How I Grow Bonsai Indoors

by Dustin Mann

Ann Arbor, Michigan


I was born in Cleveland, Ohio in 1946.  At the age of 18 while on a family vacation to Miami Beach, Florida I developed an interest in tropical trees. In 1972 I bought a Dracaena plant and later moved on to palm trees and grew them indoors, under spot grow-lights. My first plant love was the Palm family – especially  those with orange or red crown shafts ( like the Ceiling Wax and Bottle Palm). I was most fascinated with their trunk base and bark. Perhaps an early indication of my shift into bonsai?

Dustin with assorted plants, 1989.


In 1975 I moved to Ann Arbor, Michigan and tried to dwarf and even occasionally to defoliate a “newer” fig tree being used in indoor malls called Ficus microcarpa, also called nitida or retusa. I grew it in a shallow clay pot under skylights, used a humidifier, as well as 6-8 grow lights.

By 1989 I purchased metal halide lights from a hydroponics store and all of my plants growth accelerated and it was off to the races. My interest in bonsai remains in sub-tropical/tropical trees.

My other obsession/hobby has been running/race walking for the past 47 years. I am currently and have been a school, clinical psychologist for the past 36 years.              


Of the trees that I grow my favorite bonsai are Ficus microcarpa followed by Ficus salicaria (nerifolia) as a close second. I love their appearance of old age, especially the root flare (nebari) and their vigorous growth given sufficient light.

Fig trees can be styled in many ways, tolerate horticulture mistakes, and have extreme vigor, producing new leaves following defoliation or trunk reduction. An increase in trunk girth of several inches can occur in 5-7 years under my growing conditions. Other favorite species that I grow include Bougainvillea, Portulacaria afra, Buttonwood, Sageretia theezans, Serissa, Boxwood, Schefflera, and Erodium. These trees (with the exception of Erodium and Serissa) respond favorably to heat, bright light, and humidity, as well as being able to withstand some dryness when not in active growth.

Boxwood on a rock.


Unfortunately not all trees respond well to my growing conditions.  I grew a Brazilian Rain tree, Pithecellobium tortum, for about 4 years and especially loved the dense growth of leaves and feeder roots. It needed constant watering, coupled with cooler evening temperatures. If not watered until later in the day the roots would remain dry for a long time period resulting in an unhappy tree. I also do not grow Fukien Tee, Black Olive, Privet, Crape Myrtle or Lantana due to their preference for horticultural conditions other than what I can provide.    

Brazilian rain tree.



Growing Conditions


Initially I grew all my plants indoors and then placed them outdoors for the warmer summer months. I then moved to growing plants indoors with supplemental metal halide lights.

At one time I had my trees growing in a basement under metal halide lights.


I now grow my trees in a 15 foot by 10 foot Four Seasons Company greenhouse. It has sturdy double pane glass widows, horizontal sliding doors that can be opened, motorized vents, and a dedicated hot water heater.

View into the greenhouse from my living room.


All my plants remain in the greenhouse all year long.

All trees are on moveable carts.

From 1998 until 2002 I experimented with moving my trees outside to the deck during the summer. I discontinued this because the night-time low temperatures in southeast Michigan (37th parallel) would drop below 58 degrees approximately 80% of the days and would not rise above 70 degrees until the afternoon of the next day. I have noticed less stress/insect infestation with the more consistent temperatures from leaving the trees indoors. Another possible difference is that the pots can get quite hot (over 120F degrees) in summertime when exposed to full sun outdoors.


The greenhouse faces south so there is natural daylight and this is augmented with two 1000 Watt Metal Halide lamps that are on for 16-18 hours each day. From June until Aug. 15 the lights are on for only 8 hours - because of the heat they emit.


In winters (December-March) the hot water heater is cranked up to 78-85F during the day and temperatures can drop to about 55-65F at night. Sometimes near the widow glass in early mornings the temperature reading will dip under 50F. This cooler micro-climate is where I place any Serissa, Sageretia and Erodium.

