Growing Bonsai Indoors

This is pretty long and I'm not sure the system will take it all, but Jerry Meislik wrote this for one of the former lives of the IBC.  It is a brief overview of what it takes to grow "Indoor" trees.  

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Growing Bonsai Indoors

Contributed by Jerry Meislik   

A bit more in depth than our other "Indoor Bonsai" article.

Throughout the two thousand or so year history of bonsai, trees have been grown in backyards and gardens. Most of the information available on growing bonsai derives from this experience with traditional temperate plant species grown in the fields and backyards of China and Japan. Bonsai in these areas were never grown in the home, but they were displayed indoors for a few days in special alcoves or tokonoma and then returned to their outdoor home.

In the last 50 years adventurous individuals throughout the world have experimented with and succeeded in growing bonsai indoors. Today, there are many bonsai enthusiasts who would like to successfully grow bonsai indoors. In order to make indoor bonsai a success, the following is a brief summary of factors to guide these adventurous souls. The following concepts should be thought of as starting points for your bonsai endeavors and not as hard and fast "rules". Home environments and trees selected will vary in each home, and the care will vary as well.


Plant selection

Most homes do not provide the best growing conditions for trees, and the result is that relatively few trees will survive for prolonged periods indoors. The most critical factor in keeping plants alive indoors is the proper selection of plant species that tolerate the growing conditions in the typical western home. Trees such as pines, and junipers as well as most of the needled evergreens will be nearly impossible to grow indoors and yet mass marketers of bonsai sell many of these trees to the uninformed buyer as suitable for indoor bonsai. Instructions, if any, included with these trees fail to mention that they require a cold dormant period to survive.

Trees selected from the tropical and sub-tropical areas of the world more often succeed indoors while temperate, frost hardy plants will not. One rough rule is that plants that normally grow outdoors in USDA zones 5 and colder will likely not tolerate indoor growing conditions. Hardcore growers in tropical countries put their temperate trees into a refrigerator to chill them down for their required period of winter dormancy.

Short List of trees.

The trees below are suitable for growing indoor and will be happy in a home environment without chilling.

Brassaia actinophylla - full sized Schefflera
Carissa grandiflora- Natal plum
Ehretia microphylla - Fukien tea
Ficus benjamina, microcarpa, salicifolia, burtt-davyi, rubiginosa etc.
Hedera helix - Small leaved English ivy
Ligustrum sp.- Chinese Privet
Ebenopsis ebano(Pithecelobium flexicaule) - Texas ebony
Portulacaria afra - Elephant grass, Dwarf Jade
Schefflera arboricola - Dwarf Schefflera
Wrightia religiosa - Water jasmine

The indoor environment

Light

Green plants obtain all their energy for their growth and biological functions from light. Plant food provides the raw materials with which plants synthesize food using the energy provided by light. Chlorophyll is the green pigment in plants that allows this magical transformation to occur.
Most homes are just too dark to sustain the life of a green plant. Plants kept in a dim room literally "starve" to death. One very rough way to judge how much light is available in a room is the ability to read small newspaper print comfortably. If the room does not have 12-16 hours of that light intensity, growing any tree will be difficult. This is the minimum light intensity that will allow plants to survive. More light allows plants to grow faster and to be healthier. Indoors, plants can not get too much light. Strive to have healthy plants that grow quickly, only then can they be styled into wonderful bonsai.

Anything that provides more light to the plants will help. A sunny window with south or west exposure will be beneficial, as will a light setup with fluorescent or metal halide lights. Increased light will allow success with a wider range of tree materials. Very few plants will survive indoors in dim light. If your home is dim and you cannot provide additional light, the only plants that may live are Brassaia, Schefflera, some Ficus, and ivy. Even these "low-light" plants will grow slowly and their trunks will thicken ever so slowly. Under low light internodes will be long, and leaves will be large. This is not conducive to long term bonsai success.

The most easily obtained source of light is a common fluorescent light fixture, two to four feet long, that is situated at the very tops of the trees. The closer the bulb is to the plant, the more energy the plant absorbs. Use a timer to keep the lights on for 10-18 hours each day. Use warm or daylight fluorescent bulbs or mix the two types of bulbs.

Metal halide lights also work well, but they generate heat and the plants cannot be kept too close to the bulbs or the leaves will burn. Metal halides also require a transformer box for each bulb. These lights do provide lots of bright light that is excellent for plant growth.

