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Columbus Ohio Bonsai Care Calendar

The Columbus Bonsai Society
USDA Hardiness Zones 5-6 (5 Northern Ohio, 6 Southern Ohio)

Numerous bonsai enthusiasts have contributed to this article with experience in Central Ohio.
When reading about bonsai care, it is important to know where the author lives and has experience.
These tips are mainly for deciduous, pines and junipers.  While tropical trees have semi-dormant periods, they may be repotted, pruned and fertilized year round.  Keep in mind that each species has its own timeline and may not follow the exact timing shown in this article.  Also, know that weather and seasons vary each year, so keep an eye on the forecast and always protect your trees from weather that is out of the ordinary.
You may not always have the time to work on your trees during the “right season”.  If the health of your tree is at stake, you should ignore these suggestions and take the appropriate action immediately.  Sometimes it may be necessary to repot your tree or slow its watering in summer.  If you have questions, feel free to contact us, providing as much information as possible, and we will do our best to help you.

Month - Season - Average High / Average Low

January - Mid Winter - 36/20

  • Only water when soil is almost dry.  Soil may stay damp for many weeks without the need for water.
  • Heavy pruning of deciduous trees can be completed in winter, while the tree is dormant.  It may be best to wait until early spring, when dead branches from winter are more noticeable.
  • Start deciding which trees will be repotted in spring.  Make a list of available pots, and which trees will work with them.  Having a battle plan is very useful once the chaos of spring arrives.  Order repotting supplies such as new pots, soil, wire, drainage mesh, etc.
  • Protect your trees from direct winter sun and wind as it will cause freeze dry damage.
  • You may place mothballs in the mulch around your trees to prevent mouse damage.
  • Extra mulch or protection is needed if the temps fall below 20, especially for elms, maples and other fleshy rooted plants.

February - Late Winter - 39/22

  • Wire conifers now through early summer.
  • This is the best month for repotting conifers.
  • Use a dormant pest spray to keep pests away in early spring.
  • All tips from January apply in February.

March - Early Spring - 50/31

  • Repot deciduous trees if their buds are starting to swell.  If you wait until the leaves have emerged, you will need to take more care to keep the tree out of direct sunlight and wind.
  • Be sure to check wire from last year.  The spring's growth will cause tight wire to cut into the tree.  Remove any that is tight.  This should be done year round as well.  If the branch did not hold its shape, reapply wire.
  • You can wire branches on all trees, but be careful of buds and swelling branches caused by growth.
  • Grafting is possible on most trees now through spring.
  • You may bring hardy trees out of winter protection now, as most can handle temperature above 20°F. 
  • This is an ideal time to take hardwood cuttings from deciduous trees.

April - Mid Spring - 62/40

  • This month, most deciduous will have buds swelling and leaves emerging.  Be ready to repot if needed.
  • Repot pines and juniper this month, after the candles (pine buds) begin to swell.(
  • Start balanced fertilization as new growth begins.  Continue fertilization until mid summer.
  • Spray to control pests that feed on fresh, early growth.
  • This is a good month to take pine and juniper cuttings.
  • Allow new deciduous growth to extend to 3 leaves or leaf pairs, and then cut back to 1-2 leaves or leaf pairs.  Continue through summer.
  • Most non-tropical trees should be outdoors by the end of April.
  • BEWARE:  There always seems to be a late frost from April-May.  Watch for frost advisories and protect your trees by bringing them into a garage, basement, or by using a cloth netting.  All new growth is susceptible to frost damage.

May - Late Spring - 73/50

  • Start hardening up indoor tree growth by using an oscillating fan a few hours a day.
  • You should move tropicals outdoors now.  Introduce tropicals to the sunlight gradually.  Be careful of night time temperatures <45°F.  You may also leave tropicals indoors year round, but most will benefit from the outdoors.
  • Most deciduous trees have the leaves out sometime in May.
  • Holding back fertilizer for pines can keep their needles shorter.
  • Perform air-layers on trees once their leaves are fully emerged.
  • Start fertilizing with a balanced 10-10-10 or 20-20-20 fertilizer for most trees.
  • Trees will be using more water now that they are actively growing.
  • Re-pot any later emerging species, and any that show signs of being pot bound – they won't make it through July and August if you don't.
  • Pinch or cut back long pine candles to encourage back budding and a more dense overall growth

