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As a child, I was fascinated by sensitive plants. I loved to rub my fingers along the stems to see the leaves close. At the time, I thought that they were carnivorous plants like Venus Fly Traps, but it turns out that the leaf closing is a defensive measure.
Sensitive plants (Mimosa pudica) are also called Zombie Plants or Touch-Me-Not. They are woody perennial shrubs that are native to Central and South America. They have since spread to Southern and Eastern Asia as well as the southern United States. They are considered an invasive species in those areas because they are aggressive spreaders. Outside of the tropics, they are grown as annuals or as houseplants.
Sensitive plants are members of the legume family, related to peas and beans. Legumes are referred to as "nitrogen fixing" plants. They have nodules on their roots that enable them to take nitrogen from the air and convert it to a form that can be used both by the legumes and the plants around them.
Sensitive plants got their name from their ability to close their leaves when touched or shaken such as by a strong breeze. This is thought to be a defensive measure to prevent herbivores from eating the plants. Supposedly the movement startles them and they go looking for a less “active” plant to eat. The leaves, which grow in a parallel row along the stem, open again within an hour.
The shrubs grow to 5 feet. At first they are upright, but as they get taller, the branches tend to fall over and the plant appears to be growing along the ground. They are characterized by thorns on their stems and branches and their unique flowers which resemble a dandelion that has gone to seed. The fluffy flowers can be yellow or purple. They are both wind-pollinated and insect-pollinated.
When they are pollinated, they produce a cluster of 2 to 8 seed pods that are ½ inch in length. Each pod contains 3 or 4 seeds. The seeds have very hard coats. It is thought that it is high temperatures such as during a tropical summer that stimulate the seeds to germinate.
Sensitive plants are only hardy in growing zones 9 – 11. The rest of us have to grow them as houseplants. The plants need full sun. They cannot tolerate any shade. They prefer very poor, well-drained soil. The reason that they can live in poor soil is because they make their own nitrogen, often missing in poor soils, thanks to the nodules in their roots which convert atmospheric nitrogen absorbed through their leaves into a form that the plants can use.
When grown indoors, they grow best under lights. If you don’t have grow lights, place your plant in your sunniest window.
Grow them in well-drained soil. Add some peat moss or coir to your mix to maximize the drainage. Water them enough to keep the soil moist but not too wet. The roots will develop root rot if the soil is too wet.
Although in nature, sensitive plants grow in poor soils, when grown in a container, they will require a little fertilizer. This is because when you water a container, the water that flows out of the drainage hole takes nutrients with it. Unless those nutrients are replaced, eventually all of the nutrients in the soil will be leached out.
Since sensitive plants can make their own nitrogen, you only need to replace the potassium. Water your plant first, then water with a liquid potassium fertilizer diluted to half strength. Do this every two weeks during the growing season. The reason why you must water your plant first is to avoid burning the roots with the fertilizer.
Sensitive plants are easy to grow from cuttings. Take a cutting from a branch that is at least 4 inches long. Dip the end into some rooting hormone and then gently press it into a container filled with moist soil. These are tropical plants, so you will need to provide a warm moist environment for them. Place a plastic bag over the pot to provide the necessary humidity. Place the container in a sunny window in a warm room that is at least 65⁰F. You will know that roots have formed when you see new growth on your cutting, in about 2 to 4 weeks.
Growing a sensitive plant from seed is a little more labor intensive that growing from a cutting. The seed coats are extremely hard. To soften them up, you can either soak them overnight or nick them with a knife. Nicking the seeds makes a small opening where water can get in to start the germination process.
Surface sow your pre-treated seeds in a container with moist soil. Don't cover them. They need light to germinate. Keep the soil moist but not wet. Germination should occur within a week. Seeds that have not been soaked or nicked can take up to 2 to 3 weeks to germinate.
© 2019 Caren White
Alexander James Guckenberger from Maryland, United States of America on July 15, 2019:
My uncle's mom grows these.