What is Asiatic dayflower?

Getting Asiatic dayflower identification right is easy once you’ve seen one bloom: two bright blue petals stacked above a tiny white one, like a pair of mouse ears. It’s a summer annual from eastern Asia that sprawls across moist, shady ground and has made itself at home in gardens all over Pennsylvania.

Botanically it’s a monocot, related to spiderwort, even though it looks like an ordinary broadleaf weed. That matters because it doesn’t react to some weed killers the way typical broadleaf weeds do. It dies every fall, but the seed it leaves behind comes back the next summer, often thicker than before.

Asiatic dayflower identification: what to look for

Look for low, sprawling stems that are fleshy and jointed, a little like a succulent version of a grass stem. The stems lie on the ground and send down roots at the joints wherever they touch damp soil, so one plant can spread into a mat a couple of feet across.

• Leaves: smooth, glossy and lance-shaped, 2 to 5 inches long, with veins running parallel from base to tip. There’s no leaf stalk; the base wraps around the stem in a thin sheath.
• Flowers: about half an inch wide, two rounded blue petals on top and one small white petal below. Each flower opens in the morning and withers the same day, but new ones keep coming from July into September.
• Bract: each flower pokes out of a folded green leafy cup shaped like a little boat. The seed capsules develop inside it.
• Seedlings: first leaves are narrow and glossy and look almost grass-like, but they soon broaden.

Where it grows in Pennsylvania

Dayflower loves shade and moisture. In central PA you’ll find it along north-facing foundations, under shrubs, in mulched beds next to downspouts, along ditches, and in low corners of the yard where water sits after a storm. It also shows up in vegetable gardens, nursery stock and crop fields.

It’s rarely a problem in a thick, regularly mowed lawn. Where you do see it in turf, it’s usually at the thin, soggy edge of a bed or a wet spot that never fully dries out.

Asiatic dayflower look-alikes

The flower is the giveaway, but before it blooms dayflower can be confused with a few plants:

• Spiderwort: a garden perennial in the same family. Its flowers have three equal petals, and its leaves are long, stiff and upright rather than short and sprawling.
• Smartweeds like Pennsylvania smartweed: they also have swollen stem joints with a papery sheath, but their leaves have a midrib with branching side veins, and they bloom in pink spikes.
• Wandering Jew: the familiar houseplant has similar fleshy stems, but three-petaled flowers, and it won’t overwinter outside in Pennsylvania.

How to get rid of Asiatic dayflower

Hand-pulling is your best tool. The roots are shallow, so plants come up easily, especially after a rain. The catch is the stems: any piece with a joint left lying on moist soil can root again. Pull the whole plant, gather up the broken bits, and put them in the trash or a bag rather than leaving them on the bed.

• Start pulling as soon as you spot seedlings in late spring, and check every week or two through summer.
• Get every plant out before late summer, when capsules ripen inside those boat-shaped bracts.
• On larger patches, a hoe works on small seedlings, but rake up the pieces afterward.

Cultural fixes make a big difference. A 2- to 3-inch layer of shredded mulch smothers many seedlings, and dense groundcovers or shrubs that shade the soil leave less room for it. Because it thrives in damp ground, fixing a soggy spot by redirecting a downspout or regrading can take away the conditions it likes most.

Herbicides: dayflower is tough to kill chemically. University research and extension sources report it is tolerant of glyphosate, which is why it became a bigger problem in farm fields. In beds, a preemergence herbicide labeled for landscape ornamentals and for dayflower can cut down new seedlings if applied before they emerge in spring. Read and follow the product label, which is the law, and make sure the product is labeled for your site, whether that’s turf, beds or a vegetable garden. Anyone applying herbicides for hire in Pennsylvania must hold a PA Department of Agriculture pesticide applicator certification, so for big areas call a licensed lawn-care or vegetation-management company.

Keeping it from coming back

Dayflower seed can sit in the soil for years, so expect to keep pulling for a few seasons even after you’ve cleaned up a bed. The good news is each year gets lighter if you never let a plant finish seeding.

Keep mulch topped up, avoid bringing in soil or plants from a spot that’s infested, and watch the wet, shady corners first. If the whole bed is a tangle of dayflower and galinsoga, it’s often easier to strip it, fix drainage and replant than to fight it plant by plant.

Questions we get about asiatic dayflower

Similar weeds

Pennsylvania SmartweedPersicaria pensylvanicaHairy GalinsogaGalinsoga quadriradiataCommon PurslanePortulaca oleracea