choosing your internal or external greenhouse blinds.
The color you choose is purely for aesthetic purposes. These days the color makes no difference in how much light and heat are absorbed. Most greenhouses go for green blinds as it is more earthy and suites a garden setting.
Are you mounting the blinds inside or outside the greenhouse? The material you choose for external blinds should be UV protected so that the fabric does not get damaged and wear away. Internal blinds do not require UV protection as the glass absorbs all of the UV radiation.
- Shade Percentage
As we mentioned earlier, you should really think about how much light you want to penetrate the blinds. This will all depend on the plants you have inside the greenhouse.
You may notice some greenhouses are white. They are actually white because of the shade paint used to coat the glass. The idea is to reflect the light off of the greenhouse rather than letting it penetrate the glass and heat up the greenhouse even more.
There are a few different types of paint. Some you can peel off when the summer is over, others you will need to wash off. The quality of the paint is the same, you may prefer to go for the easiest one for you to remove.
The great thing about the paint is once you have applied it, you can leave it on until the end of summer. You also won’t need to fuss about with opening and closing external blinds if you have a very tall greenhouse.
Here is a step by step guide to painting your greenhouse:
- Clean the glass of any dust and dirt.
- Dry the glass.
- Use a radiator roller to coat the glass with paint (you may use a paintbrush if you prefer, however, this will give a streaky appearance).
- One coat is usually enough unless you want the glass to be completely opaque.
- Peel or wash the paint off at the end of the summer.
Top Tip: You can use stencils to decorate the greenhouse when you paint and you want a unique look.
There are a few downsides to using this shading technique:
- Every summer you will have to apply and remove the color at the start and end of summer, which makes the task super time-consuming.
- The paint is very expensive, especially if you are looking to have your greenhouse for a few years.
- You have no control over the heat or light inside the greenhouse once the paint is on the glass. This can result in the plants not receiving enough sunlight on cloudier days.
There is nothing like a good old shade cloth for your greenhouse. Anyone that is looking to save a few bucks will love this shading technique even more. A good quality shading cloth can last for up to 12-13 years. That is a very long time considering most shade clothes cost less than 50 dollars per meter.
Follow these simple steps for installing a shade cloth onto your greenhouse:
- Measure the length and width of your greenhouse as well as ¼ or ⅓ of the way down the sides.
- Have a look at the plants in your greenhouse, how much light do they need? Some plants, like vegetables, need a lot of sunlight per day to grow. In this case, you will only need a shade cloth that shades 30%. You can purchase shade cloths that provide different percentages of shade, so understanding your plants’ needs is important in making the right choice.
- Purchase a shade cloth in the size you measured. You can add a few inches to the length, just in case.
- Place the shade cloth on the greenhouse roof. Make sure the extra bits of material hang evenly on either side.
- Staple the cloth to the greenhouse frame. You will probably need to use a ladder for this. The material must be pulled tight with no dips between the staples.
- Staple all the way around the top of the greenhouse, leaving about 15 inches between each staple.
- Poke a hole on each corner end of the excess hanging cloth. If your greenhouse is large, poke a hole on the rim at every meter of the cloth.
- Tie a thick piece of string through each hole, the string must reach the floor.
- Tie the bottom end of the string to a peg and hammer the pegs into the ground. This will keep the side pieces of cloth in place.
See Related Topic: Greenhouse Kits: Mini, Small, DIY Greenhouses
Shade netting is very similar to shade cloth but the material is much stronger. Shade netting is widely used in areas that experience heavy snow as the netting will take the pressure off the greenhouse and protect it from collapsing under heavyweight.
If you have very heavy winds in your area, shade netting will also reduce the wind impact. This may not make too much of a difference when used for your greenhouse, but who is to say you can’t make a fence out of the netting? Using the netting as a fence around fragile plants that are kept in outdoor gardens will keep them safe and shaded and protected from harmful UV rays.
There are a few ‘catches’ to using this material for shading. The first is that you can only get shade netting in 3 shade percentage options, 50%, 55%, and 85%. That doesn’t give you many options at all. Most greenhouses don’t require that much shade. Secondly, shade netting obstructs vents, something that can be dangerous to the plants.
Follow the instructions for installing a shade cloth if you wish to use a netting cloth on your greenhouse. You can also get blinds made out of shade netting if you want a less permanent structure.
There will be times of the year that you can ventilate your greenhouse without the help of any electrical equipment. These times are usually in late spring and early summer where the breeze is not too cool or too strong and flows through the greenhouse without upsetting the plants.
