GROUP IV – Challenging, Difficult to Grow
This Page Last Updated: October 21, 2009
Special Condition Key:

A prefers more acidic soil; try 1 Tablespoon white vinegar in 1 gal. water monthly
B brown leaf tips indicate salt burn/salt build-up, often from too much or too little watering
C subject to iron or manganese chlorosis (best iron source is a chelated mineral)
D subject to random branch die-back (which may be due to wrong-timed pruning)
F frost-sensitive, so protect with frost cloth or bring indoors if a hard freeze is expected
I more adaptable for use as an indoor bonsai than other plants, but still requires a certain level of temperature, light and humidity in order to be healthy and to thrive
L may drop some leaves when relocated or repotted
M very attractive to spider mites, so hose-spray and keep in very good air-flow
P pinch first set of leaves when opened, the next will be smaller in size
R do not root prune if at all possible; never bare root this kind of plant
S leaves sunburn/windburn easily, so provide shelter/protection
U larger specimens can take full sun most of day here when established
W bark is tender or branches are brittle, so wire carefully, if at all, to avoid scars and damage
X Outside of a container, this is considered an invasive plant in some areas: err on the side of caution and discard this plant’s clippings or a “dead” specimen in a trash bag, not just on the ground.
^ evergreen
% deciduous/semi-deciduous
* can bloom as bonsai

Note: Plants labeled as susceptible to chlorosis when grown in the ground should not have this problem in a container with a quality soil mix and regular fertilizer schedule. “Established” plants are firmly rooted and producing a good growth of new buds which have opened up into leaves.


Trident Maple (Acer buergeranum) B,F,S %


        a fast grower that likes water; watch closely if wired to avoid scarring; the leaves grow smaller under more/fuller sun; leaves wilt slightly if dry, but will be O.K. after prompt watering; leaf prune in August and September; the leaves change color in the winter; keep soil moist but not wet in cold weather; soap insecticides are said to be bad for these trees; other dry location recommended species are A. ginnala and A. monspessulanum.     [Aceraceae; Sapindales]     SEE ALSO BCI Plant Sheet.


Japanese Maple (Acer palmatum) A,B,S,W %*


        some leaf burn is inevitable by mid-June; partially defoliate by cutting off a leaf and leaving only the bottom 1/4″ of the petiole after most leaves have turned brown in mid-summer; do not defoliate two years in a row; leaves are more easily burned if the roots are too dry; don’t ever clip healthy (non-burnt) leaves on young/thin-trunked trees or those re-potted this same year or any of the exotic cultivars; don’t healthy leaf-clip even larger trunked trees after mid-June or thereabouts; use low Nitrogen fertilizer, especially after mid-summer; don’t keep soil too wet; needs some winter dormancy; don’t prune heavily after January or so when sap starts to flow too easily; repot every other year; consistency in soil quality and moisture level is said to be more important than protection from sun/wind; ‘atropurpureum’ variety is hardiest here; there are hardier maple species (above); see also Mendocino Maples for info.    [Aceraceae; Sapindales]     SEE ALSO BCI Plant Sheet.


Manzanita (Arcotostaphylos sp.) R ^*


       usually difficult to grow in a container; treat like a cactus: very quick draining soil mix, little water, no fertilizer; buds back on old wood; successfully collecting from the wild said to be next to impossible; some varieties of A. uva ursa (kannicknik) said to be hardiest; per Oracle, AZ grower (2002), dig two weeks after a rain, add mycorrhiza to the soil, use rainwater (!), put moss on soil surface to help maintain moisture level, and spray with water until extra runs out bottom drainage holes.    [Ericaceae; Ericales]


Norfolk Island Pine (Araucaria heterophylla) I ^


      needs bright light; shade small specimens from direct sun; use small specimens for a forest planting; is not a true pine.    [Araucariaceae; Pinales]     SEE ALSO BCI Plant Sheet.


Fairy Duster / Dwarf Powder Puff
(Calliandra eriophylla) F,U,W %*


        said to bloom about three weeks after giving a high Phosphorus (middle number) fertilizer.   [Leguminosae; Fabales]     SEE ALSO BCI Plant Sheet.


Hornbeam (Carpinus sp.)   %


        shade the leaves and keep cool in summer; remove oversize leaves only; allow a small stump to remain when a branch is cut off, the stump will die back.    [Betulaceae; Fagales]     SEE ALSO BCI Plant Sheet.