In summers the window sliders are opened and the motorized vents are set to open at 75 degrees to ventilate excess heat. Even during the winter I will open a window a few inches for 4-6 hours. Because of the motorized vents and fan I do not run a portable fan.                                                                                                                                                


The trees are watered with water from a reverse osmosis watering system because our local water is quite hard. Larger trees are watered daily - year round. Some of the smaller (shohin) trees are watered twice a day. I water with a garden hose and excess water runs off on the tile floor. Although watering is done freely even against windows, caution is made to not let water touch halide lamps or reflector hoods.


My soil is about 80-85% red-lava rock and the remainder orchid bark. I found that pine chips were not easily wettable and also had white salt deposits develop on it over time. I also use a tropical pre-packaged mix [consisting of turface, grit, pine bark] plus soil conditioner for cuttings, air-layers, etc.


Because of the surrounding glass and the size of the greenhouse containing a large number of trees I do not try to increase or control the humidity. After watering trees the humidity reading will be at 80% in winter for 1-2 hours. It never drops below 50% in winter. In the summer with windows open it will be about 80-90% in the morning, with dew on trees, but it can drop to below 40% in the afternoon on hot sunny days.                                                                                                                                                                       


Due to my inorganic soil mix, I am using organic slow-release granules from New England Bonsai (4-6-4 NPK) on top of the soil as well as incorporated into the soil on re-potting. I have not seen as many flying gnats nor the "smell" since I switched from Bio-Gold.

I augment with liquid Neptune Fish Emulsion every 5-10 days unless a tree is sick, defoliated, or newly re-potted. Neptune Harvest fish emulsion is the only one that is not pasty, and does not seem to clog my sprayer.

The fish emulsion does smell for a few hours but increasing ventilation by opening windows a crack helps. Bat Guano, Seaweed, or Dyna-Grow all smelled horrible. Dyna-Grow also develops crystals on the lava rock that looked like silicon.

I suspected that some of my previous other feeding regimes did not have even/consistent ratio of application to the soil area.

I started using Ironite Mineral Supplement powder(4.5% total FE , 1-0-1 NPK) to promote darker green leaves because of the intense light exposure of my plants.

Special Growing Techniques

I am grateful to have people such as Jerry Meislik and Suthin Sukoslovisit as well as internet web resources to get ideas on ways to promote greater growth rates and to re-style trees.

I am wrapping and packing aerial roots to fuse/self graft a trunk or to fuse roots together.

F.microcarpa with aerial root in milk container full of soil to encourage their growth, height 30", width 38".


Same tree with new aerial root on right but not long enough to enter the soil.


Aerial now covered with soil and plastic wrap until it grows into the soil.


Over the years I have reduced the height of some on larger trees from almost 40 to 29 inches, helping to make the trunk look larger.

F.microcarpa 1995, height 42x32".


Same tree some years later.


Same tree being developed to have a wider and shorter canopy, 2009, height 27-8x 40" width.


Another example of height reduction below.

F.microcarpa in 2003, height 28".

Same tree in 2009 reduced back to main limbs, height, height 19". Pot Tokoname 22x16x3.5" .


Same tree in 2009 showing vigorous re-growth.


I use a space heater next to a patio block with trees on top of it to generate bottom heat to warm the soil in the winter to push growth. It does if you are willing to water 4-5 times a day for a small tree. One Bougainvillea pre-bonsai I have had 6 non-lignified branches near trunk base go from about 10 inches to 40 inches in two months coupled with heavy feeding and bright light.                                  

My Goals For Bonsai

I prefer my trees to look naturalistic as opposed to looking like a conifer or a traditional pine tree style. Since Ficus is my favorite tree I often see this species styled somewhat like a pine with heavy primary branch pads obscuring secondary branching. I believe a naturalistic style has more tension and negative space hopefully without provoking chaos.

I also strive for some movement in my trees. This could include heavy primary branches moving up-down-then up; trees taking a direction ie. left-to-right; slanting or reclining. Banyans and groves can even create some tension by taking a direction.

I have as a goal to make some of my trees go beyond bonsai styling and try to evoke a feeling of calmness, loneliness, simplicity, or antiquity.

My goal with shohin trees would be to generate more negative space and to have viewers moved beyond responding "What a base or That's so cute!"                                                                                                                                                                                                   

F.salicaria, reduced back to primary branches, 1999.


Shohin F.salicaria developed from above, 2009, height 9", width13". Pot 10x7.5x3".

Shohin F.salicaria defoliated, 2009.

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