Grow on still water in full sun to full shade. Scatter small bunches of plants on the water surface after last frost date. Spreads quickly in optimum conditions. Grows best in the cool temperatures of spring and autumn. Net out excess plants as needed. Can be quite invasive in frost-free climates. As waters recede, duckweed can grow on wet mud. Plants develop buds (turions) in autumn that sink to the bottom of the body of water for overwintering. Buds rise to the surface in spring only after water temperatures warm up
It's very useful in nature, a high-protein plant that makes excellent food for fish, waterfowl, & wildlife. It has also proven useful to science for cloning & genetic experimentation & for assessing the health or pollution levels of watersheds & other natural environments.The European space program is experimenting with duckweed as a possible food resource for extended stays in outer space. It is already being used for organic sewage treatment & purification of agricultural wastewater. Duckweed grown on pools of sewage are not toxic & can be skimmed & processed as food for farmed fish or livestock, or it can be used as fertilizer mixed with soil.
 In herbal  medicine
 Duckweed –antipyretc, diuretic, desensitizing, antimicrobial.
It is purposed in treating of nettle-rush, vitiligo, asthma, upper air passeges inflammation.
Outward use: rheumatism, podagra.