When the weather is mild and breezy you can simply open the windows and let mother nature cool your greenhouse down. Unfortunately, there will likely only be a handful of weeks of the year that your greenhouse will be able to ventilate from cool outside air, the rest of the time you need to give it a helping hand.
Active cooling is the terminology used for tools that produce enough wind power to cool the greenhouse down. You will need a cooling system that has at least a 3 miles per hour wind speed for the greenhouse to get sufficient airflow.
They are indeed an expensive way of cooling the greenhouse down, after all, they do use up a fair bit of electricity. If you do not already have an electricity source in your greenhouse, the cost of active cooling goes up another notch as you will need to install an electricity source.
So why do people use these tools? On the bright side, using electrical tools such as fans and evaporative coolers will help you control the heat in the greenhouse. Being able to precisely get the temperature to where you want it is a real advantage.
There are so many fans on the market, many of them are very reasonably priced. You should dot a few fans around the greenhouse to make sure there is a good airflow all over. These are great for small or large greenhouses and anyone working in the greenhouse will be just as happy as the plants to have the air flowing.
If you don’t have a lot of space and are wondering where you will cram the fans in, you may want to consider a ceiling fan, rather than one that sits on the ground.
Evaporative coolers are walls that blow moist air around the greenhouse. These are probably the least common active cooling system even though they can bring the greenhouse temperature a whopping 20 degrees Fahrenheit below the outside temperature.
The evaporative coolers use heat to reduce the temperature in the greenhouse by evaporating water. This technique stops your plants from getting overly dehydrated as they are exposed to very damp humid air rather than dry air. To make sure it works effectively the pads should be provided with enough water, the exact amount depends on the size of the greenhouse.
Watering the Plants
Watering your plants may seem straightforward enough. However, watering your plants does require extra care in extreme heat. Here are our top plant watering tips:
- Water the plants in the morning. If extreme heat is predicted for the following day, water the night before, as well as in the morning.
- Check how much water the plant is getting. Do this by measuring how many inches of damp soil surrounds the plant. If the water sits on the top of the soil, your plants are dehydrated. If the water has dampened the soil an inch to two inches deep, the plants have been watered well.
- Water your plants slowly. This ensures the water reaches the plant’s roots and doesn’t evaporate away.
- How does the plant look? Are its leaves wilted? If the plant has seen better days, you have either over watered the plant or not watered it enough.
- If you know that there is a day in the week that you won’t be able to water the plant on time, spray it with antidesiccant. Only do this now and then as a very last resort.
FYI: Antidesiccant is a special spray that keeps the plants moist inside for longer periods of time than water.
What is the Winning Combination?
There are four techniques here that when used together are very successful. These techniques are damp down, cool with fans, water properly, and install a shading cloth. These techniques are not time-consuming at all and once the proper equipment is in place applying the technique is easy.
Follow our perfect guide to a cool greenhouse:
- What plants do you have in your greenhouse? This gives you an indication of the shade cloth percentage to buy. Ask your local garden center for advice if you are unsure what your plants need.
- Prepare your shade cloth to install it before the hot weather kicks in.
- Does your greenhouse have an electrical source? If not you can either install a new electricity source or get an energy charger, whatever works best for you. Large batteries are good for greenhouses that won’t need to be ventilated and fanned for long hours.
- Choose what fans you want to use. Do you want ceiling fans or floor fans? Maybe you want a mixture of both. Think about the spare floor space you have in the greenhouse before making up your mind, the last thing you need is a crumbed greenhouse.
- Think about the watering technique you want to use. Remember, slow irrigation is the most effective way of watering your plants. Once you have chosen the best technique for you, create a watering time table. Check your chores off the list once completed so that you don’t miss anything important out.
- Damp down the greenhouse two or three times every day. This too should be added to the chore checklist.
Those are 6 simple steps to having a cool and thriving greenhouse this summer. You can change the cooling techniques around to suit your greenhouse setup.
Regardless of how you choose to keep your greenhouse cool this summer, make sure you have a good routine and check up on your plants regularly. Most importantly, don’t forget to have lots of fun and enjoy the process.
My name is Isis Loran, creator of the Family Food Garden. I’ve been gardening for over 10 years now and push the limits of our zone 5 climates. I love growing heirlooms & experimenting with hundreds of varieties, season extending, crunchy homesteading and permaculture.