Another light source are incandescent bulbs, but they are inefficient and throw off lots of heat. They also tend to have small areas of coverage so a large area with plants is very difficult to illuminate.
Special grow lamps with frequencies balanced for plants are more expensive and probably not worth the extra cost. If money is no object, consider these full spectrum bulbs as they provide light that is said to encourage more flowering and fruiting.

Humidity

Indoors the air is very dry, and humidifying the air in the plant area will help greatly. Place a humidifier close to the plants to moisturize the air. Cool or warm humidifier units will work equally well. Humidity levels of 30-50% will help plants grow more strongly.

Frequent misting and humidity trays full of water underneath the trees may help, but make sure to keep the plant's roots above the water, and not sitting in it. Misting may also encourage fungal problems on susceptible plants.

Some growers erect a plastic tent around their trees to increase the humidity level near the trees, but some area of the plastic tent must remain open to prevent fungal problems.

Ventilation

Ventilation and air movement in most homes is not adequate for trees. An oscillating fan that circulates air around the trees will help keep fungal and other pests under control. Try to have enough air movement to see the leaves move slightly.

Temperature

Most homes have a temperature range of 60-90 Fahrenheit and this should be suitable to most indoor trees. Avoid chilling tropical trees with temperatures below 55 as they may suffer or die, or allowing the trees to get warmer than 100 degrees.

Some sub-tropical trees will appreciate a cool, humid rest period in the fall. Trees that will benefit from this include elm, cotoneaster, ivy, crape myrtle, olive (Olea), citrus, and Serissa to name just a few. If you intend to keep a juniper alive indoors, be sure to allow the juniper to have a cool rest period for 6-12 weeks. Temperatures below 50 Fahrenheit will work the best.

Soil, Fertilization, Watering

Indoor growers do not need to modify the usual soil mixes, fertilization and watering procedures used for outdoor bonsai. However, it is best to avoid organic fertilizers as these may result in attracting insects that live on the decaying materials.

Indoors trees are not subjected to periodic overhead, drenching rain showers. It is quite helpful to spray all tree surfaces with water every week to keep the leaves and trunks clean and to discourage insects. Move trees to the sink or bathtub and use a gentle spray with warmish water to refresh the plants.

Insects

Insects are often a major problem for indoor growers. Two factors seem to aggravate the insect problems. One, the lack of beneficial insects to keep the pests under control, and two, the constant temperatures, lack of wind, sun and rain that hold insects in check in the outdoor growing area.
Specific insecticides for indoor use should be thoroughly investigated due to potential toxicity to human inhabitants, as well as toxicity to some trees. See IBC Pests section on treatments for insects, and always read and follow labeling on pesticides.

Many growers use a simple mix of liquid dishwashing soap in water as a pesticide spray. Other growers use a dilute solution of dormant oil. Each and every spray will be toxic to some plant, so it is best to always test spray an expendable plant or branch. Spray that plant or branch and then wait 7-14 days to see if any damage is apparent. If there is damage, select another spray for that type of tree.

Selecting trees for indoors

Under even the best indoor growing conditions trees will grow much more slowly than in suitable outdoor conditions. With this is mind, it is necessary to buy as much tree as you can afford, since trunks thicken ever so slowly indoors.

Also, select trees with small leaves, since large leaves will be out of scale with the smaller sized trees that are normally grown indoors.

My personal indoor growing room

My indoor growing setup in Montana is a 20 by 20 foot room of the house that has been modified to serve as a "greenhouse". The snowfall in our area is about 250 inches a year, making skylights and a conventional greenhouse impossible. The roof of my plant room is covered with conventional shingles and has no skylights, and the windows are normal house windows. Light is supplied by the transmission of some outdoor sunlight through the windows, but the main light supply is from metal halide lights suspended from the ceiling. There are nine, 1000 watt metal halide bulbs in total and they cycle on and off automatically with a timer set to provide a 10 hour day. I do not vary the length of day seasonally. The plants never leave the room as the outdoor temperatures are too cold on many evenings even in the summer.

Moisture that evaporates from the soil in the pots keeps the humidity high, so humidification is not needed. Excess humidity is a problem in that the windows often have condensation. A humidity controlled exhaust fan removes saturated air in the summer as well as feeding it into the house in the winter.

Our tap water is hard and mineral laden and not good for plant growth, so a reverse osmosis water system provides pure water to the trees and keeps salt buildup to a minimum.

Soluble chemical fertilizers are applied weekly at half strength, as well as the application of timed release chemical fertilizers applied every three months. Fertilizers are purchased when on sale and not by brand name. Organic fertilizers are not used.

