Sustainability Series: Saving Water in Your Greenhouse

Gardening in your greenhouse can bring about a multitude of benefits from the ability to create a unique microclimate and grow tropical plants in snowy conditions to simply keeping exterior threats away from your plants. Greenhouses are a modern marvel of underdiscussed technology, in my humble opinion, as they have slowly become integral parts of food supply chains both local and global. However, one drawback to greenhouses is that you are cutting your plants off from the natural world, so you must supply the water. Depending on the size of your greenhouse, you could be using a lot of water just to keep your plants comfortable. Even here in the Pacific Northwest we are not immune to the effects of drought, despite the prevalence of cloudy days. Being smart with your usage of water is not only good for you and your plants but for the planet and everyone on it as well. Luckily, it’s not hard to reduce your water waste while keeping your plants happy and healthy. Some methods may be easier than others, but that’s more or less true for everything. Just remember that its for a good cause, life in all forms require water. We as humans, at least speaking for myself, prefer to drink clean water if and when I can. So, that being the case, why not try and waste as little clean water as we can to ensure we can have enough moving forward. That will end the preachy portion of this blog, going forward I will present to you some techniques that can potentially help you save water in your greenhouse!

There is an old technique in greenhouse gardening in which water is sprayed upon the flooring medium where it is left to evaporate and distribute moisture into the warm air and cool down the temperature while providing water to the plants. Now, I don’t wish to mock this method, it’s tried and true for a reason. But that doesn’t mean it can’t be improved upon! First things first, you should address your flooring medium. Concrete slabs may be the most attractive option for multi-purpose, durable greenhouse flooring, but they aren’t great for saving water. To maximize water saving using this method you need a flooring medium that will store water to be distributed throughout the day. Wood chip mulch is a good option as it can be naturally sourced from tree felling, just make sure you plant some more! Mulch, however, does need to be replaced. Lightly used greenhouse mulch, one to two seasons, can probably stand to be replaced around once a year. More frequently used greenhouses, three to four seasons, should be replaced around twice a year. Over time mulch starts to lose its ability to retain water over time resulting in you having to water your greenhouse more frequently. You can tell when mulch needs to be replaced as it begins to lose its color. Unfortunately, mulch being a natural substance, can breed mold and rot. Proper air circulation is a good way to avoid this, but its not a perfect cure all. Lava rocks are great flooring medium in terms of retaining water and releasing it over time as well as their longevity. Lava rocks don’t need to be replaced as often as mulch, but they also won’t last forever. You should be diligent about keeping them clean, but overtime they will degrade. The constant walking upon and water being sprayed will eventually degrade your precious rocks. Pea rocks and broken up shale are less expensive initially than lava rocks but will likely only last half as long. Don’t get me wrong, they’re great flooring mediums, but they are a tier below lava rocks. Once you’ve decided upon your flooring medium of choice, you can try and play some games with the humidity and water amounts. Increasing the amount of air circulation and ventilation will help distribute the moisture you spray onto your flooring medium. This will ensure you don’t need to spray as much water so long as the temperatures are hot enough to evaporate the moisture. Over spraying water can harm the process of evaporation as it begins to pool up and the energy required to heat up water molecules increases proportionally to the amount of water. Basically, the larger the puddle, the hotter it has to be in the greenhouse to evaporate it.

Another option to save on water is to install an automatic misting system. These systems are wired to release specific amounts of water in the form of mist over periods of time. They should be installed high up in your greenhouse to maximize you water usage. The water being released as mist allows for less heat energy to be spent on evaporating what water does accumulate through out the greenhouse. The less heat lost to evaporation; the less heat that needs to be added to the greenhouse system in the colder months. Humidistats can also be integrated into these systems as they inform the misting system of the relative humidity inside the greenhouse. Humidity is very important inside a greenhouse but can become detrimental if it gets out of control. Misting the greenhouse is the best way to drop the temperature inside a greenhouse so if things get too hot, the misting system will kick in. Your air circulation systems should help keep the humidity down to normal levels, but it never hurts to have a failsafe.

If rainwater is plentiful during certain periods of the year as it is near me, collecting it is a great way to supplement your water usage during the dry months! Rainwater barrels are a great way to collect the rain when its around and store it for when it isn’t. You can maximize your rainwater collection by installing collection barrels on your home as well as on your greenhouse. Make sure you have filtering systems for your rain barrels either on the collection end or once you decide to use it. Keeping water is a great idea, but if it’s not clean, you might have a mess on your hands. Stagnant water tends to breed some nasty stuff, but you can combat this via filtering systems or water purification chemicals. There are studies that suggest you can use UV light to clean out water from nasty parasites and if you have a greenhouse, you probably have some UV lamps hanging around. No pun intended. You may be thinking, ‘But I live in an area where it rains all the time, when would I need to use collected rainwater?’. Well, living north of the Seattle area, I am essentially in a rainforest. However, during summer months, lawns turn brown, and towns have watering restrictions. Water shortages are a very real thing and having clean, useful water around is never going to be a bad thing. Stored water can also be used for other situations or emergencies if you need it.

Updating your equipment is also a great way to ensure you aren’t wasting water. Leaks and drips are terrible ways to waste water and are far too frequent in gardening setups. Spray nozzles can be water wasters as well if their spray is less than accurate. If you are spraying your garden yourself, you would be the first to notice if you’re spraying everything but the plants. This can be a big waste of water but can also be dangerous if you get the foliage too wet. Wet leaves breed mold and disease. It’s more physically demanding but misting your garden yourself can help control exactly how much water you use and where. Automated systems will likely be better at gauging how much water is used as you can set a watering limit, but you certainly have more control over where the water is being sprayed. You can also use a watering can if you want to go old school. This is by far the most physically demanding method I’ve suggested, but it is a great way to measure exactly how much water you are using and where its going.

You can always pick and choose which method or combination works best for you. Watering cans can be a good way to transfer the water you’ve collected in the rain barrels to your plants. You can also use the rain barrels to be the source for your automated misting system. It’s all about personal preference, so long as you are actively taking steps to conserve water that’s all that matters.

I really do appreciate all of you that have read through this blog post. This is the first of many upcoming sustainability based blog posts. I think anyone who owns a greenhouse is already interested in sustainability, actively or not. This blog series is especially close my heart. Some of my most precious memories involve being outside, hiking around the woods or hanging around on mountains skiing, hiking or camping. I studied Business and Sustainability while in college so being able to work in my interests into this job is really an awesome thing. I am always striving to make the world a better place, if I can inspire even just one person to be more conscious with their water usage in their greenhouse after this blog post than I’ve been successful in my mind. Small steps made by individuals may not seem like much on the surface, but all together our actions can lead to something much bigger, something greater than the sum of its parts. We are all on this earth together and we should all play a role in keeping it habitable. Once again, thank you all. Until next week.