Garlic Mustard

Quick facts

For identification. Not a growing guide.

How to recognize it in each season.

1. 1

   Year one: the spring germination flush

   Mar to May, every year

   • Seedlings come up in a carpet, all at once
     Garlic mustard seed needs a winter of cold before it will germinate, so it arrives as a dense flush of seedlings in early spring - often hundreds per square foot under a parent plant. Seedlings show two smooth kidney-shaped seed leaves, then round, scalloped true leaves that already smell of garlic when crushed. A carpet of small round-leaved seedlings under last year's dead stalks is the classic sight.
   • Seedlings are the cheapest ones to remove
     A seedling flush can be scuffed out with a hoe or a boot sole, or smothered under cardboard and mulch in a garden bed, at a fraction of the effort a second-year plant costs. This is the moment where an hour of work is worth ten later - but do not till, which buries seed at depths where it survives longer and simply spreads the problem across the bed.

   Key signs

   • Dense carpets of round-leaved seedlings in early spring
   • Seedlings clustered under last season's dead flower stalks
   • A garlic smell from crushed seedling leaves
2. 2

   Year one: the green winter rosette

   Jun to Feb, every year

   • Recognize the rosette: kidney-shaped, scalloped, green all winter
     The first-year plant is a low rosette of dark green, kidney-shaped to round leaves with scalloped edges and a wrinkled surface, on long stalks. It stays green through winter, so a patch of green rosettes in a bare December woodland is nearly always garlic mustard. Crush a leaf: garlic. Nothing else with that leaf shape smells like that.
   • Late fall and early spring are the selective windows
     Because the rosette is green while native woodland plants are dormant, late fall and very early spring are when you can work on it without collateral damage - hand-pulling, or a foliar herbicide treatment where the infestation is too big to pull. Use a product whose label lists the site you are treating and follow that label; it is legally binding. In floodplains and along streams the product must be labelled for aquatic sites, and many states require a permit or a licensed applicator.
   • The rosette is also the best eating
     First-year rosette leaves, picked in late fall or very early spring while it is cold, are the mildest and best-tasting stage of this plant - garlicky and only lightly bitter. The first-year root, dug at the same time, grates like a mild horseradish. Take what you want from a patch you are about to remove, from unsprayed ground, and pull the whole plant rather than picking leaves off one you intend to leave.

   Key signs

   • Green rosettes in a bare winter woodland
   • Kidney-shaped scalloped leaves that smell of garlic when crushed
   • Rosettes spreading outward from an established patch
3. 3

   Year two: bolting and white flowers (the pull window)

   Apr to Jun, every year

   • A stalk with triangular leaves and small white four-petalled flowers
     In its second spring the rosette bolts into a stalk one to four feet tall. The leaves change shape as it climbs - triangular to heart-shaped with coarse teeth - and it opens clusters of small white flowers with four petals in a cross, the mustard-family signature. It still smells of garlic. The root has a distinctive S-shaped crook just below the crown, which is a useful confirmation when you pull one.
   • Pull it now, whole, and bag it
     This is the deadline. Pull second-year plants from moist soil, grasping low and lifting steadily so the crooked root comes out with the crown - a snapped stem resprouts and flowers again. Bag every pulled plant into the trash. Do not compost it and do not leave it in a pile: a pulled flowering plant will finish ripening viable seed on its own stored moisture. Work outward from the satellite patches toward the dense core.
   • Where you cannot pull, cut at ground level at peak bloom
     On steep or rooty ground where pulling causes more damage than it prevents, cutting works - but only cut at GROUND level, and only at peak bloom. Topped plants simply branch and flower again lower down. Because it is a biennial that dies after flowering, a clean cut at the base at full bloom kills the plant outright. Bag the cut tops.
   • Young stalk leaves, buds and flowers are still worth eating
     Before the pods form, the young upper leaves, flower buds and open flowers are good food - more bitter than the winter rosette, and better blanched thirty seconds and drained before use. Eat what you pull; do not make a second trip to a patch you have not cleared.

   Key signs

   • One- to four-foot stalks with triangular toothed leaves
   • Clusters of small white four-petalled flowers
   • S-shaped crook in the root when you pull a plant
   • Snapped stems resprouting and flowering lower down
4. 4

   Year two: seed pods (the point of no return)

   Jun to Aug, every year

   • Slender upright pods, then a shower of black seed
     After flowering the plant sets siliques - slender pods two to three inches long held stiffly upright against the stem. They ripen from green to straw brown and split, flinging small black seeds several feet. The dead stalks stand through the following winter, which is how you find last year's patches. Once pods are browning, the seed is largely made and the year is lost.
   • Bag pods where they stand - do not shake them loose
     If you find pods, cut and bag stems carefully rather than yanking them, which shatters ripe pods across the ground. Slide a bag over the top of the stalk before you cut it where you can. Everything goes in the trash, never the compost. Then mark the spot: you now know where next spring's seedling flush will be, and that is where to spend April.
   • Clean your boots, tires and dog before you leave
     Seed travels on mud - on boot treads, bike and ATV tires, mower decks, hooves, and dog coats - which is how it jumps from a trailhead into an untouched woodlot. Brush off before you leave an infested site, and again before you enter a clean one. This costs nothing and prevents the kind of long-distance jump that hand-pulling can never undo.

   Key signs

   • Slender upright pods along the upper stem
   • Pods browning and splitting (seed shed has begun)
   • Standing dead stalks marking last year's patches
   • Seed carried on boots, tires, mowers and pets

Watch out for

4 to know. 2 are high-risk: Allelopathy & Mycorrhizal Disruption, Seed Bank & Pulled-Plant Seed Ripening. 2 are active in September.