June - Early Summer - 82/59

  • This is a good month to air layer trees.
  • After you remove dead flowers, Rhododendron and Azalea are ready for pruning.
  • Wiring stiff deciduous is easier now that sap is flowing.  Foliage makes this task more difficult though.
  • Continue pruning deciduous and tropicals for shape and to force growth that is more compact.
  • All trees will be in full growth mode, so water usage is significantly increased.
  • White or 5-Needle Pines:  Cut stronger/top candles first, then lower/weaker candles a few weeks later.
  • Black or 2-Needle Pines:  Cut weak/lower candles first, then strong/top candles a few weeks later. 
  • You may completely defoliate strong and healthy deciduous trees to produce smaller foliage and ramification.  Do not wait any later than June, or the tree’s new growth may not harden up enough in time for winter.  This technique should not be completed in successive years, as it is stressful on the tree.  This technique is usually reserved for maples.

July - Mid Summer - 85/64

  • This is the hottest time of year, so most trees need water every day.  Water in the morning, the evening, or both.  Watering in the evening may increase the risk of fungus.  Some trees’ roots will not take up water in the extreme heat.  If your root ball remains wet in hot temperatures, do not re-water.  You may want to repot this tree next season.
  • Remove old needles on pines.  They should be discolored and useless now. 
  • Creating Jin and Shari is easier in the summer due to sap flow. Removing bark from live branches is easiest when restyling and difficult from truly dead wood.
  • Protect trees with delicate foliage, from the sun, such as Japanese maple.  This applies through the summer season.
  • Tropical trees should be in the peak of their growth.  Hard pruning can occur now on tropicals.
  • Summer repotting should not be done, but if it is necessary, disturb roots as little as possible.  Transplant these trees either into the ground or into a larger pot with more soil.

August - Late Summer - 84/62

  • Continue pruning, but watch for buds and think about next year's growth.
  • Use lime-sulfur on jin and deadwood in summer.  The heat and sun helps it absorb into the wood, and the sunlight bleaches it quickly.
  • Most deciduous and pines have a semi-dormant period in the extreme heat of summer.  Be cautious of watering.
  • August-September is the ideal time for repotting tropical trees.
  • You may start lowering the Nitrogen content of your fertilizer to slow foliar growth in preparation for fall and winter.

September - Early Autumn - 77/54

  • This is an ideal time to start root over rock plantings and other root development projects.  The tree is starting to concentrate growth in the roots and use less energy on the foliage.
  • Lower the nitrogen content of your fertilizer this month.  Switch to a 0-10-10 fertilizer. The lack of nitrogen slows foliar growth, which will force the branches to toughen up to deal with winter's wrath.
  • This is the second best time for repotting.  Once the leaves turn color, the tree is dormant.  You may transplant deciduous after this.  This is better done in the beginning of the month.
  • This is a good time to collect wild trees.
  • Bring tropicals back indoors towards the end of the month, or when temperatures consistently drop below 50°F at night.
  • Spray your tropicals with pesticide before you bring them indoors.  This may take multiple applications over a few weeks.
  • Watch out for fall pests.  Squirrels are especially harmful, as they are digging and foraging for winter.

October - Mid Autumn - 65/43

  • Trees will be using much less water now that the foliage is going dormant.  Do not water unless needed.
  • Try not to prune deciduous in the fall as it may force new growth that will not survive winter.  Wait until the tree is fully dormant.
  • Prepare your winter storage area now, before winter sets in.

November - Late Autumn - 51/34

  • Stop fertilization for outdoors trees.
  • Only water when soil is nearly dry.
  • Clean up trees in preparation for winter.

December - Early Winter - 40/25

  • You may wire trees, as their lack of leaves makes it easier this time of year.
  • Move your less hardy and smaller trees into a protected area.  This may be a cold frame, an unheated garage, a cool basement, or mulched near the side of a building.

Members of the Columbus Bonsai Society
Keeping Your Bonsai Alive and Well - Herb Gustafson
Practical Encyclopedia of Bonsai - Ken Norman
Bonsai Techniques - John Naka

Revised: 6/6/2009