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Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Tuesday - April 08, 2014

From: Midland, TX
Region: Southwest
Topic: General Botany
Title: How are full sun, part sun, etc, defined?
Answered by: Joe Marcus

QUESTION:

Hello, I have a question about sun requirements. Does saying something needs "full sun" mean a particular number of hours? Does it mean 6 or more hours / day? 8 or more? Is there an agreed upon numeric value for full sun, part sun, and shade? Given that we can fairly accurately model sun conditions now on a site, just curious where the line is drawn. Thanks so much. Love your work.

ANSWER:

There are specific definitions for full sun, part sun, part shade and full shade, but with these definitions there is a healthy dose of art that's thrown in with the science of it.  We define full sun as an area that receives more than six hours of direct sunlight each day.  Part sun is defined as receiving four to six hours of sun each day, while part shade areas get two to four hours of sun daily and full shade areas are defined as receiving fewer than two hours of direct sunlight each day.  However, the mitigating circumstances can be a bit tricky.  For example, afternoon sun tends to be more intense than morning sun.  Sometimes, reflected sunlight can play a significant role in light quality and intensity.  Finally, geography also affects light intensity with desert areas and high-elevation regions having generally more intense sunlight than other places.

 

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