Japanese Contorted Quince (Chaenomeles lagenaria) B,C %*


        a fast grower; lots of water in well-draining soil mix; prune after leaves drop; needs winter cold for best flowering; leaves open after the flowers do.    [Rosaceae; Rosales]


Buttonwood (Conocarpus erectus) A,F,W


         likes bright light, good air ciculation and consistent moisture; begin with fertilizing one to two weeks prior to repotting in order to fortify the tree for the rigors of the repotting, at the same time prune and wire the tree; repot and root prune in hottest part of summer (at least a month or month and a half more of warm nights and long days with lots of light aids strong root growth), remove twice as much top as root; be careful removing tree from the pot as the weight of soil can break the very fragile roots off at the base of the trunk; Malathion® or Diazinon® will defoliate within one week: if leaves drop, keep caring for — can take quite a while to bounce back; try keeping in a water tray similar to caring for Bald Cypress ; as new leaves develop let them grow out to about five pairs of leaves, then cut off the three end leaves including the apex; never leave the apex on, unless you want the branch to get longer and fatter before developing secondary branches; always prune all branches — any branches left uncut will divert energy from the rest of the tree, thereby growing faster at the expense of the pruned branches; to prune for thicker and more tapered branches, cut all the leaves off and leave the apex on; the rounder the leaf of the specimen, the better the leaf size reduces; to develop more tightly packed leaves cut them severely, cutting the petiole halfway between the branch and the leaf is the most effective method; unless the tree is weak, never leave a portion of the leaves on; do NOT do too much defoliation or branch removal late in the season — a tree that was recently severely worked on is very susceptible to cold damage or death; sometimes these will “pout” in cool winters by wilting: before giving extra water be sure they really do need it; the same trees that “pout” in winter may also “pout” in summer heat; said to do better in winter if pot is positioned on top of a horticultural heating pad or propagation mat; copper wire has possible toxic effects on buttonwoods, especially if it cuts into the bark when left on too long; large trunks and branches will sprout roots if placed in a bucket of water in full sun, somewhere between a few weeks and many months new roots will emerge — even branches broken or cut off and dying trees can be revived this way.    [Combretaceae; Myrtales]


Mexican Heather (Cuphea hyssopifolia) F,I


        NEVER let dry out — the plant will die; requires constant grooming; older plants can be cut back severely in late fall or early spring; easy to grow from cuttings; for compact growth, pinch tips of shoots; do not water for 2 weeks after transplanting / repotting.    [Lythraceae; Myrtales]


Fukien Tea (Ehretia microphylla) F,I,L ^


        slow-growing; give lots of light, but not direct sun; likes heat and humidity, but don’t keep too wet; repot in early to mid-summer; prefers Reverse Osmosis (R.O.) water; needs very good air circulation, otherwise can be attractive to scale insects: fingernail scrape off what scale you can; soap insecticides are said to cause defoliation of these trees, so be careful; said to also shed leaves if overwatered or underwaterd; will die if exposed to slight frost or even a cold draft.     [Boraginaceae; Lamiales]     SEE ALSO BCI Plant Sheet.


Eucalyptus / Gum Tree (Eucalyptus sp.) D,F,R,W ^


        difficult to shape with either wiring or drastic pruning; easily rootbound; neglected nursery stock may be best as these specimens are often ready to be root-pruned and repotted straight away, and their condition might simulate dormancy; tend to experience dormancy in late-summer, as this is often the driest time of year, during this time, there will be no new growth at the tips of branches, and all leaves will have hardened off; it is recommended to remove all foliage from a specimen which is to be repotted; keep uniformly moist and do not let rootball dry out; commonly believed that these should never be repotted deeper than the previous soil level, for fear of the certain death of the tree; generally grow quickly from seed; one or more as yet-unidentified / untried species may do well here; some recommended species are E. camaldulensis (River Red Gum),  E. maculata (Spotted Gum), E. meliodora (Yellow Box), E. nicholii (Willow Leaf Peppermint), E. saligna (Sydney Blue Gum), E. sideroxylon (Pink Flowering Ironbark), and the closely-related Angophora costata(Smooth Barked Apple); see also this thread.    [Myrtaceae; Myrtales]


Ginkgo / Maidenhair Tree (Ginkgo biloba)   %


      only repot every 3 to 4 years; during growing season leaves yellow quickly if light inadequate; in autumn leaves turn yellow and pale before dropping; keep on dry side; leave a stump at base of pruned branch, then remove later when tree has recovered; branches known to dieback if pruned during a hot or cold spell; try making cuttings in October and keep misted.    [Ginkgoceae; Ginkgoales]     SEE ALSO BCI Plant Sheet.


