The second critical factor is humidity. Most homes are incredibly dry due to the heating and cooling necessary for human comfort levels. In fact the humidity in our homes is less than the average desert. Plants, excepting cacti, will not grow and flourish in such low humidity. Any technique to humidify the area around the plants will allow better plant growth. Misting and spraying plants frequently helps but is impractical. A humidifier close to the plants may be beneficial. Last, surround the growing areas with a plastic "tent" and increase the humidity around the plants, but don't completely seal plants in plastic since fungus will take over.
Temperature is another important factor in plant growth. In general most plants thrive indoors in a range of 60 to 90 degrees Fahrenheit. Higher or lower temperatures will result in slower growth of some plants or even their death. Varying temperatures from a daytime high and cooling down twenty degrees at night allows materials considered difficult to be grown indoors.
In twenty three years I have culled through plants searching for plants that will tolerate indoor conditions. Some species have been failures and others have been very successful. Following is a list of ten plant species that I have found to be suitable for indoor bonsai and suggestions to allow success with these plants.
Common Name - Scientific Name
1. Chinese Banyan - Ficus microcarpa Click here to view image.
Many varieties available.
Leaves dwarf well in pot culture.
Tolerates heat and dry air.
Excellent root flare and buttress development.
Tolerates pruning well.
Easily grown from cuttings, and air layers.
Aerial roots develop in humid, dark conditions.
Less useful for small (Shohin) bonsai.
Water and fertilize regularly.
Give as much light as possible.
Keep evenly moist.
Avoid temperature below 50 F.
2. Chinese Sweet plum - Sageretia theezans
Small leaf size.
Exfoliating bark - if over 6 years old.
Tolerant of high heat and light levels.
Easily grown from cuttings.
Difficult to wire old wood.
Collected specimens difficult to re-establish.
One of the few plants that never seems to rest; It is always in active growth.
Appreciates even moisture and frequent fertilization.
3. Buttonwood - Conocarpus erectus - Click here to view image
Gorgeous dead wood on collected specimens.
Leaves dwarf with pot culture.
Not fussy as to soil type.
Must never dry out.
Hard to obtain collected specimens.
Keep warm and never below 50 Fahrenheit- especially roots.
Soil must be kept moist; never allow to dry out.
Avoid the use of pesticides as toxicity is common.
4. Natal Plum - Carissa grandiflora Click here to view image.
Leaves reduce with cultivation. Smaller leaf cultivars available.
Tolerant of heat and dryness.
Flowers and fruit are attractive.
Must have a coarse and well-draining soil.
Older wood is brittle and difficult to wire.
Plants respond to severe pruning (reduction) with new growth.
Blooms on terminals of new growth; limit hard pruning if flowers/fruits are desired.
Grow the plants slightly drier rather than wetter.
Wire branches while green; woody branches will break.
5. Lantana - Lantana camara
Flowers and fruits easily.
Drought resistant and heat tolerant.
Easily grown from cuttings.
White flies love this plant.
Trunk does not fatten readily in pot culture.
Branches are brittle and break easily; if the branch breaks stop immediately and leave wire on until the fracture heals, then cut the wire off.
Yearly repotting is beneficial.
Do not overwater.
6. Pomegranate - Punica granatum
Fruits and flowers.
Dwarf varieties available.
Winter rest is necessary and some chilling is helpful. But definite cold requirement is not necessary.
Allow the plant to go dormant in the fall by keeping the plant cooler and drier. Leaf drop will occur.
Do not fertilize when at rest.
7. Singapore holly - Malpighia coccigera
Flowers well but rarely fruits indoors.
Trunk remains small.
Keep lightly moist and well fertilized.
Appreciates trace elements in soil mix.
8. Olive - Olea europaea
Good bark color and texture.
Excellent trunk buttress.
Tolerates heat and dryness.
Older wood difficult to wire.
Avoid constant soil wetness- prefers to go nearly dry before watering again.
Rests during winter but retains leaves.
Wire branches while green and supple.
9. Parsley aralia - Aralia elegantissima
Brittle branches make wiring difficult.
Roots won't tolerate constant wetness.
Branches irregular and coarse.
Let soil dry between waterings.
Watch for insect infestation.
10. Schefflera - Brassaia actinophylla and Dwarf Schefflera
Tolerates low light.
Tolerates low humidity.
Brassaia tolerates dryness. Dwarf Schefflera must be kept moist.
Will form aerial roots under humid conditions
Large leaf size.
The plant to try if you have killed everything else!
PLANT MATERIALS - ADVANTAGES and DISADVANTAGES
1. Schefflera/ Brassaia 1,2,3, 6
2. Ficus ( Figs) 1,2,3
a. salicaria, salicifolia, nerifolia etc. (Narrow Leaf)
b. benjamina (Weeping fig)
c. microcarpa, retusa (Chinese banyan)
3. Honeysuckle (dwarf)
4. Cotoneaster 2,4, 9
5. Holly (Ilex vomitoria) 4, 6,10
6. Malpighias (punicifolia, coccigera) 2,3,4
7. Sageretia theezans 1,3
8. Cuphea hyssopifolia 4
9. Buttonwood (Conocarpus ) 3,5
10. Serissa foetida 1,4, *Cooler temps may help
11. Citrus sp. 2,3,4, 6,8,9
12. Boxwood (Buxus sp.) 2,6,7,10
13. Pomegranate 1,3,4,6,8
14. Myrtle (Myrtus communis) 1,4
15. Carissa grandiflora 2,3,4, 6
16. Texas ebony 3,6,7
17. Bougainvillea glabra 2,3,4, 6,8,10
18. Crape myrtle 4,8,*
19. Lantana 1,2,3,4,6,8,9,10
20. Olive (Olea europaea) 2,3,6
21. Guava 1,4,5,6
22. Camellia & Gardenia 4,6,9,*
23. Aralia 2,3,6
24. Fukien tea 4
25. Azalea 4,10
26. Junipers *
27. Japanese Black pine 6,8,*
28. Aleppo pine 7
29. Elms (tropical) 1,
30. Jade (Crassula) 2,3,10
31. Hibiscus sp. 1,4,6,10
1. Vigorous grower
2. Tolerates some dryness
3. Tolerates heat
4. Fruits/ flowers
5. Tolerates excess water
6. Stiff or coarse
7. Slow grower
8. High light required
9. Insect susceptible
10. Brittle -caution wiring!
* May require chilling
1. Introduction To Indoor Bonsai, Meislik, J., American Bonsai Society 2006
2. Wonderworld of Tropical Bonsai- Jyotl and Nicunj Parekh
3. Indoor Bonsai- Paul Lesniewicz -Blandford Press
4. Bonsai for Indoors - Brooklyn Botanic Garden Record
5. Growing Bonsai Under Lights - J. Wikle - Light Garden Magazine June 1980