(First published in this format in our 1984-85 Yearbook)

When to Prune


See also Frank Venturella’s “When to do” Plant Calendar for Tucson


        This is the time of year for regrowth, renewal, repotting, and restyling. From the end of February through the beginning of May, most plants can be potted or repotted successfully here.  The frost sensitive specimens can probably wait until after the middle of March when the nightly air temperatures usually do not dip below 50°F. Faster-growing young trees or plants which have been in the same container for two or more years may need to be repotted.  Before this is done, consider if a different size, style or color container will better enhance the appearance of the bonsai.  Perhaps just a slight re-positioning in the existing pot is all that is necessary.  Or a radical restyling may be in order to finally bring out the true spirit of a particular “problem child.”  (Of course, during the winter slowdown you’ve already had time to do this kind of planning . . . )
Ideally, pot / re-pot  just as the new leaf buds are reaching their maximum size before they start to open.  This ensures that there are sufficient internal reserves in the plant to keep it going during the one to two weeks before new feeder roots have developed enough to continue absorbing nutrients for the plant.  If major root pruning was not done at this time, feeder roots will be active much sooner. Try to work in the shade, out of the wind, on a day when the dew point is at least 30° F.  Keep a spray bottle near to moisten the root ball as needed. Use sharp scissors when cutting roots and make clean cuts.  The younger and more vigorous your tree is, the more frequently you might prune roots.  Remove the tap and other large roots with concave cutters.  Be sure not to try to cut rocks or anything other than roots!  The top growth of your tree is, to an extent, a reflection of the bottom growth, and vice versa.  By keeping the roots fibrous and well balanced, the top growth will follow suit. Fertilizer primary components of N itrogen – P hosphorus – Potassium ( K ) are necessary, respectively, for Leaves & Stems – Roots & Flowers – Overall Health and Hardiness.  At least fifteen other elements in smaller quantities are also vital for the life of plants.  Organic fertilizer is not necessarily “better,” but it can provide helpful small amounts of more complex substances which the inorganic commercial blends don’t include.  It is wise to alternate between the two types. In the repotting mixture you may want to include about a quarter-label-strength application of slow release solid fertilizer with micronutrients.  This could be either as Osmocote ® granules or Gro-Power ® planting tablets. Have the roots not grown very much since the last time you potted?  Consider your choices: use a coarser soil mix this time; make sure your pot drains better; decrease the nitrogen and/or increase the phosphate content of the fertilizer for this tree; do not disturb the roots for a few years. Leave the plant out of direct sun or wind for a week, and gradually reintroduce it.  Initially cut back somewhat on the amount of water you give it.  Use the transition period to also spruce up your personal display area.  Even if you never have visitors over, your trees deserve to be shown off in the best possible way.  After a few weeks, begin adding some balanced organic fertilizer.  Junipers and pines will benefit from weekly foliar feedings of fish emulsion.  Finally, cut off any flowers just as they finish blooming to ensure the next year’s good showing. Unless you specifically want to bulk up a trunk or branch, do not let the new side buds and branches grow too long.  Cut back and limit the active buds to only a pair or two per branchlet.  The goal is to have compact, ramifying growth.  Elms and junipers may require weekly “haircuts.”  Clean and oil your tools after each session.



