Sunlight is a key to photosynthesis, the process by which plants produce the food that they need to thrive.  Plants vary greatly in how much sunlight they need.  Some plants require full direct sun, some partial sun, and some shade.  Light requirements will usually be listed on the seed packets or on those little plastic inserts that are typically found in the pots of started plants.  These light requirements will be listed as Full Sun, Partial Sun, Partial Shade or Full Shade. 

            On either end of the sun-shade spectrum, it is easy enough to conclude that a wide open field will have full sun and a heavily wooded area will provide full shade.  You will likely find it much harder to figure out where many other areas of your own garden fall on the sun-shade spectrum.  Typical home gardens are often near buildings, privacy fences, bushes, and trees that can be shading different areas at different times of the day.  The angle and intensity of the sun changes with the season, so the amount of sun a plot receives may also change throughout the growing season.

            First, it’s helpful to know what each sun label on a seed packet or bedding plant actually means. 

            Full Sun:  A plant requiring full sun needs 6 full hours or more of strong direct sunlight each day.

            Partial Sun / Partial Shade:  These two terms are often used interchangeably to mean 2 to 6 hours of direct sun each day, preferably in the morning and early afternoon.  With plants listed as needing partial sun, emphasis is on receiving the minimal sun requirement.  A plant listed as needing partial shade will tend to need to be planted nearer to a shade tree or a building and on the east side away, where it will be sheltered from the hot afternoon sun.  Plants that fall into this category include those that receive filtered sunlight--sunlight that makes its way through a lattice or tree branches.

            Full Shade:  This means little if any direct strong sunlight each day.  Plants labeled as “full shade” require filtered or indirect sunlight.  Full shade does not mean absence of light, just no direct strong sun.  Most shade plants can tolerate a little direct sunlight in early morning or very late afternoon.

            In the past, our only recourse was to observe the light that falls upon a garden site.  It took a lot of dedication to record your garden’s sun pattern at several times of the day and seasons of the year.

            Another issue is that in the spring before the trees are fully covered with leaves, some areas may seem sunny but eventually become shady when their tree canopy has filled in.  You may discover that your sun situation is very different than you thought it was after you keep careful records from year to year and season to season.

            A Better, Easier Method to Measure Sunlight 

            Here’s some good news.  There is a device called Suncalc that will easily provide an accurate measurement of how much sun your plants in containers and gardens are receiving. You can find sources online for under $25.

            I was impressed by my Suncalc.  Using the Suncalc is simple.  Place the sunlight gauge in a flowerpot filled with soil and place the gauge where you want to measure the sunlight.  Press a button to turn on the device and leave the Suncalc in that spot for 12 hours.

            At the end of the 12 hours a flashing light will appear next to one of the following four designations that will indicate that the measured spot was found to be:

• Full sun - 6+ hours of sun
• Partial sun - less than 6 and more than 4 hours of sun
• Partial shade - less than 4 hours and more than 1 1/2 hours of sun
• Full shade - less than 1 1/2 hours of sun

            Stop guessing about your sunlight!  Now you can easily measure it.  For the best success in your garden, keep an eye on the light requirements of your plants and give them what they need.  They will reward you for it.

            For information on a myriad of gardening topics, visit:  www.ohioline.osu.edu and click on “Yard and Garden” link, or call OSU Extension, Butler County at (513) 887-3722, or in Middletown call (513) 424-5351, ext. #3722.

            For up-to-date OSUE, Butler County program information, check out our website at:  www.butler.osu.edu. 

News Release provided by Richard Sunberg.