Once the peppers and eggplants are in for the fall, garden chores start to ease off, and evenings begin to call for something warm in a mug. Eucommia (Eucommia ulmoides), also known as the hardy rubber tree, contains no caffeine, so a tea simmered from its bark is easy to enjoy after the sun goes down. Snap a piece of the dried bark and you'll see fine white threads stretch across the break, still holding the two halves together. Old medical texts say this thread is how you tell good eucommia from poor.
Eucommia in the Dongui Bogam
The Dongui Bogam (Treasured Mirror of Eastern Medicine), a medical classic compiled in Korea's Joseon kingdom in the early 17th century, lists dujung (杜仲) in its Trees section (木部, mokbu), which gathers medicines taken from trees. Dujung means the bark of the eucommia tree. The text describes its nature as neutral (平) yet warming, its taste as pungent and sweet, and says it is nontoxic. It notes that the bark looks much like magnolia bark (厚朴, another tree bark used in traditional medicine), and it ranks as best the bark that draws out a continuous white thread from inside when you snap it. It also records two other names for it: Saseonmok (思仙木) and Seoksaseon (石思仙).
The text gives preparation instructions, too: shave off the rough outer bark, then slice across the grain so the threads break. The entry's heading carries the mark 【唐】, which shows the herb was imported from China. All of this comes from an old medical text and doesn't reflect present-day medical judgment. Please read it not as a promise of any health benefit, but as a record of how people long ago recognized and prepared eucommia. We've posted the original text with a modern explanation in Homiclub's Dongui Bogam entry on eucommia.
What the White Thread Is, and What's in the Bark and Leaves
So what is the white thread that once marked the best eucommia? It has since been identified as gutta-percha, a natural rubbery substance. Chemical analysis has also confirmed that the tree produces this material and stores it in both its bark and its leaves. In treating the white thread as the telltale sign of eucommia, the old standard and modern analysis agree.
Researchers have repeatedly reported isolating compounds such as chlorogenic acid, aucubin, and geniposidic acid from the bark and leaves. Chlorogenic acid is a polyphenol found widely across the plant world, while aucubin and geniposidic acid are iridoid glycosides. The same studies found that the bark and the leaves differ in makeup. So even when both come from the same tree, a bark tea and a leaf tea will likely hold different compounds.
The old standard and modern analysis also part ways. The Dongui Bogam lists only the bark as a medicine and describes eucommia by its nature and taste. Modern analysis examines the leaves as well and describes eucommia by the compounds it contains. The old idea of a "warming" nature can't be matched point by point against the entries on a chemical profile. And keep in mind that these analyses tell us what's in the plant; they don't tell us what it does in the body when you drink it.
Planting Eucommia at the Edge of Your Garden
Eucommia keeps growing year after year until it becomes a tall tree. Give it a spot along the edge of the garden or by the fence, where it won't cast shade over your vegetable beds. In the Northern Hemisphere, plant saplings in March–April and harvest the leaves in May–July. You can double-check planting and harvest months in Homiclub's eucommia crop guide.
For home gardeners, the leaves are the part worth harvesting. Stripping the bark damages the tree, but you can pick leaves every year without touching the bark at all. When you're choosing a sapling, slowly tear a leaf in half. Gutta-percha builds up in the leaves too, so fine threads will stretch between the two pieces.
Toast and Simmer the Bark, Pan-Fire the Leaves
Dried eucommia bark is sold at herbal medicine shops and tea shops. Start by chopping the bark and toasting it in a dry pan. This breaks up the white threads so the bark simmers more easily, and it brings out a toasty, nutty aroma. Don't let it scorch; toast it only until it darkens slightly. The Dongui Bogam's advice to slice across the grain was meant to break these very same threads.
To brew, add a handful of the toasted bark to 1,500 ml of water and simmer. That makes plenty for one day. A few jujubes (dried red dates) tossed in add a gentle sweetness and make the tea easier to drink, and a couple of slices of ginger added at the end give it a hint of ginger.
In summer, try making leaf tea. Rinse freshly picked leaves, drain them well, then pan-fire them over low heat until dry. Once they're completely dry, store them in an airtight container somewhere cool. It's fun to alternate between the bark tea and the leaf tea and compare their flavors. If you take any medication or are pregnant, talk with your doctor before drinking either one regularly.
This evening, snap a piece of dried eucommia bark, look for the white threads, then toast it and simmer it with a few jujubes.
Source: Dongui Bogam, Tangaek-pyeon (Materia Medica volume), Trees section (木部), "Dujung (杜仲)"
