Ann McCormick, Herb 'n Cowgirl - Writer, Speaker, and Herb Enthusiast

Finding locations with the right sun and shade combination for my plants can seem like black magic. I’ve struggled often with this problem in my years of gardening across three states and in five homes.

The worst time was a yard that had so many trees it felt like I was living in the Forest Primeval. In early spring while the branches were bare, my garden was awash in sunlight, perfect for my sun-loving herbs. Blissfully ignorant of the trouble ahead, I planted basil, dill, and lovage.

But by Memorial Day, the trees had closed in, sabotaging my formerly sunny garden with their green canopy. Soon my herbs were starved for light and began to make desperate attempts to leap across the walkway and find sunnier space.

Why do we so often guess wrong? The answer is in the heavens. Our sun moves, not just during the day but through the year across the face of the sky. These seasonal movements change the amount of light your plants receive. At different times, a garden bed may be shaded by a fence or the neighbor's tree, to say nothing of the irregular shadows cast by the house.

Failing to keep this shifting in mind is responsible for more dead plants than you may realize. Recently I gave someone a Mexican sage bush that needed full sun. He planted it in a section of his yard which he assured me had enough light. But I knew that west-facing wedge was bounded on one side by the house and another by a tall fence. Needless to say, the bush didn’t survive long.

To prevent errors like this, you need to know how much sun your garden gets throughout the growing year before you plant. You can discover this by making shadow maps showing which sections of your garden are shaded during which seasons of the year. Making them is simple. All it takes is a sketch of your garden areas, some colored pens, and a bit of planning with the calendar.

The first thing you’ll need is a map of your property and all your garden spots. Check your records for a surveyor’s map. These are sometimes included in escrow paperwork. If you can’t find yours get some graph paper and make one of your own. You don't need to be exact. An approximation to the nearest foot will do fine.

Once you have the property lines, mark on your map anything taller than you - trees, fences, shrubs, and buildings. Using a regional commercial map find north and mark it on your map. If you have access to weather information, include the prevailing direction of the wind. When you're done creating a master map, make three copies.

Now grab your calendar and mark the weekend closest to June 21, the Summer Solstice. This is when the sun rides highest in the sky, your shadows are at a minimum, and the garden is drenched in light.

Next mark a weekend closest to either March 20, the Spring Equinox, or September 22, the Autumnal Equinox. Either date will do as the sun is in the same position in its travels across the sky. The longer shadows on these shorter days will affect your early spring and late fall planting.

Finally mark a weekend near the Winter Solstice on December 21, when the days will be the shortest and the shadows longest. Mapping shadows on this date is not as critical for most gardeners but if you grow winter crops you’ll find it useful.

For any of the dates, if you can’t do your mapping on the closest weekend, just do it on the next available day. The change in shadows from day to day in the sun’s year-long trek is slow. This is one time when “close enough” really is good enough.

On the days you’ve marked, go outside and sketch the edges of the shadows at 10:00 AM, noon, and 2:00 PM. Use a different colored pen or a symbol to tell the edges of the shadows apart on your map. Label your sketch with the time of year it was made.

When you’ve finished making your maps I guarantee you’ll be surprised. Those shadows reach farther into more places than you think.

You now have crucial information needed to help you know where to plant your flowers, vegetables, and herbs for just the right amount of sunlight. Sections of your garden in shade on the 10:00 AM and noon maps but in sun by 2:00 PM can be considered “afternoon sun.” Parts that never see a shadow are full sun and should be host to your most drought tolerant plants.

It takes a little planning, but you’ll reap benefits for years to come by creating a shadow map of your home gardens. Your shade loving ferns and your sun loving herbs can now happily grow in the spots best for them.

Sidebar: The Science of Shadows
The length and direction of shadows in your back yard is the product of three factors – your latitude or distance from the equator, the tilt of the earth’s axis, and the earth’s orbit around the sun. In our part of the globe the sun is lowest in the sky on December 21 (Winter Solstice) and highest on June 21 (Summer Solstice).

How much of a difference is there from place to place? Well, for Houston the sun is 36 degrees above the horizon at the Winter Solstice and 82 degrees at the Summer Solstice. Move up to Amarillo and its only 30 degrees at the Winter Solstice and 74 degrees at the Summer Solstice. That makes a big difference in the total light and length of shadows.

Mapping Shadows For Good Gardening