Greenhouses 101: Everything You Need to Know

For many gardeners growing under some kind of cover structure is the only way to get your seeds started early and it's the only way to extend your season as that season comes to a close. So in today's video we're talking with Chris up in Vancouver BC about the right greenhouses or polytunnels for your garden. If you're in the market for a greenhouse or maybe you are just starting to consider upgrading from a temporary hoop tunnel to a more permanent structure like this one then this video is for you. Hey I'm Chris and today I want to help break down some of the terminology when it comes to researching greenhouses and polytunnels because as a shopper once you start researching it can be quite intimidating once you realize all of the options out there. The colors, materials, sizes. Should I go with a kit or should I just DIY the whole thing? But it doesn't need to be overwhelming or daunting. So today we are going to talk about the features of these large structures and then also discuss some differences as well as similarities. So hopefully by the end of the video you'll have a better understanding of what's what in the greenhouse and polytunnel world so that you can make the best decision for your gardening needs. And if you're wondering what the heck a polytunnel is, well it's essentially like a greenhouse but it is constructed differently, it uses different materials, and depending on what you want to use it for it does have slightly different functions. Now with these larger structures there are other options such as geodesic domes or attached greenhouses, so there's like a building and like half of a greenhouse is attached to a building. And there are also all sorts of very creative ways where people can have these enclosed areas for growing in, but for the most part gardeners are looking at either standalone greenhouses or polytunnels to add to their garden. Even though a lot of these structures look somewhat similar, when it comes down to the material they differ quite a bit. So let's just start with greenhouses. When you shop for greenhouses you're likely going to come across this term glazing and all that is referring to is the material that these panels are made from. Now one really popular option still is glass. It is classic, it is beautiful, you can see right through it and with that you get really great light transmission. So the sun comes in, it goes straight to your plants and your plants are happy. Now the thing with glass you have to keep in mind, especially if you grow in a cooler climate, is that it is not very good at insulating. So during the colder temperatures, if you have a heater, that heat will be lost through the glass. So something to keep in mind. Now there is the option to go for the more expensive double paned glass, that is great as well, but the insulation properties are still not as good as some of the other options out there. The other main option you're going to see with greenhouse glazing is this ridged looking polycarbonate. So this is a plastic material, very durable and it is very practical, especially if you have kids or if you're like me, you have trees dropping branches on it all the time. It's durable unlike glass, which I always think in my head is going to shatter if something drops on it. But another reason why I went with polycarbonate for my greenhouse is because of its insulating properties. Now this is a double wall polycarbonate and it insulates really well. I've got a heater and it keeps the inside quite stable, especially during those colder nights. Now you can upgrade to a five wall polycarbonate. It's a little bit more cost upfront, but in the long run I bet you will be saving a lot more money when it comes to heating, especially during those colder winter months. So those are the two main options. They look different, they function slightly differently. Pros and cons. So really it's down to where you're growing and also your choice of aesthetics as well. Polytunnels are completely different because unlike this rigid material that greenhouses are made of, they are covered with this malleable polyethylene plastic sheeting. And if you are going to use this, go for a better quality horticultural grade and a thickness of like six mil. So the better quality, and especially if you can get it like a UV coated one, the longer it's going to last. So with these materials, they are less expensive, but you will need to re-sheet your polytunnel maybe every five to eight years, depending on where you are and if you have a whole bunch of tears that you need to patch up. So with the tears, it's not a big deal. There is special polyethylene patch tape that you can use, but it is something to keep in mind, especially if you live in an area where a lot of branches fall onto your structure or if you are moving a lot of material in and out of the structure, like in a production greenhouse. Now when talking about the differences in the overall look or feel or shape between greenhouses and polytunnels, well, the differences can be quite great, especially if you are doing a greenhouse totally DIY and you are repurposing parts, it's going to look very unique and probably just customized to your space. So that's always really fun to see those creative ideas out there. Whereas for polytunnels, you are likely only going to run into two main shapes. One of the more common shapes is quonset, which is a nice round arch. These structures are quite robust as they're typically made from one long tubing bent to shape. The other common shape is gothic arch, which is somewhat similar, but it has a peaked roof that provides more height down the middle, and also it has a steeper slope which helps shed snow and debris. Regardless of shape, most polytunnels lose some height around the inside perimeter as the poly reaches the ground. So just keep that in mind in case you're thinking of growing taller plants inside. So let's talk about one of the key reasons why gardeners look for greenhouses or polytunnels for their property. Well, it's because we want to control the conditions in here, whether it is for season extension or growing food in ground year round, or like me, I want to do some propagation in a controlled environment. It really doesn't matter what you are looking to do. We're talking about climate control and depending on what structure you go with, the methods and also the equipment involved can vary greatly. So for heating, we briefly touched on that when talking about the glazing types that you can choose for your greenhouse. So a polycarbonate wall, especially like a double or five wall polycarbonate, is going to insulate much better than single