Host an Event Volunteer Join Tickets

Support the plant database you love!

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.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

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

Search Smarty Plants
See a list of all Smarty Plants questions

Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

Need help with plant identification, visit the plant identification page.

rate this answer
Not Yet Rated

Tuesday - September 29, 2009

From: Phoenix, AZ
Region: Southwest
Topic: Best of Smarty, General Botany
Title: Disappearing sunlight in Phoenix, AZ
Answered by: Barbara Medford


I live in a condo in Phoenix, AZ with a north facing patio that goes out about 10 feet and is 20 feet wide. During the summer months there is a span of 1 foot in the front that goes the 20 foot length where there is full sun. This summer I got some containers and planted blackfoot daisy, bougainvillea, rosemary and some herbs in that patch of full sun. This past week I bought some Fragrant Cloud and Diana, Princess of Wales (re-named Elegant Lady) hybrid tea rose trees to put in this area as well. I got the roses planted in their containers and looked the next day and was surprised to realize there must have been a shift in the tilt of the Earth because I now get NO SUN!!! The shade goes until about 2 feet past my fence into the walkway of the condos. Do you have any suggestions for what I can do with my plants and if they will survive this fall and winter in the full shade? I know UV rays are still outside regardless of if it is shade or full sun, but I am not sure how it works for plants. Any help offered would be extremely appreciated.


Just for openers, we need to tell you that the expertise and research at the Lady Bird Wildflower Center is all about plants native not only to North America but to the area in which they are being grown. Of all the plants you listed, only Melampodium leucanthum (plains blackfoot) is native to North America, and it is not native to Arizona.  But we can tell you from experience and observation that all these plants require full sun (6 or more hours of sun a day) and some can tolerate part sun (2 to 6 hours a day).

You say that your sunlight disappeared, but it didn't do that overnight. And you thought the Earth had tilted, but it is already tilted, at about 23 degrees. Because of this tilt, in the summer the Northern Hemisphere is tilted more toward the sun; the sun rises higher in the sky and is above the horizon longer. In the winter, the Northern Hemisphere is oriented away from the sun; the sun rises lower in the sky, is above the horizon for a shorter period each day, and the sun strikes the ground more obliquely.

If plants have nothing near them, as in a building, and nothing above them, like a tree, they will get whatever sun there is, regardless of the season.  But, visualize your patio: In the summer, the sun is overhead, the building is not casting much shadow, and your strip of sunshine is there. But, now, as winter approaches, the sun is dropped down in the south. When you're facing north, the building is between you and the sun, and you are in the shade, and so are your plants. As you go farther north, this situation is exaggerated beyond what you have in Phoenix; the days are shorter, the nights are longer, and there is less sunlight all around. Plants adapt to this by seeding and dying, if they are annuals, dying to the ground to grow back from the roots when there is more sun if they are perennials, or by becoming semi-dormant, not needing so much sunshine. 

You mentioned UV rays being outside regardless, but that is not how plants use the sunlight. When sunlight strikes a leaf, a process called photosynthesis is put into play, the plant converts the energy from the sun, combines it with water and nutrients in the plant, and metabolizes it into food to support the plant, form new structures within the plant, and store food in the roots. Along the way, it releases oxygen, which is a good thing for the human race. That is a very much simplified explanation, but we wanted to make sure you understood why the plants needed actual sunlight. 

So, to get back to your question. During the period of rapid growth, blooming, setting seed and so forth, those plants will probably have about 4 or 5 months of sunlight during the year. They might even survive with the periods of no sunlight, but they will not flourish. They could be stunted, they probably won't bloom much, and won't be as attractive as you hoped. Phoenix, in Maricopa County, is in USDA Hardiness Zones 9a to 9b, where the average annual minimum temperature is from 20 to 30 deg. F. Probably all those plants will be all right in pots in those temperatures, as it's very doubtful that the temperatures would ever drop low enough for the roots to freeze. Whether you want to continue with those plants out there is up to you, you can't change the amount of sunlight they are going to get. 


More Best of Smarty Questions

How to keep persimmons from staining patio
August 10, 2008 - We have approximately 4 female persimmons bearing fruit around our back patio. Birds are carrying the berries to our patio and eating them which leaves a dark stain on our patio. I'm having to go o...
view the full question and answer

Learning to garden from Hartford CT
May 04, 2014 - Hello, I just recently found an interest in gardening, and have discovered "cultivars." I am having trouble finding what exactly a cultivar is, and if they are bad or not. Can culltivars ever occur ...
view the full question and answer

Gardening advice for Ontario, Canada
April 20, 2011 - HI there. I see most of the readers are in CA, I am in Ontario Canada. I am in need of some advice on a nice flowering all year round garden for both sun/partial sun/shade garden. Some for direct sun ...
view the full question and answer

True date for Earth Day
March 09, 2006 - My grandson asked me to verify the correct date for Earth Day 2006. Sites on the internet say (a) Earth Day USA is April 22, 2006. (b) International Earth Day is M...
view the full question and answer

What is wrong with the bluebonnets?
April 04, 2008 - This doesn't seem to be a very good year for bluebonnets. What's up with that?
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.