Herbaceous Perennials with Purple Color in Winter

coral bells (Heuchera 'Lime Marmelade')

Winter weather in North Georgia can fluctuate wildly from mild 50+ degrees to downright frigid, below freezing temperatures. We also receive a lot of rainfall from December though February. The changes in temperature, reduced sunshine hours and moisture availability affects the herbaceous perennials that maintain their leaves through the winter months. 

common spiderwort (Tradescantia ohiensis) 

Most herbaceous perennials die back during winter but there are some rebels in our garden that provide touches of color to the otherwise monochromatic landscape. Blushes of purple or red on classically green foliage are indications that these plants are working hard to keep their leaves this time of year. 

golden alexander (Zizia aurea)

We all learned back in school that photosynthesis is light energy that is transformed into chemical energy. The pigment molecules in plant leaves absorb visible light and create the green color we see on leaves during the growing season. The different concentrations of the various pigments dictate the color of green we see [mossy green, lime green, or fern green].

rattlesnake master (Eryngium yuccifolium)

chlorophyll absorbs the light we see as blue and red, and reflects the color green.

As photosynthesis slows, other leaf pigments become apparent. When temperatures drop below 45 degrees, leaves produce more sugar and close their veins to prevent the sugar from moving, producing more intense colors. Under reduced light conditions, [shorter days and often cloudy/rainy days in winter] the color intensity decreases because the plant is limiting the sugars available for anthocyanin production. 

green and gold (Chrysogonum virginianum)

Some plants have naturally occurring purple leaves, thought to protect against sun damage or to hide from insects and herbivores* that are attracted to green foliage. Understory plants often have purple undersides, like the crane fly orchid (Tipularia discolor). In woodland settings the sun's rays are a coveted commodity and plants want to use what they get. The presence of chlorophyll b, which absorbs blue light, helps convert a wider range of the energy from the sun into chemical energy.  

*Fun Fact: plants with high levels of anthocyanin often occur with high concentrations of poisonous phenois, which may indicate that the purple leaves ward off herbivores. 

See my Wildflower Wednesday post for more on Tipularia discolor.

Interestingly, plants that receive too much sunlight can suffer from photoinhibition, preventing the plant to carry out photosynthesis. So when it comes to plants there is a fine balance between too much and too little light. 

Purple leaves are caused by a pigment called anthocyanin, which absorbs green and yellow light, causing them to appear purple. These leaves still contain chlorophyll but the green color is masked by the higher concentration of anthocyanin. 

stokes aster (Stokes laevis)

Even some woody perennials, like the oakleaf hydrangea hang onto their deep purple, fall foliage well into the winter. 

oakleaf hydrangea (hydrangea quercifolia)

Bravo to these perennials that continue to photosynthesis as long as they get enough water; albeit, the process is much slower. They must be looking forward to the warmer months ahead as much as I am when life in the garden gets a little easier.