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Permaculture in the Desert: Passive Solar Design and Why it Matters

Use the sun to grow food, heat your home, and save money on your electric bill.

September 27, 2017

Permaculture in the Desert

As a green professional, I have worked on many community projects and private residences. My main goal when working with others to implement permaculture infrastructure, is to teach them the importance and basics of passive solar design. Passive solar design is harvesting the power of the sun during the winter, or rejecting it during the summer, via a building’s windows, walls, and floors to passively heat or cool the home. This happens by collecting, storing, and distributing solar energy (i.e., heat) in the winter and rejecting it in the summer. This is a critical permaculture concept that is important to understand, because it’s at the foundation of the overall design process.

For me, a site’s winter sun patterns are the primary design factor I use to place plants, chicken coops, aquaponics systems, greywater earthworks, and earthworks in general. I want to block the harsh sun in the summer, but harvest it in the winter. The fact that this is not common knowledge speaks to the grip hold that the oil and gas industries have over our society. We no longer have to factor the natural sun patterns into how we build homes, because they are automatically connected to a coal based power grid for heating and cooling. What the sun is doing is irrelevant to contractors building tract homes. This is quite evident in the large suburbs of west Phoenix, where you’ll see two story tract homes that are oriented in such a way that guarantees they will harvest sun in the summer. These homes require more energy to cool and heat. Remember, coal is powering the plant that sends electricity to your home, and it heats up the water for a warm bath. The reality is, we can harness the power of the sun to passively heat our homes in the winter. We can design our property and work with plants to block out the sun in the summer. In this article, I’m going to cover the basics of implementing passive solar design for a home.

Let’s talk about the orientation of your home and why this matters. A home that is oriented on a north-south axis will be harder to passively heat in the winter and cool in the summer. Why? This orientation will receive more sun in the summer and less in the winter. On the other hand, a home oriented on an east-west axis is ideal for passive solar heating and cooling. This orientation will expose the house to more sun in the winter and less in the summer. We want to maintain good southern exposure during the winter to passively heat our home, because it will save us money. I call this the “solar access zone.” We will use less energy and have lower electricity costs with a properly oriented house. A common new gardener mistake is to plant deciduous trees and plants that will block southern exposure. When these plants lose their leaves in the winter, their trunks, and branches will still block the sun from hitting our windows, solar panels, and impact our passive solar gain. Instead of planting deciduous plants we should make use of seasonal trellises to block the harsh summer sun.

Now, let’s talk about basic permaculture passive solar design for growing abundance in the Sonoran Desert. I’m going to focus on the fundamentals and keep it simple. Remember the sun moves throughout the year, so we need to consider these patterns when designing a property. I design for the summer and winter solstice. By placing rainwater harvesting earthworks in the best place, in regard to the sun, we can grow native edible trees that will block the harsh summer sun, yet maintain good southern exposure in the winter.

The winter solstice, when the North Pole is tilted the furthest away from the sun, is the shortest day of the year and takes place between December 20 and December 23. To me, harvesting the winter sun is one of the most critical design factors for a permaculture site. So, how can you harvest the power of the sun? I made an image to visually illustrate a basic permaculture design for a home that is oriented on an east-west access. The first thing I do, is draw a 90 degree angle on the southern corners of the house. Next, I make a 45 degree line to the edge of the property. This is our solar access zone, which is ideal for low evergreens and thick shrubbery. We don’t want tall plants that will block the sun from hitting our windows in the winter. All of our tall growing trees and plants will be placed on what’s called the Master Solar Arc. In my illustration, the Master Solar Arc is made up by tall growing trees that create a half moon around the house. In the summer, these trees will cast major shade onto the house in the morning and evening. On the east, we want to plant deciduous trees. This will allow us to maximize our passive solar gain in the winter by exposing our home to more sun from the east in the morning. On the west, we want to plant evergreen trees. In the winter, shadows cast to the north, which makes the northern part of our properties ideal for stone fruit trees that will be in full shade in the winter as indicated in my illustration.

Now, remember to always plant the rain first. Installing rainwater harvesting earthworks for all of our plantings will give us the most flexibility. We can utilize native plants that thrive on rainwater alone once they’re established. We can grow veggies in earthworks that are able to retain water and save money on our water bill over the growing season. Our earthworks can double as greywater basins and grow stone fruit in our properties’ northern winter shade. By working with the power of rainwater and the sun, we can create a microclimate with rainwater harvesting earthworks growing many multi-layering perennial and annual plants.

Let’s talk a little bit more about water and what we need to think about when starting out. Your water bill is going to explode if you plant mostly non-native plants. This is why I recommend choosing primarily native plants that can thrive on the available on-site rainwater resources. There are many edible, medicinal, and pollinator plants of the Sonoran Desert that would love to live in your yard. Once they become established (which can take up to two years), they are low maintenance, yet produce food and medicine, and bring in pollinators like butterflies and hummingbirds. For fruit trees and vegetable gardens, we need to think about where that extra water is going to come from. Can we install a rainwater harvesting tank to store rainwater for our annual gardens? What about using our laundry machine, bathroom sinks, and the bathtub to irrigate fruit trees? Do not overlook greywater resources. We live in the desert and we can sustain those exotic fruit trees by dealing with our own wastewater onsite. Vegetable gardens need drip or olla irrigation to use water efficiently and grow year-round. Hand watering vegetable gardens, with a garden hose, is the worst for your garden, whether you’re using tap water or rainwater. Hand watering doesn’t allow the water to penetrate deep enough, like drip irrigation, or olla irrigation.

Understanding how the sun works is critical for your growing success. I have been to so many backyards where folks (with good intentions) placed their vegetable gardens or aquaponics system’s in the northern winter shade, and have no idea why they’re not having success growing food. Another common mistake is to plant first and think about the water later. After a couple of years of having plants die in the harsh summer, or tiring from having to water exotic plants daily, people begin to think about drip irrigation. Not necessarily planting the rain, meaning installing rainwater harvesting earthworks that can also double as greywater basins. Drip irrigation by itself is not a replacement, or on par, with similar plants in a rainwater harvesting earthwork. Fruit trees receiving rainwater, greywater, and additional tap water when needed will always be happier than fruit trees on a drip irrigation system. Always think about the water first. Consider the patterns of the sun and the season you’re growing in. This is intelligent design that is based in nature. If you want to learn more, check out the accompanying YouTube video for this article above.

Header image by Jack Dykinga.

Zotero Citlalcoatl is a Permaculture Designer, owner of Camino Verde Permaculture Services and co-owner with Jessica Citlalcoatl of Desert Monsoon Apothecary.  He is also the founder of the “People’s Permaculture Movement” and can be found on YouTube and Instagram. Subscribe to his Patreon, which supports the creation of Sonoran Desert based permaculture media.

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