While this sounds complicated, it is pretty simple to understand the essentials. Contrast of extension is the contrast between two color areas of different sizes.
The primary question that contrast of extension is answering is, “What is the proportion of this color that I need to balance the proportion of that color?”
This is perhaps one of the most important questions in the field of garden color design. An overpowering abundance of yellow in the fall garden is one such problem. We’ve got far too many hot yellow and orange Coreopsis, Heliopsis, Heleniums and Solidago to work with when compared to the other softer colors.
We can balance our colors in a rough way by using the light values (originally designed by Goethe, one of the last truly great Renaissance figures) as follows:
- Yellow = 9
- Orange = 8
- Red = 6
- Violet =3
- Blue = 4
- Green = 6
As an example, the complementary colors of violet to yellow give us a ratio of 9:3 (or 3:1)
Because yellow is so much brighter than violet, we have to use three parts of violet to balance one part of yellow. (you have to reverse the colors to get the right color balance)
In the garden, we might say that we need 3 square feet of violet blooms to balance the color provided by 1 square foot of yellow blooms. Yellow is much brighter and carries more power in the contrast of extension.
Orange, with a value of 8 and blue with a value of 4 is a simple ratio to calculate. At 8:4 (orange:blue) we require twice as much blue to balance an area of orange.
Yellow (9) and red (6) combine at 9:6 or 3:2 so that we require 3 parts of the darker red to balance 2 parts of the brighter yellow.
We always require less of the brighter color to balance the darker color in our garden.
The reality in the garden is that this is never a perfect science. A plant of Coreopsis might be several years older than an Eupatorium or Aster and carry more flowers. Growing a well-designed flower garden is as much an art as it is a science.
We don’t think in terms of individual plants, we think in terms of square footage of blooms or areas of contrast of blooms.
We have to think in terms of wide swaths of color as do painters rather than the individual flowers of gardening imaginations.
I have to point out that the ratios designed only have validity if the flower color contrast of hue are the same. In other words, a bright blue fall aster has to be compared to a bright yellow Helenium and not a much softer yellow Solidago. When a color is paler, it will require a corresponding increase in ratio or area of bloom to balance a more intense color. This then is not an exact science but rather more of a guideline for the gardener. We don’t use our tape measures to evaluate the flower sizes and relative contrasts of extension but we do use our eyes and our judgments. It is this judgment that needs practice over the years to determine a good color proportion.
What About White?
As a last note, white is not mentioned but you can very quickly see that it will have a much higher number than even yellow. This means that a little white goes a very long way in the garden when compared to the rest of the flowers. And I’ll have a post just about white at some future point.
You can read more practical landscaping tips here