In the Northern Hemisphere in September, a small plant spreads low along the ends of garden rows and in the cracks between paving stones. Its heart-shaped leaves grow in sets of three, its yellow flowers open with five petals, and a leaf chewed straight off the stem has a sour tang. You've probably yanked it out and tossed it aside while weeding at least once. This is creeping wood sorrel (Oxalis corniculata), and right now is its fall harvest season.
Wood sorrel is a perennial native to Korea, China, and Japan. It grows best at 15–25°C, grows anywhere between 5 and 35°C, and holds up to cold as well. Give it sun and it will root almost anywhere, from a flower bed to the top layer of soil in a pot. So why grow a plant on purpose when it comes up by itself? Because wood sorrel growing by the roadside may have been exposed to car exhaust or herbicides. For leaves you plan to eat, it's safer to grow your own in clean soil and harvest them there.
Planting: Seeds in Spring, Transplants in Fall
In the Northern Hemisphere, sow seeds in April or May, once daytime temperatures reach about 15°C. The seeds are tiny, so scatter them evenly over the soil and cover them lightly. Any sunny spot will do.
If seeds are hard to find, dig up a plant with its roots from the edge of your garden rows now and move it into a pot. Because it's a perennial, a plant you transplant in fall will leaf out again next spring. Once its seeds ripen, wood sorrel scatters them into the nearby soil, and the next year seedlings come up in unexpected places. That's why it's easier to manage in a pot of its own than in the middle of your garden bed.
Care: Watch When the Leaves Fold
At sunset, wood sorrel folds its three leaflets downward, and in the morning it opens them again. Botanists call this daily leaf movement nyctinasty. If the leaves are folded in the evening, nothing is wrong.
When the soil dries out, though, the leaves stay folded. If the leaves are still folded in the middle of the day, the soil is dry and it's time to water. The plant handles heat and dry ground well, so a thorough soaking after the top layer of soil dries out is all it needs. The Donguibogam (a medical encyclopedia compiled in Korea in the early 17th century) records that this plant grows all over low, damp ground, and you'll still often find it along field edges where the soil stays moist.
Each time you water, check around the pot as well. Seedlings that have spread into neighboring pots pull out easily if you get them before their roots go deep.
Harvesting: Spring and Fall, on Mornings When the Leaves Are Open
In the Northern Hemisphere, harvest from April to June and again in September and October. Pick in the morning, when the leaves are open. The three leaflets stay neatly together then, which makes them easy to prep. The yellow flowers are edible too, so pick some along with the leaves. The leaves are thin and wilt quickly, so pick only what you'll eat and use them the same day.
Before you pick, make sure you don't have clover. Both plants have leaves in sets of three, so they're easy to mix up.
- If the leaves are round with white markings, it's white clover.
- If the leaves are heart-shaped and taste sour when you chew them, it's wood sorrel.
- If it has yellow flowers with five petals, it's wood sorrel.
Eating: What Makes It Sour, and How Much to Eat
The sourness comes from oxalic acid. The genus name Oxalis and the word "oxalic" have the same root. The leaves also contain vitamin C, and studies have found flavonoids in plants of the Oxalis genus.
The Herbs section of the Donguibogam lists this plant as chojangcho (酢漿草) and gives its old Korean name as goeseunga. It describes the plant as cold in nature, sour in taste, and nontoxic. It also mentions that children pick and eat it, and gives another name for it, sanchacho (酸車草). But what old medical texts say doesn't match today's standards. Oxalic acid is also found in leafy greens like spinach, and in the body it can combine with calcium to form crystals that don't dissolve easily. So instead of eating a whole plateful as namul (a side dish of blanched or seasoned greens), use wood sorrel a few leaves at a time, as a garnish. If you've ever had kidney stones, eat even less.
Here are some ways to use the leaves you pick today.
- Scatter a few leaves over a lettuce salad for a sour note without squeezing a lemon. They go limp if they sit in dressing, so add them just before serving.
- Float a few leaves and flowers in a glass of cold water or sparkling water to give it a light sour flavor. Don't leave them in too long.
- Lay fresh leaves over grilled white fish or egg dishes, and their tartness balances the richness. Add them only after the dish is fully cooked so they keep their color and flavor.
Today, look along the edge of your garden for those three heart-shaped leaves and move one plant, with its roots, into a pot. Starting next spring, you can pick leaves for your salads from that pot instead of from the roadside.
Sources: Donguibogam, Herbs section, chojangcho (酢漿草) · Korea National Arboretum, Korean Plant Names Index