or double pane glass. So if you're heating during the winter, you can retain more heat in your structure if you have the plastic material. Now, when we talk about polytunnels, it's slightly different and you may be surprised by this next point. Okay, so it's hard to imagine a single sheet of polyethylene keeping a big polytunnel warm during the cold months. And that's true. With a single sheet, you can't really do much. But with a polytunnel, you have the option to do two layers of polyethylene at the time of installation. And the benefit of that is that you can actually attach a fan to the top of your polytunnel and that blows air to inflate that layer. So you get this giant bubble, essentially like a big bubble-wrapped dome, which is your polytunnel. And that actually provides a ton of insulation, even if it is a large space. So that is one really cool thing about polytunnels that you can't really do with these rigid wall greenhouses. Now, let's talk about the differences when it comes to cooling and ventilating your greenhouse or polytunnel because it is quite different. So in these smaller greenhouses, especially the residential size ones, these rely on passive ventilation. So hot air rises and that's why you get roof vents on these structures and they automatically open with these automatic vent openers. And they are actually quite low-tech. If you look into it, it's pretty cool how the mechanism works, but this is usually what you're going to see in a greenhouse. And of course, if you want more ventilation, you can have a customized, you can have like side panels that open up in the same manner. Of course, you can open the front door and if you can, have a back door as well. And that way you get a lot of fresh air moving through the structure. Polytunnels are slightly different. Unlike greenhouses, polytunnels will not have these roof vents because remember, polytunnels are made from soft plastic sheeting. So unless you're looking at a very large structure where you can add some framing to it and install roof vents, you're likely going to have to rely on the front door and some back opening, whether it's a door or some louvered opening to push air through the structure. Now, what's really cool about polytunnels is that you can have this added side feature to the structure for what's called a side roll-up. So with the poly that drapes on either side, you can have it kind of like free floating and not fully attached to the base of the structure. And that will allow you to attach this long pole with a handle to roll up the plastic so that you can get really great airflow at the bottom. So not only is this great with ventilation, you can actually access the polytunnel from the outside. And this is super helpful if you are actually growing in ground beds or if you have containers along the wall and you want to water them or harvest from them during the main season. It's a really nifty feature that is pretty specific to polytunnels. Before we start talking about similarities, if you were wondering if one costs more than the other, generally greenhouses will cost more based on the materials. So if you're looking for a more economical option, polytunnels are great. Material costs are lower and also the initial setup takes less time, less labor. And also if you inflate those walls, you could be saving a lot of money in the long run in a cooler climate. Chances are whatever you do in a greenhouse, you can do in a polytunnel and vice versa. It really depends on what you want out of the space and what you want to do. So just think of them as very similar structures, even though we talked about a whole bunch of differences. And one of these similarities starts with the foundation. If you're thinking of growing plants in ground, you'll likely have large areas of soil for your growing beds. But if you're looking for a flexible, multi-use space with a potting bench, shelves, and possibly a spot to sit and relax, some popular foundation options are three-quarter crushed gravel, pavers, non-woven fabric over a compacted base, or a combination of all of these materials. So for heating, cooling, and shade, there are a number of similarities regardless of the type of structure that you have. So I've got a little heater here that's plugged into the house. This is 110 volt. If you have a larger structure or you want more heat, you may need the help of an electrician to help up that juice. And when it comes to cooling, we talked about a whole bunch of differences, but at its core, you just want to open windows, open whatever you have so that you can allow for a lot of ventilation to push a lot of the hot air out. And if you want to keep the structure cool, shade cloth works really well. So it's a horticultural fabric, comes in different weaves to allow different percentages of light to come in. So if you want to block out a lot of light, that will help keep the temperatures cooler. Let's not forget to talk about air circulation. So for these large enclosed spaces, we want to make sure that there are no pockets of overly cold, hot, or moist areas, either around plants, under plants, or just tucked away in a corner, because that can lead to all sorts of pests and disease issues, and also general mold and algae issues, which you don't want to deal with in a space that you want to keep clean. So all you need are some small fans for a small space. So I've got two in my greenhouse. If you have a larger space, you may want a couple of those larger ones that you mount onto the roof to really help circulate fresh air throughout the structure. If right now you're thinking, oh my gosh, that's a lot of information. I still don't know if I want a greenhouse, a polytunnel, or something else, or nothing at all. And that's okay. So my tip right now is to sit down, pen and paper, write down some gardening activities that you see yourself doing in a space like this. If you are having a hard time brainstorming some ideas, maybe this is not the right fit for you. Maybe those low temporary hoop tunnels are the perfect fit for what you do in the garden, and there's nothing wrong with that. But for those people who are interested to know more about greenhouses and the whole shopping journey, stay tuned because in the future I am really wanting to do a video on how to help you visualize a greenhouse or polytunnel in your space and how to orient it and really assess your property. So thanks for watching and stay tuned for that next video. I have to confess, I kind of want a greenhouse or a polytunnel now here in the backyard of the Epic Homestead. Hopefully this video was helpful to you. I'm coming really soon. Good luck in the garden and keep on growing.