Expanding The Gardeners' Vocabulary

I added a new word to my gardening vocabulary this week: thermotropism. In simple words, this is a plant’s reaction to temperature changes. Rhododendron exhibits one of the most obvious reactions to cold weather. When the weather turns frigid, Rhododendron leaves curl inward. It may look like the plant is suffering from drought, but instead it is reducing the surface area exposed to cold to keep internal moisture from evaporating.

While I was researching thermotropism, I discovered an entire family of -isms in the horticulture world. Phototropism is when a plant moves in reaction to light (sun). I’m sure you have seen in your own gardens how sunflowers turn their heads to the east to catch the morning sun, then slowly turn toward the west as afternoon arrives. Foxgloves and daffodils do the same.

Thigmotropism is when a plant encounters a solid surface and reacts to it – like a morning glory curling around a trellis. A reaction to the presence of chemicals is chemotropism. Think of the way roots move towards areas of higher soil fertility. A plant’s reaction to gravity is called geotropism or gravitropism. Movement in search of water is hydrotropism. And some plants react to touch. The tickle of insect legs will cause a Venus Flytrap to snap closed around its next meal.

The southeast is predicted to experience a serious winter storm later this week, the first measurable snowfall in my town since 2022. It might be an insignificant event in the opinion of my friends that moved from Michigan, Minneapolis, and South Dakota. For this SC native, anything more than an inch of snowfall can rightfully be called a blizzard. So, I’m going to practice thermotropism, and wrap myself into a down duvet like a human taco. Friends, stay safe and warm!

Thirsty? No - COLD! This Rhododendron has curled its leaves as self-protection..

Photo By Nicholas A. Tonelli - Flickr: Nature's Thermometers, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=24186333

Winter Jasmine, The Earliest Flowers

Tubular yellow flowers are erupting on leafless shrubs here in the Carolinas’ piedmont. Winter Jasmine (Jasminum nudiflorum, pronounced JAZ-men-um noo-duh-FLORE-um) blooms early, about the same time as Crocus. The 6-petal unscented flowers are similar in color and shape to Forsythia, but are smaller and fewer. Flowers appear before leaves, and open first at the bottoms of stems, progressing to the tips. The shrub’s weeping structure is similar to Forsythia, but stems are smaller in diameter and young stems have a greenish tint, even when dormant.

Red exterior of unopened Winter Jasmine buds.

Plants reach five feet in height. Like Forsythia, Winter Jasmine will spread aggressively unless controlled. Any stems that touch ground will take root. It flowers best in full sun but will tolerate shade, poor soil, and drought. Left alone, plants take on an unkept, thicket-like appearance after a few years. Remedy this with severe pruning as soon as the flowering season ends. I inherited an overgrown hedge of these plants when we bought a new home. They have encroached into the territory of a nearby row of boxwoods that I want to preserve, so in March I’ll cut the entire hedge to within a few inches of the soil and use a sharp spade to sever and remove the roots outside the target range.

Winter Jasmine stems are squarish in cross section, with four definite angles, while Forsythias are round. Tiny (less than an inch) compound leaves appear opposite on stems, which allows the gardener to distinguish it from Jasminum floridum, a visually similar plant with alternate leaves and the same messy haystack of stems.

Winter Jasmine is an excellent groundcover plant for slopes that would be difficult to mow. Its arching stems look like a waterfall cascading over walls . It is rarely damaged by deer, disease, or insects. It is hardy in zones 6 through 10

A hedge of Winter Jasmine, planted on a steep bank above a business parking lot. Perfect for this location.

The thicket-like growth of Winter Jasmine is evident here. The gray stems are dead and should be pruned out. Live stems are green.

Heavenly Hellebores

Hellebores, or Lenten Roses, are one of the few plants that bloom in winter. They are happiest when planted under deciduous trees, so that they receive full sun in winter (when no leaves are on trees) and are shaded during the heat of summer.

Keys to success:  Don't plant too deeply, or they will die.  Don’t allow mulch or leaves to collect over the crown, or they may rot.  Water them only until established. Wet soil is deadly. No regular irrigation, please.

Hellebores reseed readily, but typically do not come true. What does that mean, exactly? Seeds from a plant with purple blooms may grow into another plant with purple blooms. But it is equally likely that the new plant will have pink or green blooms. I consider this a bonus. (If you come from a software development background, consider this variability an “undocumented feature.”) And they all have different freckles and whiskers that give them individuality.

Use this Thrifty Gardener trick: Put a few plants at the top-most part of a sloping garden bed. Nature and gravity will work together to sow seeds down the slope. In just a few years, you will have a full bed.

To make your plants look their absolute best, keep an eye out for the emergence of new growth. When you see fresh green leaves coming from the crown, grab your pruners and remove all the old, ratty foliage. See the before and after photos, below.