Ornamental · Rubiaceae
Sweet Woodruff
Galium odoratum
A fragrant shade carpet that all but grows itself once the soil stays cool and moist.
Full shade
Every 3–7 days
USDA 4–8
6–12 in · 15–30 cm
Overview
Sweet woodruff is a low groundcover that thrives in the cool shade where little else fills in. It belongs to the Rubiaceae family and carries its narrow leaves in tidy whorls around square stems, topped by small white star-shaped flowers in late spring. Crush or dry the foliage and it gives off a sweet scent of fresh-cut hay, the trait that earned it a place in old herb gardens.
Give it the dappled shade under trees or the north side of a wall and it knits into a dense, even mat in a season. It spreads by creeping rhizomes and self-seeding, fast enough to cover ground and fast enough to wander, so it shines as a groundcover but wants edging or a barrier where beds are tight. In hot, dry sun it scorches and may go quiet for the summer.
It is one of the easier plants to keep, with no serious pests or diseases when sited well in the cool, moist, humus-rich soil it favors. The catch is the coumarin in its leaves, the very compound behind the scent. A small amount flavors the traditional German May wine, but large quantities are not safe to eat.
Care
The short version: cool, moist, humus-rich shade and a slightly acidic soil. Water through dry spells, feed almost never, and give it edging if you don't want it to roam.
Light
Plant it in full to partial shade, the kind of dappled light found under trees. It will take a little morning sun, but hot, dry, full sun scorches the leaves and pushes it into early dormancy.
Water
Keep the soil cool and evenly moist, watering roughly every 3 to 7 days in dry weather. It tolerates dry shade once it's settled in, though it stays greenest where the ground never fully bakes.
Soil
It wants humus-rich, well-drained loam on the acidic side, with a pH of about 5.0 to 6.5. Work in leaf mold or compost and it spreads happily.
Temperature
Hardy and tough, it survives down to about -29°F (-34°C) and grows well up to roughly 84°F (29°C). Past that, in dry heat, it scorches and may rest until cooler weather returns.
Humidity
Ordinary outdoor humidity suits it, so there's no number to chase. In dense, stagnant plantings, good airflow matters more than the moisture in the air, since still, humid pockets invite the odd leaf spot.
Feeding
This is a light feeder that rarely needs much. A thin spring topdressing of compost or leaf mold is plenty, and overfeeding only pushes the spread you're already trying to manage.
Pruning
Pruning is minimal. After bloom, shear or mow back any tattered or scorched foliage to freshen the mat, and the same cut helps hold its spread in check.
Repotting
Grown in a container, it needs dividing and repotting every 1 to 2 years as the rhizome mat fills the pot. Crowded roots, a tired center, or a mat outgrowing its space are the signs it's time.
Size & spacing
It stays low at 6 to 12 inches (15 to 30 cm) tall while running wide. Each plant spreads 12 to 24 inches (30 to 60 cm), so set them about that far apart and let them close the gaps.
When to plant
Sweet woodruff follows the cool seasons. Start seed in late winter to early spring after a cold spell, set divisions out in spring or early fall while the soil stays moist, and look for the white flowers in late spring.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Late winter to early spring; seed germinates slowly and benefits from cold stratification
- Plant: Spring or early fall in shade
- Harvest: White star-shaped flowers in late spring (April to May)
Hardiness
USDA hardiness zones: 4–8
Temperature: down to -34°C
Troubleshooting
Sweet woodruff has few real troubles, and the ones it does have come down to siting. Watch the margins for spread and the leaves for scorch in too much sun. Match what you see below and adjust before it gets away from you.
Spreading well past where you planted it
Sweet woodruff travels by creeping rhizomes and self-seeding, and in the cool, moist shade it loves it can run straight into neighboring beds. Sink a root barrier or some edging before it gets going, and lift unwanted runners whole by loosening the soil rather than pulling at the brittle stems. Shearing after bloom keeps it from seeding even further.
