Pruning

Pruning pine bonsai is dependent on the species.  There are two broad categories of pine bonsai: single-flush and double-flush.  Single-flush pines are those that produce one flush of new candle growth each year in Spring.  Double-flush pines are those that can be induced to produce a second flush of growth in mid-summer through the process of decandling, also known as mekiri in Japanese.

For single-flush pine bonsai, allow the new candles to emerge in Spring through to early Summer.  As the white sheaths at the base of each new needle begin to naturally shed (typically by early to mid-June in the northern hemisphere), cut back each candle to an even length across the entire bonsai.  Be sure, though, to leave some of the new needles from this year on each candle, as removing the entire candle can cause the branch to die back.  Native US pines that fall into this category include: Ponderosa Pine, Virginia Pine, Lodgepole Pine and Limber Pine.

For double-flush pine bonsai, allow the new candles to emerge in Spring through to early Summer.  In June to early July, completely remove the strong and medium-strength candles back to last year’s needles.  This will induce the production of a new set of candles from each cut site.  By performing mekiri, or decandling, it is possible to produce twice as much branch ramification and shorter needles in one growing season.  The Pitch Pine is the only native US species that falls into this category.

Heavy pruning on all native US pine species is best done in the late Summer through Fall, from late August through October.  By pruning unnecessary branches and plucking old needles at this time of year, it is possible to induce back-budding, or adventitious buds, on pine bonsai.

For a more in-depth look at pruning techniques, please consider joining our online bonsai learning platform Bonsai-U!

Wiring and Styling

Wiring and styling pine bonsai is best performed in the late Summer through Fall.  During this period, back-budding can be induced by bending and shaping the branches.  Avoid wiring and styling pine bonsai in the Spring through the Summer, as this is when the new buds and candles are forming, which can easily be damaged.

Repotting

Repotting pine bonsai is best done in Spring just as the buds begin to swell.  This usually happens sometime in March in the northern hemisphere.  When repotting, do not remove all of the original soil, but rather leave a core of older soil beneath the trunk to preserve the health of the bonsai.  Avoid cutting too many roots as well, as this can weaken the pine bonsai in the subsequent growing season.

Use a free-draining soil medium, such as Aoki Blend or a mixture of akadama, lava rock and pumice in a ratio of 1:1:1.  The soil particle size should be approximately 3/16 inch (4mm) for medium and large trees, and slightly small for shohin size bonsai.

Watering

The watering needs of pine bonsai will vary from species to species.  However, as a general guideline, check the water twice per day during the growing season from early Spring through late Fall.  Most pine bonsai will need to be watered at least once per day, and sometimes twice per day, during this period.  Water as the soil surface becomes dry.  In the winter months, check once per day and water as needed, which could be as little as once every 3-5 days depending on the climate and the individual pine bonsai.

Fertilization

For young single-flush pine bonsai, fertilize from early Spring through late Fall using an organic fertilizer cake, such as Biogold or Tamahi.  This might cause the needles to elongate; however, the goal with a young bonsai is to produce rapid growth and thickening.  The needle size can be reduced at a later time.

For older, refined single-flush pine bonsai, do not fertilize until the new growth has completely hardened off.  This typically occurs in mid to late Summer.  At that time, begin fertilizing with the same organic fertilizer through late Fall.

In regards to double-flush pine bonsai, begin fertilizing with an organic fertilizer cake in early spring to increase the vigor and health of the first set of candle growth.  When that growth is then decandled in June, remove the fertilizer and do not apply new fertilizer until the second flush of growth hardens off in early Fall.  This will prevent the second flush from growing too large and long.

Placement

Place pine bonsai in full sun year-round.  If you live in a hot climate, however, make sure to protect high-elevation pine species from the heat by placing them in afternoon shade.  For example, Limber Pine and Ponderosa Pine are best protected from the hot afternoon sun, while Pitch Pine and Virginia Pine can stay in full sun all day.

Pests/Diseases

Pine bonsai are susceptible to a number of pests including aphids, borers, caterpillars, mealybugs and weevils.  The most common diseases that affect pines are tip blight, needlecast and rust.  For a comprehensive understanding of what fungicides and pesticides to use on your pine bonsai, please join Bonsai-U!