Also known as Asian dayflower, this summer annual weed is a member of the spiderwort family, Commelinaceae, and is native to most of East Asia and northern parts of southeast Asia, where it grows in moist, open places, such as shady forest edges and wet areas of cultivated fields. It was introduced into the US probably for horticultural use and has spread along the East Coast from Maine to Georgia and west to North Dakota and Texas. Several states consider it a noxious weed but some gardener like the bright blue flowers and encourage its growth especially in woodlands. Plants prefer a fertile, moist, loamy or sandy soil and partial sun, but tolerate full sun. Photo Credit: NotAnonymous, Wikimedia Commons
Description: Growing 1-3′ tall or long, common dayflower can be erect or prostrate. The stems are well branched, fleshy, and root at the joints. The alternate green leaves are lanceolate to oblong, 2-4″ long, and clasp the stem. The flowers appear singly or in small clusters in leaf axils from mid summer to early fall. Each flower is 1/2-1″ across and consist of two large, bright blue petals at the top and a single smaller, notched, white petal below, 3 membranous sepals, 5-6 stamens, and a long white style. All petals are enclosed in a leaf-like bract called a spathe. The flowers are open for only one morning and give way to 2-celled fruit capsules containing 2 brownish to red wrinkled seeds in each cell. Plants spread primarily by seed but may form colonies when roots form at the joints of the stems. The seeds can remain viable for up to 4.5 years and can germinate any time of year.
Control: Dayflower is difficult to eradicate because of the long viability of the seed and the resistance of the plant to most herbicides. Hand pulling is effective and should be done before seed set and when the soil is moist so the whole plant can be removed without breakage. In severe cases an herbicide containing the two chemicals, Cloransulam-methyl and sulfentrazone, can be used with some success.