Fix:
- Install a physical root barrier or plant in a contained bed or sunken edging
- Dig out unwanted rhizomes by loosening the soil and lifting them whole rather than pulling stems, which break easily
- Deadhead or shear after flowering to limit self-seeding
Browning, scorched leaves and a thinning patch
Leaf scorch shows up when the plant sits in hot, dry, sunny ground instead of the cool shade it wants, and in a bad spell it simply goes semi-dormant for the summer. Move it into part to full shade, mulch to hold the soil cool, and water through dry stretches. Cut the burnt foliage back and fresh growth returns once the weather eases.
Fix:
- Move or establish plants in part to full shade
- Keep soil cool and evenly moist with mulch and supplemental water in dry spells
- Cut back scorched foliage to encourage fresh regrowth once conditions cool
Spotted leaves in a crowded, airless patch
Now and then a fungal leaf spot turns up where the air sits still and the foliage stays damp. Thin out the crowded growth so air can move through, water at the base instead of over the top, and clear away the marked leaves. Sited well, sweet woodruff has no serious pests or diseases to speak of.
Fix:
- Improve air circulation by thinning crowded growth
- Avoid overhead watering and water at soil level
- Remove and discard affected foliage
Toxicity
Sweet woodruff is mild rather than dangerous, but it isn't a free-for-all. The leaves hold coumarin, the compound behind their sweet scent, which is fine in the small amounts used to flavor May wine. Eaten in quantity it can thin the blood, strain the liver, and bring on dizziness, so keep large helpings away from pets, livestock, and people alike.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Caution
A nibble of the foliage is unlikely to do much, but the coumarin it carries makes a large helping a poor idea. Watch for an upset stomach or sluggishness if a cat eats more than a leaf or two.
Dogs Caution
Small mouthfuls tend to pass without trouble, yet the same coumarin can thin the blood and tax the liver in quantity. Keep a dog from grazing a whole patch, and call the vet if a lot goes down.
Horses Caution
A taste mixed into pasture is minor, but eating a large amount of the coumarin-rich foliage can lead to bleeding problems and a dull, off-color horse.
Rabbits Caution
A small browse is generally fine, though the coumarin means this shouldn't become a steady part of the diet. Offer only the odd sprig rather than a full feeding.
Livestock Caution
Cattle, goats, and sheep can graze a little without harm, but a big intake of the dried or fresh foliage raises the risk of internal bleeding and liver strain from the coumarin.
Birds Caution
Birds rarely show much interest, and a peck or two is no cause for alarm. Steady feeding on the coumarin-bearing leaves is the part to avoid.
People Caution
A little flavors May wine and teas safely, which is its old kitchen use. Eat it in quantity, though, and the coumarin can cause liver damage, bleeding, and dizziness, so keep helpings small.
Foliage contains coumarin, the compound behind its sweet, fresh-cut-hay scent (which intensifies as it dries). In large quantities coumarin can have blood-thinning (anticoagulant) effects and cause liver issues, and the FDA prohibits coumarin as a food additive, so only small culinary amounts are traditionally used and large quantities should not be eaten.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
There isn't much to choose between here. Sweet woodruff is grown almost entirely as the plain species.
Galium odoratum (straight species)
The plain species is what nearly everyone grows, since it carries few named cultivars and was once filed under the older name Asperula odorata.
How to propagate
Sweet woodruff multiplies with ease, whether you split an existing clump or let it seed itself around the garden.
DivisionEasy
Spring (or any time in the growing season if kept moist until established) · A few weeks to a season
Division is the easy way to make more. In spring, dig up the rhizomatous clumps, pull them apart, and replant the pieces in moist shade, where they knit back together within a few weeks to a season.
SeedModerate
Late winter to early spring; benefits from cold stratification · One or more seasons; germination is slow
The plant self-seeds freely on its own, but starting it from seed on purpose tests your patience. Sow in late winter to early spring after a spell of cold stratification, and expect slow, uneven germination that can take a season or more to fill in.
Myths
Sweet woodruff is fully edible and safe to eat in any amount because it flavors May wine.
It is safe only in small culinary amounts. The leaves hold coumarin, which in quantity can thin the blood and harm the liver, and the FDA bars coumarin as a food additive. Use a light hand for flavoring and never eat it by the bowlful.