Discussion of Colors, Forms or Varieties forum: Color as are faded?

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Stacilacee
Aug 16, 2020 8:39 PM CST
This is my first year growing dahlias and needed some help from experienced growers. I live in zone 9a so we are dealing with warm weather. I’ve placed shade over my garden beds to help but notice some of my varieties colors seem faded compared to what they should be. Any suggestions on what I can do?
Thank you in advance!😊 Staci
Imageteddahlia
Aug 17, 2020 4:02 AM CST
Name: Ted
Oregon
We enjoy breeding new dahlias!
Shade cloth is wonderful in warm climates but there are some varieties that need sun on the opening buds to form red pigment. It looks like fading but the red pigment did not develop. In the old days , people would use umbrellas to shade dahlias but they found out they needed to allow the sun to hit the buds and when they were about half open use the umbrella to keep the sun from fading the bloom. .
We like to place a sign on our porch that says: We are in the garden. Really, we are always in the garden.
SteveM
Aug 17, 2020 12:41 PM CST
Name: Steve
San Diego
Commercial cut flower grower
I use 30-40% shade cloth and notice that all of my colors fade less under the shade cloth than if the same varieties are grown in full sun. So, (just a theory, no proof) the lack of pigment expression Ted refers to must occur at a higher percent blockage of the UV rays than 30-40% (e.g., an umbrella).

At certain times I will have a variety fade no matter if it is in the sun or under the shade cloth. I don't know why but suspect it might have something to do with higher humidity or a temporary imbalance of nutrients or...

[Last edited Aug 17, 2020 12:42 PM CST]
Quote | Post #1353564 (3)
Imageteddahlia
Aug 17, 2020 1:03 PM CST
Name: Ted
Oregon
We enjoy breeding new dahlias!
My information came from the Stanford website where Dr Walbot had students do short scientific experiments on dahlias. The buds of the flowers were covered in aluminum foil and the color compared to those that were grown uncovered. Some anthocyanins require sunlight to form .. This is also evident in black foliage plants where the anthocyanin in the stems and leaves is darker in full sun.

In my garden I have a variety called Hollyhill Fireball that requires sunlight to form the red flame flowers. It needs the sun so bad that in the course of the season the flowers become lighter in color going from an intense flame to a lighter flame and ending up almost solid yellow. It is the shorter hours of sunlight that cause the change in color. It is my theory that not all anthocyanins take the same amount of sunlight to form. There are several versions of anthocynins in dahlias. So, if your variety is dependent on sunlight to form pigment the flowers will be much lighter under shade cloth. Yellows need no worry. Whites my look good there. Some reds will be OK. Others will not do well. What about purple? I do not use shade cloth and do not know.
Shade cloth cause overly tall plants and long stems in our area. 11 foot tall plants are commonplace. Stems can become too long to show. Umbrellas can be folded up easily and extended easily for the best of both worlds.
We like to place a sign on our porch that says: We are in the garden. Really, we are always in the garden.
SteveM
Aug 17, 2020 2:10 PM CST
Name: Steve
San Diego
Commercial cut flower grower
I agree, dahlias need a certain amount of sunlight in order for the pigments to express. But, 30-40% shade seems sufficient (here) for full anthocyanin expression while, at the same time, keeping the reds and dark reds from fading. I also get a better blush on the whites under shade compared to full sun (when the lavender washes out). Likely, somewhere on the scale there is a point where too much sun blockage will restrict antho expression. Is it 50%, 70%, 90% shade? I don't know if anyone has done a study to find out. Maybe a good experiment for Staci. Smiling

As far as plants 'stretching' under shade cloth, I do get a height increase of about a foot on varieties grown under shade cloth. Since I am after long stem this is actually a desirable trait. Dahlias grown further north would likely stretch more, considering the longer day length.
Stacilacee
Aug 18, 2020 11:10 PM CST
Thank you so much for all your help!

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