The delicate-seeming Mimosa pudica is also called the “touch me not,” and “sensitive plant” because when it is touched its leaves fold up. The leaves not only do this in response to touch, but with sudden differences in temperature and light. The entire plant seems to droop if the stems are touched, and when night comes all of the leaves fold as if the plant is calling it a day. This is called nyctinasty. Scientists believe that the plant does this to protect itself from external threats.
When a person asks “what is mimosa?” the answer is that it’s a member of the pea family. It’s native to Central and South America, but is now found in other warm climates such as the southern parts of the United States, southeast and south Asia, the Caribbean, the Pacific Islands, western Australia and some African countries. In many places, Mimosa pudica is considered invasive, but some gardeners welcome it because of the beauty of its leaves and flowers. Other people seek the plant out because it has medicinal properties.
What Does the Plant Look Like?
A Mimosa pudica seedling has an erect stem, but as it gets older the stem flops over and trails or creeps. Stems can grow as long as 5 feet. Sometimes they are prickly enough for people to avoid walking over the plant in bare feet. The leaves are pinnate, or feather-shaped. The leaflets that grow on them are also pinnate, which gives the foliage a fernlike look. The flowers are held up on stalks and are soft pink or purple, and more and more appear as the plant ages. The flower heads are round or oval and pollinated by both insects and the wind. They develop into segmented pods that hold pale brown seeds. These seeds are hard and, despite the plant’s reputation for invasiveness, hard to germinate.
Growing Mimosa Pudica
If a gardener lives in a warm climate, the sensitive plant is easy to grow. Indeed, it may be too easy to grow. Because it propagates so quickly, it is a good idea to grow it in a pot so it doesn’t take over the garden. Other gardeners don’t mind growing the plant as a ground cover. Best of all, kids find the ability of these plants to close up at the slightest touch amusing. In this they seem to be more animal than plant, and scientific experiments have shown that the plant can learn and remember. For example, when scientists sprinkled water on a mimosa plant, its leaves closed up at first. After repeated sprinklings, the plant stopped closing its leaves and didn’t close them up even after a gap of a month between sprinklings. This told scientists that the plant had learned that the water was not a danger to it, and it no longer had to close its leaves to protect itself.
Soils where mimosa grow freely tend to have an overabundance of potassium and nitrogen. Its roots also make carbon disulfide, which kills pathogens and fungi from growing around them. As a member of the pea family, Mimosa pudica has the ability to fix nitrogen. This means it has bacteria in its roots that change nitrogen found in the air into usable nitrogen in the soil. Perhaps because of this ability, Mimosa pudica thrives in soil that is poor or disrupted as long as it has good drainage. The plant needs full sunlight and is tender to even light frost. Unless it is grown indoors, it doesn’t do well in areas where the temperature falls below 55 degrees Fahrenheit.
Because the seeds are hard to germinate, the gardener can speed up the process by scouring them, though gently. The seeds can also be placed in water for a day or so. Then, they should be rinsed to remove the chemical that kept them from germinating and planted in a pot with average potting soil. To help with drainage, place bits of a broken terra cotta pot around the drainage hole before filling the pot with soil. Plant the seeds no more than a quarter of an inch deep and water. When the plants finally sprout, water regularly, but be careful not to overwater.
The mimosa needs lots of sunlight, so put it in a southern window or under a gro-light if they’re grown indoors. They do best in temperatures between 70 and 85 degrees Fahrenheit, though they can tolerate temperatures that are just a little cooler. Potted plants that are outdoors can be brought in if the temperature gets too hot or too cold.
Mimosa pudica also has the ability to pull pollutants such as arsenic, lead and other heavy metals out of the soil.
Medicinal Uses
Mimosa pudica should not be eaten because it is somewhat toxic. However, its roots, leaves and flowers can be used to make topical medicines. The plant has an alkaloid called mimosine, which either kills cells or stops them from growing and reproducing. This makes it a good antibacterial agent. It also contains antioxidants, which protect cells by neutralizing damaging free radical oxygen molecules. Mimosa also has tannins, fatty acids and sterols, and the leaves contain a chemical that resembles adrenaline. It is effective in neutralizing cobra venom and eases migraine headaches.
One way to use Mimosa pudica topically is to make a poultice out of the leaves, roots and flowers. Use a mortar and pestle to crush them, or put them in a blender with a bit of wheat germ or olive oil. The parts of the plant can be dried, crumbled and turned into a paste with water or cider vinegar. Spread the poultice on a piece of clean cloth or gauze, and put it directly on the affected area. Cover it with plastic wrap to keep it away from bed sheets and clothes, and leave it on for 24 hours. The patient may feel some discomfort as the poultice draws out the inflammation, but when the discomfort stops, the poultice has done its work.
Mimosa pudica is a fascinating and beautiful plant. Many of its secrets and powers are still to be discovered, though it’s been used in traditional medicine for thousands of years. But in the meantime, the mimosa, with its elegant, bright green leaflets and sweet purple flowers, is a wonderful addition to the garden or windowsill.