California Juniper  (Juniperus californica) D,M,U ^


       see other junipers; if you get one on a dig, give it plenty of time to re-establish strong growth before you start to prune, a soil heater wire especially during winter can significantly improve the survival and regrowth of a dug specimen, don’t give more than a couple of hours of direct morning sun until it’s putting out lots of new growth,  may need up to a year to reacclimate to full sun exposure, use a very loose soil mix, keep foliage misted and bagged (much moisture is absorbed through the foliage), addition of Superthrive TM  is recommended; will shed about 30% of its foliage during May and June, so better to prune in late summer or early fall.    [Cupressaceae; Pinales]


Crape Myrtle (Lagerstroemia indica) A,B,C,U,W %*


      don’t keep soil too moist; can be heavily pruned just before leaf buds open.    [Lythraceae; Myrtales]     SEE ALSO BCI Plant Sheet.


Australian Tea Tree (Leptospermum scoparium) A,C,R,W ^*


       DO NOT EVER LET THIS PLANT GO DRY, it does not wilt but dies in a matter of hours; water when soil slightly dry on top; style (repotting – pruning – wiring) in stages, not all at once; needs lots of light; don’t prune back to bare wood as it rarely buds back on old wood; try not to bother the roots at all, avoid root pruning as long as possible, do NOT attempt to untangle roots, when root pruning is absolutely necessary shave off a thin slice from the bottom of the rootball and then repot, repeat annually or just continually repot in a larger container; might try sitting pot in dish filled with distilled/Reverse Osmosis (R.O.) water changed regularly, however also said to be subject to root rot; use MirAcid® infrequently and very diluted; less-readily-but-white-flowering L. humifusum said to be much better choice; Australian enthusiasts use some species as very hardy bonsai: what are we doing wrong on this side of the Equator?    [Myrtaceae; Myrtales]     SEE ALSO BCI Plant Sheet.


Japanese Black Pine (Pinus thunbergii) B,R ^


        give abundant organic fertilizer in the spring and summer, including foliar feedings; requires much light; repot young specimens every two or three years, older specimens every seven to ten years; best time to repot here is Feb 15th thru about March 5th (more experienced enthusiasts might be able to extend this range until the end of March); learn about proper candle and needle pinching before attempting to do so; leave all growth on an immature tree through the summer, then cut long growth off in October, repeat this several years until the trunk and branches are large enough, then start trimming candles and long growth in April/May to push out a second smaller set of needles in a single year; mist the needle ends with cold water right after cutting them to slow non-salt browning of ends; needle reduction can be achieved by reducing the amount of water given to the tree in the spring and by regulating the flow of energy throughout the growing season; prefers neutral to slightly acidic soil; California soil mix: 1/3 hard Akadama, 1/3 lava, 1/3 pumice with 5% decomposed granite and 5% charcoal, all washed and screened down to 1/4 inch; another recommended formula is 4 parts chicken grit, 1 part lava rock, and 1 part Black Gold® Cactus Mix; do not overwater, especially in spring and summer — allow soil to ALMOST dry out in between waterings, and then thoroughly rewater.     [Pinaceae; Pinales]     SEE ALSO BCI Plant Sheet.


Purple-leaf Plum (Prunus cerasifera‘Atropurpurea’)   %*


        most Prunus (peach, plum, cherry, apricot, almond, etc.) species seem to live for only a few years as bonsai here; possibly deeper pots will help; Prunus are fairly difficult to root from cuttings and need a stronger rooting hormone that most of us can find in the garden shops; this is the hardiest Prunus here; gorgeous in bloom with white petals against a few green leaves before they turn purplish; do NOT use lime sulphur on; susceptible to aphids.    [Rosaceae; Rosales]


Japanese Flowering Plum (Prunus mume) S %*


        leaves burn easily; cut back on water if leaves have dropped; it is suggested to develop the top first with the plant overpotted, then reduce roots last; flowers between January and March; prune back leaving several buds after flowering to enhance the tree’s design; do not prune the tree again until after the winter bloom; wiring should be done in the spring as required; a sustained feeding program will help the tree to tolerate summer heat and Sahara-like winds: shade and wind shielding during these periods will mitigate leaf damage; however, the tree can  be completely defoliated in mid-to-late spring; do NOT use lime sulphur on; new growth lignifies quickly, so wire new growth soon after it emerges, and then monitor the wire on young growth because it will quickly scar; leaf spot fungus is most easily treated by simply pinching away the diseased leaves; to mitigate fungal problems, do not water the foliage on a daily basis; aggressively feed this tree until the design object is achieved by applying high Nitrogen fertilizers, such as a 20-20-20 NPK, and prune aggressively to promote ramification development, once this is achieved, back off on the aggressive or superfeeding to promote flower bud development; blooms on the prior year’s wood, that is, the buds develop during the growing season of the year before.  When pruning, do not remove all the flower buds; best time to modestly prune is just after the winter flowering; a little more info is here.    [Rosaceae; Rosales]


Pyracantha / Firethorn (Pyracantha sp.)  M,R,U ^*


        surprisingly rated as a “4”, does much better as a landscape plant here than containerized; repot with some of its original soil, best time possibly January here.    [Rosaceae; Rosales]


