Since I’m gardening on a new plot of land this year, I wanted to know how to best take advantage of the sunlight my site receives. The term ‘sun trap’ kept cropping up, but I couldn’t find a single article that spelled out exactly what it was and how to make one. My permaculture books were also silent on the subject. Naturally, my inner researcher came to life and I scoured forums, videos, and encyclopedias for every scrap of information I could gather—with some extended inquiry into hemispheres, seasons, and the tilt of the earth’s axis. Here are my results.

What is a Sun Trap?

Why Care about Sun Traps?

It’s worth the while of any cold-climate gardener to identify or create warm microclimates on their site. Have you ever longed to grow a certain fruit tree that just can’t tolerate your region’s temperatures? Or maybe you want a longer growing season for annual vegetables without the hassle of starting so many seedlings on your window sills indoors? You might have plants that would thrive better if they didn’t have to suffer that prevailing northwesterly wind. For all these reasons, a sun trap is your friend.

And of course, it isn’t just the plants that benefit. Especially for gardeners who have to twiddle their thumbs through snowy winters, any chance at an earlier spring is glorious. Just imagine watching the first green shoots pop up while the ground elsewhere around them is frozen. Spots like that call me to them every day in early spring, just to look at them and feel hopeful.

Designing a Sun Trap

Picking the Shape and Orientation of Your Sun Trap

The most definitive aspect of a sun trap is its horseshoe shape. Typically the tallest part of the trap is at its centre, and it tapers down in height toward the tips. The area in the middle, surrounded on three sides by this raised structure, has a high degree of wind protection. 

The trap is positioned so that the area inside it experiences as little shade as possible. In the northern hemisphere, that means that the opening will point in a southerly direction. In the southern hemisphere, it will face the north. Site-specific conditions, such as mountain ranges, can affect the exact orientation, but the trap will always point roughly toward the equator.  

It’s tempting for many gardeners to assume that a sun trap should face east, since we think of the sun as coming from that direction. But as the sun crosses the sky into the afternoon, an eastward-facing structure would start to cast a shadow on itself. It’s also important to remember that slopes that face the equator get warm sooner and stay warm longer. This has to do with the tilt of the earth’s axis and the angle of the sun’s rays when they strike the ground. The mathematics are more fiddly than this post needs to unpack (summary: orientation of slope + position of sun = optimal angle for energy absorption), but I’ve observed the effect my whole life: every spring in my Ontario home, the snow on the southern sides of the hills melts well before the snow on the northern sides.

What Can You Use to Make a Sun Trap?

A classic sun trap design is made from living shrubs and trees. Low-growing shrubs are planted at the tips, with slightly taller ones planted next to them and so on toward the tall trees at the back of the horseshoe. The whole planting is tightly spaced, creating a hedge-like effect. The advantage of this strategy is that the trap can be much taller than a built structure, and also integrate valuable trees for fruits, nuts, fibres, and other uses. Trees and shrubs are also great at creating optimal growing environments that have humid, still air aboveground and thriving soil ecosystems belowground.

A popular adaptation of this technique is to combine it with hugelkultur. Classic hugelkultur mounds, built by piling wood and burying it in mulch and soil, are usually straight lines oriented perpendicular to the prevailing wind in order to create a windbreak. However, plenty of growers are experimenting with curved hugelkultur mounds that double as sun traps. The inner side of the mound can be planted as well as the space in the centre of it, creating lots of growing space where happy plants can take advantage of the captured solar energy.

Builders also take advantage of sun traps, especially when they are considering passive solar technology. A deep inner curve in a structure or a freestanding wall can provide a sheltered space for growing plants. It’s also ideal for a cozy outdoor seating area. The effect is enhanced by walls made of stone, cob, brick, and other materials that absorb and hold heat. 

Simple Sun Traps

Of course, all this sounds pretty fancy and work-intensive. But the physics behind a sun trap can be harnessed in all sorts of simple ways: 

• Place a V of plywood behind a single plant. As long as the V is open toward the equator, you are using the fundamentals of a sun trap.
• Grow tall, hardy flowers in a horseshoe shape around smaller, more tender ones. 
• Make a horseshoe of stones in a corner where you want to start your earliest crops. 
• Make a nook surrounded on three sides by barrels of water. The barrels will reflect light onto your plants, and the water will absorb heat
• If you are making terraces, experiment with deep inner curves.
• In spring, note the places on your property where the snow melts first. Consider what plants might thrive there.
• Choose a garden site because two buildings and a line of trees shelter it on three sides. 
• Buy land with a slope that faces the equator. 

Now that you know what a sun trap is, whether human-made or formed by chance, you can take advantage of that knowledge in myriad little and big ways for the rest of your gardening life. I know I will.

Cover photo credit:

Richard Webb CC BY SA 2.0