— long, hot, and dry — in Maricopa County presents unique challenges to bonsai enthusiasts. Keeping in mind the variations due to each tree’s size, variety, age, health, and microclimate positioning, the following are tips to help your bonsai survive   and FAQ: Summer Care ) : Grow native or naturalized plants. Use the recommended coarse soil mix. Keep your plants healthy and pest-free.  Rotate each plant a quarter turn every week.  This gives even exposure to the sun and fresh air, plus allows you to check on the health or dis-ease from all sides. Don’t let your plants get out of control, especially the faster growers like junipers and elms. Keep new growth pinched after it gets only so long.  Don’t lose the shape you’ve spent time working on.  Thin any tight growth to allow air and light flow. Be aware of the water-retention of each pot of soil mix.  Slight differences in soil materials when each plant was potted up, the requirements of each type of tree, the siting of each pot — all these prohibit a “one-method-fits-all” watering.  Learn to customize to your plants’ needs. Provide shade cloth overhead, especially after noon.  Or site your bonsai under landscape trees or shrubs. Set pots on low stands or slatted workbenches over a lawn, mulch or gravel; less preferable is over concrete or desert landscaping.  Soak the ground thoroughly in the morning.  Give the trees an occasional good-strength shower. Over-pot your trees in the springtime.  The extra room will be much appreciated.  Or, sink your potted trees in a layer of mulch or sawdust.  Check every now and then that the roots haven’t grown out the drainage holes and into the ground! Set pots near a swimming pool or pond, or above but not in pans of water.  Be aware of reflected sunlight. (Keep trees a little way away from south or west facing masonry walls or windows.) Group plants together, but not touching one another.  Allow room for good air circulation. Don’t let your more delicate trees get unfiltered west/afternoon sun or a monsoon dust storm. Have your plants spend the summer in a growing bed, not in their pots.  Prune vigorous top growth. Water maples and other plants bearing thin-edged leaves with distilled or reverse-osmosis (RO) water.  Remember to fertilize half-strength regularly. If a bonsai has wilted leaves, put it in the shade and give it a little water.  Give it a little more water later that day.  Let the roots recover slowly — don’t drown them. When established — not recently repotted or root-pruned — larger specimens of the following can take full sun:  bougainvillea, elephant food, fruitless olive, lantana, lysiloma, Texas ebony, junipers, dwarf myrtle. In the late summer and throughout the fall use a high phosphate fertilizer, such as a 10-60-10 blend, for the flowering trees.  This allows the plant to build up reserves and rudimentary buds for next spring. Sketch or photograph your trees.  Determine what kind of tree would be right — or wrong — for that empty container you have.  When traveling, study full-grown trees.  Notice their shapes: what is it that gives them “character?”


The second growing season of the year has begun, running from mid-August through mid-November. Again, don’t let your plants get out of control, particularly the faster growers like junipers, elms, and pomegranates.  Keep new growth pinched after it gets only so long. We cannot stress this enough: Be aware of the water-retention of each pot of soil mix.
Don’t let your more delicate trees get unfiltered west/afternoon sun.  Autumn still means “hot and sunny” here.
Give a high phosphate fertilizer, such as a 10-60-10 blend, to your post-bloom flowering trees to build up reserves and rudimentary buds for next spring.  This is also recommended for pines and junipers now.  These latter two kinds of plants also can be best wired in the Autumn and the wire left on — with constant visual checking for too-quick growth that might scar — until the following Autumn.



in Maricopa County is generally mild and can be somewhat dry. As a worst case scenario, near Central Phoenix we might see one or two nights with a hard freeze  — air temperatures below 32°F for several hours in a row.  Heading outward from downtown, that total might increase to seven or ten nights.  Most of these are conveniently and accurately predicted by the TV or  other weather forecasters . In the event of a hard freeze in your area, frost-tender bonsai such as bougainvillea, elephant’s food, the various Ficus, lantana, natal plum, and so forth need extra protection.  (See Plants for Bonsai for a complete listing.)  If you can, before sunset move the trees close to the house and under a porch or the edge of the roof so that vertical air drafts will not directly reach them.  Elevate the pots on concrete blocks or a table or bench and put a section of newspaper directly under each pot to provide a layer of insulation.  If winds or breezes are likely, drape a newspaper page over each pot, anchoring it under the corners of the pot.  Do not use plastic sheeting. An unheated but protected room, garage, or storage closet can also be used.  Again, place an insulative layer of newspaper below the pots. If you notice or suspect frost damage to your bonsai, it is best to wait until the appearance of new growth before trimming any branches.  Plants will always surprise you with their hardiness. Be sure to keep an eye on the water needs of each tree.  Watering can generally be done less frequently now.  But do pay attention to the dew point: a few days in the winter here can have very, very low dewpoints.  At those times moisture is easily lost from even leafless trees. DO NOT fertilize in the winter.  Wait until the appearance of swelling leaf buds before feeding any tree. Take time now to clean and oil your tools, clean your empty pots, review your books and magazines.