Serissa / Snow Rose (Serissa foetida) A,F,I,L,M,R ^*


        likes humidity of 65%+, but don’t overwater; wait to water until one leaf turns yellow or dull; signs of overwatering include a sudden loss of leaves, wilting leaves and flowers, and lack of growth; over-watering rescue could take place by putting damaged tree in a nursery container with 50% grit, 30% Perlite, and 20% compost, watering and then putting in a corner: good results should start in a couple of weeks if the tree is not dead; high humidity when flowering said to discolor petals; indoors keep cool; give as much light as possible, but not too much direct sun; similar care and feeding as African violets; can be difficult to shape; remove suckers from base, or train them as smaller members of a grove planting; bugs can become a major problem without excellent air circulation around; leaves turn black and fall off with stunted growth if winter temps go below 55° F; strong Nitrogren fertilizer said to cause black leaves also; very prone to drop leaves when stressed, including getting a change in lighting or temperature; continuous pruning seems to weaken the plant; similarly, only allow one flowering per year and remove emerging blossoms after first flowering is past; wire before watering; wire marks said to grow/fill out O.K.; will bud back on old wood; hold off root pruning as long as possible (and then be aware that cut roots normally emit a rank odor), repot into a larger container if necessary; if tree drops its leaves in autumn or winter, cut back watering and carefully continue limited watering — has been known to bud again as late as May and be healthy; softwood cuttings said to root easily in spring or summer.    [Rubiaceae; Gentianales]     SEE ALSO BCI Plant Sheet.


Bald Cypress (Taxodium distichum) A %


      a fast grower; keep very moist in a good draining soil mix; can even sit in tray of non-tap water if it is changed every other to every few days — no problem in the quickly evaporative summer, just be sure to keep the tray filled then; if it goes a day or two without water and the green feathery branches wilt, fill tray with non-tap water and care for as usual, new growth should pop out within a week from the base of old leaf which has turned black and dead; can be kept a little drier in winter; prefers a deeper pot; unlike with most other plants, to develop branches on these do not allow long growth on them; continually pinch new growth with fingertips before it hardens; immediately remove any buds breaking at the base of branches; buds back on old wood.    [Taxodiaceae; Pinales]     SEE ALSO BCI Plant Sheet.


Zelkova / Japanese Gray-Bark Elm (Zelkova serrata S %


Wisteria (Wisteria sp.)  C %*


        the Japanese species has 15-19 leaflets, and likes full sun; the Chinese species has 7-13 leaflets, and needs some shade; both kinds prefer a high Phosphorus fertilizer in the autumn and also some fish emulsion or rape seed fertilizer; do not use Nitrogen fertilizer after September; have fast growing roots; stop all fertilizing when the flowering begins; cut off dead blooms right after flowering and repot at that time; prefer a deeper pot; trunk wood has to be at least ten years old before the plant will flower; blooms develop out of the previous year’s growth; keep on the dry side in the winter; needs repeated wirings; a New Orleans grower (2001) is said to be successful with pure manure as a potting soil — that’s probably too “hot” for Phoenix — but perhaps you can cut with at least three or four parts of chicken grit to make a workable mix for here; said that sitting in a dish of water in the summer will stimulate flowering; flower buds will drop if the roots are too dry.  See also this.   [Leguminosae; Fabales]     SEE ALSO BCI Plant Sheet.


        treat similarly as you would a Chinese elm, but this species is less forgiving; may be the last type of plant to bud out in the spring, so don’t give up; when trimming the fine branches at the end of limbs, trim the end of each limb or branch as a unit so that the outline of the tree is not smooth but consists of many small sections of foliage that are smooth locally.    [Ulmaceae; Rosales]     SEE ALSO BCI Plant Sheet.



Please be aware that the following plants are no longer specifically listed above
as these have been determined to be too labor-intensive to be properly grown as outdoor bonsai here in the Phoenix area.
Many of these were already considered borderline or had very little experience in our previous listing:

Silk Tree / Mimosa (Albizia julibrissin)
Bottle Tree (Brachychiton populneus)
Blue Atlas Cedar (Cedrus altantica ‘Glauca’)
Hinoki Cypress (Chamaecyparis obtusa)
Cotoneaster (Cotoneaster sp.)
Jade Plant (Crassula arborescens)
Blue Spruce (Picea pungens)
Mugho Pine (Pinus mugo)
Japanese White or Five-Needle Pine (Pinus parviflora)
Yew Pine / Buddhist Pine (Podocarpus macrophyllus)
Indian Hawthorne (Raphiolepis indica)
Azalea (Rhododendron sp.)
Yellow Oleander (Thevetia nereifolia)
Viburnum (Viburnum sp.)