Insects can be a major problem in the greenhouse and this takes vigilant observation and treatment of infected trees before damage is done. Typical pests are scale and spider mites. Mites have been particularly troublesome at times. New trees are never brought into the greenhouse until they are observed and sprayed for insects. Friends trees are never allowed into the greenhouse.
Several fans keep the air moving around the trees. Pests are discouraged by good air movement.

Conclusions

Although indoor bonsai is not traditional, it is a wonderful addition to the bonsai hobby, and it is especially important to those who live in the city and those who can not find space for outdoor bonsai or those who just want that great feeling of having a bonsai share their home.

Good luck on your adventures with indoor bonsai.

Special thanks to Carl Rosner for reviewing, editing and contributing material to this article.
Jerry Meislik. www.bonsaihunk.8m.com

Thanks Jim.

water jasmine is an under-utilized specie in bonsai - i've seen incredible specimens in greenhouses, but not many bonsai. anyone worked with this specie much?

Outside the USA, water Jasmine is the primary bonsai in Singapore and probably Malaysia. It's everywhere, even in the nurseries.

There are indeed incredible specimens. Leaves and roots grow fast, and almost every style can be made with it. Tough plant too. I like the jasmine scent, one little tree with flowers can fill a room with its fragrance. I have since moved mine outdoors though, they produce so many little flowers that when they drop, there's a lot to clean up, or ants will surely come.

great to know brett.... do you know how they're usually propagated?

For those who don't know, I have been growing plants indoors most of my life. I have been growing under fluorescent lights 53 years, bonsai about 25. I concur with most of what Jerry said, but would like to add a few points.
Unless you live in Montana, you will have much better success if you put your bonsai outdoors for the summer. Just put them out gradually in the sun until they are getting all they will tolerate.
I found the big drawback with water jasmine is that it can't be grown in a group planting with other species. It kills them, like black walnut.
Under my conditions, I found that you do have to adjust your soil mix for growing under lights and then outdoors for the summer. It must be very well drained. The trees that like to dry out, like Ficus, thrive with a very coarse mix such as you would use for conifers. Of course you have to water more often. I add SoilMoist crystals to all my potting mixes.
I keep my lights on 18 hours. I also grow orchids, and some of my conditions cater to them.
Some bonsai require higher humidity. Serissa prefers about 65% and Ficus sycomorus revels in orchid conditions with 70% humidity.
I rarely grow indoor bonsai in windowsills, since Syracuse is one of the cloudiest cities in the country. Ficus benjamina 'TooLittle' and monkey-thorn, Senegalia galpinii, do well. But remember, they go outdoors in the summer. My quasi-bonsai, pygmy date palm, does fine on a table in the cool guest room for the winter.
Iris

Kirk, they are easy to propagate, almost all - seeds, cuttings, air layering ...

Like when it flowers, and you leave them alone, seeds soon come after the flowers drop, then the seeds drop into the soil and they can actually sprout quickly.  They also tend to have a lot of suckers, and one can take these as cuttings.

They like a lot of water, but still can survive even if watered less (like I do).  

The Vietnamese have a small-leaf variety, that should be a good one.  Of course, one can make the normal Wrightia Religiosa (Shu Mei) have small leaves.  There are also variegated ones with a different flower, as well s variegated ones with the same flower.

Pruning is like for maple, the leaves even come in pairs.

kirk@localbonsai.com wrote:great to know brett.... do you know how they're usually propagated?

9000 watts of metal halides will grow almost anything indoors. In a 20' by 20' grow room here in Michigan I have a room with 10 one thousand watt m.h. lights. You need sunglasses to go in there! I have an elm in there right now and its thriving. Also some monster elm cuttings that are rooting. Just hunks I put in soil and kept moist. Been there for over a month and already are branching out.

Alas, the standard 4 foot 40 watt fluorescent lamps are obsolescent. They say the tubes may not be available shortly. I am too old to retrofit my plant room to T5 or LED. It would be very expensive. I think I had better stock up on another case.
Iris

Mr Frary,

Can you offer me any recommendations for building an economical metal halide set-up, i.e. 1-2 hundred bucks ? Or is this unrealistic ? My indoor trees are not thriving on fluorescent tubes.

Thanks,
-Kirk

Do you use the high K Daylight tubes?
Do you put your trees outdoors for the summer? Jerry Meislik has to use metal halide lamps because in his part of Montana, they can have frost every month of the year.
Do you add humidity to your growing situation? Some tropicals require extra humidity.
Iris

Thanks for the info.!!!!