Carmen is a horticulturist, specializing in bonsai care and design. She has been with MBGNA for 15 years and has been doing bonsai for 13 years. Carmen apprenticed with bonsai professional Michael Hagedorn of Crataegus Bonsai in Portland, Oregon. Outside of work, Carmen co-hosts the podcast, Little Things for Bonsai People, and is a co-founder of the Purple Pot Society, which inspires and educates women in bonsai.
Most days when I’m outside working in the bonsai garden, I’m approached with the questions, “Can I grow bonsai indoors?” and “What species grow best indoors?” My standard answer is, “Because bonsai are trees and shrubs, they need to be grown outdoors.” This is true, even in the case of tropical bonsai. However, because tropical plants cannot withstand our cold winter temperatures here in Michigan, they have to be brought indoors once temperatures begin to drop. And for many people, limited access to outdoor growing space means indoor growing is the only option. While growing bonsai outdoors is generally the best option, tropical bonsai can be grown successfully indoors with the proper set up and care.
What is Bonsai?
Bonsai are trees or shrubs that are grown in a pot. A common misconception is that “bonsai” itself is the species, or variety, of tree. “Bonsai” is a Japanese word that means “tree planted in a pot”. It is a set of techniques that, when applied to a woody plant, create a miniature representation of a tree in nature.
These techniques were developed over hundreds of years, beginning in China and travelling to Japan, where modern bonsai techniques were mastered and popularized. Almost any woody plant species can become a bonsai when designed and cared for properly.
Caring for Bonsai Indoors
While most bonsai are best grown outdoors, several tropical species can be grown successfully indoors with proper care and realistic expectations. Ficus species are one of the easiest bonsai to grow indoors. They can tolerate lower light levels and humidity than many other tropical species. Other popular indoor species include dwarf jade (Portulacaria afra), fukien tea, (Carmona sp.), and dwarf umbrella tree (Heptapleurum arboricola previously called Schefflera arboricola).
The biggest concern when growing bonsai indoors is light. Plants “make their own food” by capturing light energy from the sun and transforming it into chemical energy for their own use through a process called photosynthesis. Without light, plants cannot grow or thrive and will eventually weaken and die. Different plants require different light intensities. Many tropical species grown for bonsai are understory trees or shrubs that are adapted to lower light levels which make them ideal for growing indoors. Even so, when indoors, supplemental light is often necessary. LED and fluorescent grow-lights are the most readily available, affordable, and practical option.
Grow lights should be placed 6-12 inches above the bonsai. If the light is too close to the bonsai, it can damage the leaves. If the light is too far away from the bonsai, it will not deliver the optimum light intensity to the tree. Most hobby grow-lights will not emit enough heat to be concerning, but do be aware that grow-lights can emit heat that could damage leaves or cause a bonsai to dry out more quickly.
Temperature is the number one reason tropical bonsai are brought indoors to grow over winter. When nighttime temperatures begin dropping to 55 degrees fahrenheit and below, it’s time to bring tropical bonsai inside. Likewise, once nighttime temperatures begin to rise above 55 degrees fahrenheit regularly, tropical bonsai can go back outdoors. Keep tropical bonsai away from vents as direct airflow in winter will dry them out quickly and direct contact with air conditioning in the summer months can chill them. If the tropical bonsai is kept near a window, be aware of seasonal temperature fluctuations that may scorch a tree in the summer months or chill a tree in the winter.
Water needs of a tropical bonsai will change when moved indoors. Lower light levels and less air movement can prevent bonsai from drying out as quickly as it might outdoors. Alternatively, a less humid environment inside the home may cause the tree to dry out more quickly. Pay attention the first couple of weeks indoors to see how the tree might respond to the change of location. Check the bonsai for water every day, but only water when needed. Fertilize regularly to maintain current growth and encourage new growth.
Tropical plants generally prefer more humid environments. Tropical bonsai benefit from humidity, but some species can tolerate lower humidity than others - ficus and dwarf jade are two examples. To increase humidity, add a humidity tray underneath the tropical bonsai, run a humidifier, or mist the bonsai a couple of times per day. Mini portable greenhouses are also an option to help retain humidity and moisture.
When moving a tropical bonsai indoors, or when changing its growing environment drastically, its leaves may turn yellow and/or fall off. This is normal. Many tropical bonsai grow leaves to optimally function in their environment. For example, a ficus grown in full sun will have thicker, waxier leaves than a ficus grown indoors. If that ficus is moved indoors, those leaves no longer function as well in the lower light environment. They will fall off and new, thinner leaves will grow to replace them. If this happens, use care to not overwater your bonsai. When a tree doesn’t have leaves, water is not absorbed as quickly, and overly moist soil will cause root rot.
Common Indoor Pests
There are a few pests to watch out for when growing tropical bonsai indoors. Aphids, scale, mealy bug, and spider mites are the most common -
Aphids are soft-bodied sucking insects, often pale green in color. They can also be brown, black, or red. They secrete a sticky substance called honeydew, which may attract ants or cause the growth of sooty mold - a fungus that appears like soot on leaves and branches. Aphids can be washed off with insecticidal soap or treated with a contact or systemic insecticide.
Scale insects are sucking insects that appear as brown or white bumps on leaves and stems. They also produce honeydew. These can be manually removed with a cotton swab dipped in alcohol or treated with a horticultural oil or systemic insecticide.
Mealy bugs are another sucking insect that can be found on leaves and stems of bonsai. They have a white cottony appearance. They can be manually removed with a cotton swab dipped in alcohol, insecticidal soap, horticultural oil, or a systemic insecticide.
Spider mites are tiny arachnids that range in color from red to brown to white. They are difficult to see with the naked eye, but they cause visible symptoms on a plant. Leaves will begin to look pale and dry out, and webbing will form between leaves. Spider mites can be removed by regularly spraying a tree with a strong spray of water to manually remove them. They can also be controlled with insecticidal soap or a miticide.
A Few Final Tips
Growing bonsai indoors comes with its challenges, but with the right expectations and a little attention, it can be deeply rewarding. Ultimately, successful indoor bonsai care is about observation and adjustment. By learning how your bonsai responds to its environment and making small, thoughtful changes, you can enjoy the beauty and practice of bonsai year-round, even in a Michigan winter.
