Horticulture Principles and Practices

26.5.2 SANITATION
It is critical to maintain clean surroundings and thereby reduce the chances of disease
and pest attacks. Because of its small size, any disease or pest attack can be devastating
to a bonsai plant. Routine cleaning includes scraping and brushing off moss growth on
the trunk and removing liverworts and other weeds from the soil.
26.5.3 PEST CONTROL
Pests of bonsai include aphids (or greenflies), caterpillars, scale insects, red spider mites,
and ants. Aphids and mites may be controlled by spraying with insecticides. Ants may
attack and destroy roots and should be removed. Caterpillars are readily removed by
hand and destroyed.
26.5.4 DISEASE CONTROL
Powdery mildew is a problem where humid conditions prevail. Rust and black spot may
also occur. Black rot may be controlled by applying sulfur. Root rot may occur if waterlogged
conditions prevail, or if poorly decomposed organic fertilizer is applied. The
bonsai plant should be lifted and all contaminated soil brushed away. Canker is
effectively controlled by cutting away affected plant parts.
26.5.5 SEASONAL MAINTENANCE
Winter
When winter temperatures become severe (below freezing), protection may be required
for outdoor bonsai. Plants may be brought indoors and kept at temperatures below 5°C
(41°F). Fertilization should cease during the dormant period. Water should be provided
as needed but sparingly. Deciduous plants are best pruned in winter, when they shed all
of their leaves. The plants can also be cleaned during winter.
Spring
Outdoor bonsai should be returned to the outside environment only after it is safe to do so
(frost free). Plants begin to bud as active growth resumes. Watering should be increased, but
very carefully. As spring advances, the growth rate increases, and some pruning may be
necessary to prevent excessive growth. When blooms wither, plants should be pruned
before new buds appear. Blooms occur on the previous year’s wood, and any delay in pruning
will prevent blooming in the next year. Coniferous bonsai may be repotted in midspring.
Summer
Foliage growth is intense in early summer. Pinching and pruning are required to control
growth. Water is critical in late summer when it is hot; however, hot and humid conditions
predispose plants to fungal diseases.
Fall
A key activity in fall is to prepare the plant for winter by boosting its nutrition with fertilizers.
Deciduous species display their most intense colors in midfall. Late fall ushers
in the time of leaf drop and the approach of winter. As leaves drop, the plants may be
pruned. Preparations should be made to protect plants in case of an unexpected frost
when bonsai are displayed outdoors.
26.5 Postestablishment Care 719