Care SheetsDeciduous & Cold Weather Bonsai Care Sheet
These are general care guidelines for cold weather and deciduous bonsai. Tree species in this classification include: Pine (Pinus sp.), spruce (Picea sp.), fir (Abies sp.), cedar (Thuja sp.) hemlock (Tsuga sp.), maple (Acer sp.), hornbeam (Carpinus sp.), Cotoneaster (Cotoneaster sp.), birch (Betula sp.), Larch (Larix and Pseudolarix sp.) and Wisteria (Wisteria sp.).
Trees in this climate classification are native to climates which have severe winter seasons. All trees native to the state of Maine would be included in this bonsai climate classification. They have evolved to survive and thrive in these more extreme climates. These are not indoor trees and will die if kept indoors for more than brief periods at a time for display. Never keep a cold climate evergreen or deciduous tree indoors at room temperature for more than 48-72 hours.
Placement and Temperature
During the warm part of the year (early/mid-April to mid-November) these trees should be kept outdoors, as long as temperatures are at 25F or above. In autumn, this will insure that the trees have gone fully dormant before they are brought in to their winter storage area. In spring, this will insure that the trees do not break bud and begin their spring flush of growth too early. Early spring growth can be frost damaged if exposed to temperatures below 32F. If early spring growth is present on the tree, shelter the tree when temperatures are below freezing.
Winter storage locations for cold weather/deciduous trees should be between 20F and 45-50F. This temperature range provides the ideal environment for dormancy. The location should not fluctuate frequently above and below 32F since this will cause repeated freezing and thawing of the roots, soil and inner bark of the tree and can result in damage or death of the tree, particularly maple species. If the winter storage location is always below 45F, light is not necessary for the dormant bonsai and they may be kept in the dark until growth begins in the spring.
Good winter storage locations include unheated basements, unheated sunrooms, garages that have minimal heat, cold frames, cold greenhouses and covered trenches. Even a refrigerator will work. Trees kept in these sheltered locations should be checked for water every 7 to 10 days. Temperate and cold weather trees should be kept moist during winter dormancy. Do not overwater and saturate the soil at this time of year since a waterlogged soil during the cold winter season provides an ideal climate for root rotting organisms.
Species that are winter hardy in your location may also be overwintered outdoors if the following procedures are followed. Overwinter the tree in a location that receives no direct winter sun (the north side of a building, under/behind evergreen foundation plants or under an evergreen tree. In mid-November (before the soil freezes), dig a hole slightly larger and deeper than the size of the bonsai pot, place the tree in the hole and mulch the area, bringing the mulch to approximately 1 inch over the top of the pot and soil. Sawdust or bark mulch are generally used with good results. Water the tree after mulching to settle the mulch around the pot and to provide a final watering before winter. No additional maintenance is required until spring. Once the soil and mulch thaws the tree can be moved to its warm weather location.
Repotting
Cold weather and deciduous trees should be repotted and root pruned in early spring, before the buds swell and growth begins. Follow normal bonsai watering and fertilizing guidelines during the growing season and you will have a long lived, thriving bonsai speciman.
Many new bonsai growers are hesitant to begin growing cold weather and deciduous trees because of the dormant period required. In my opinion they are the easier class of bonsai trees to grow if you live in a four season climate. These bonsai spend most of the year outdoors and only need minimal protection during winter to protect the tree from extreme cold.
Pruning and Pinching
To maintain dense, full growth, pinch off the terminal buds when the new growth reaches 1/2 to 1 inch. This technique will force more side branches to develop, forming dense masses of foliage. Pinching may need to be done several times during the growing season to maintain and develop the desired canopy density.
Pruning is the cutting or removal of unwanted twigs or branches to maintain the desired growth habit of you bonsai. Structural and design pruning and training should be done in early spring when deciduous trees are just beginning to break dormancy. Cold weather evergreen species should have this training done before they begin to flush out new growth in mid-spring. Pruning shears or scissors may be used to prune you tree. Remember to leave a clean cut when pruning, this will encourage rapid healing of the pruning cut.
Seasonal Care
SPRING
To start forcing growth early in the season, we remove the tree from its winter storage to a cool, well lighted place out of direct sunlight. Find a spot where night temperatures are cooler than day temperatures (35-40F night minimum). This method simulates typical spring weather, providing a natural growth cycle and results in healthy, steady new growth. Once the leaves flush out in spring we begin fertilizing with diluted fish or fish/seaweed emulsion once every 2-3 weeks. Otherwise you can just wait until mid-March when the first buds begin showing signs of swelling and move them directly outside once again to grow in tandem with the native trees.
SUMMER
Keep the deciduous trees growing strong by placing it outside in dappled shade. Cold weather evergreens should be grown in full sun to 75% shade depending on the species. Check for water daily especially during hot or windy weather. If you are experiencing a cool, cloudy summer (as we did in Maine in 2000) you will not be watering as frequently and as a result the fertilization schedule can be stretched out to once every 3-4 weeks. During hot dry summers (like the one we had in 1999) you may find that you need to water every day. Remember that frequent watering leaches nutrients from the soil more rapidly, requiring more frequent fertilization of approximately once every 2 weeks.
Keep an eye out for pests and diseases as they are very prevalant this time of year. If you find bugs you may want to check these links~ Insects on the Web or Ecological Garden Projects ~for more information.
AUTUMN
Finish summer fertilization by late August or early September. This will help the plant prepare for the leaf drop ahead. Late season applications of nitrogen can cause late season growth which will not harden off before winter. Applications of rock phosphate or greensand (potassium) can be applied now. These elements will strengthen the root system and aid in flower bud formaton for the following year.
With cooler nights you may find that you don''t need to water quite as frequently. Water only as needed when the soil dries out. Most of all enjoy the wonderful flush of autumn reds, oranges and yellows on deciduous bonsai which make them all the more exciting to grow. Leave the tree outside until it has completely dropped all its leaves.
Before putting your trees away you should scour it again for any signs of pests or diseases. Trees put away with these problems will usually start the new season with these same problems.
WINTER
Once the tree has become fully dormant, with no leaves or new swelling buds, it can be moved into its winter bed. The purpose of this is to ensure that the fragile roots do not suffer winter kill from the extreme cold and second to ensure that the pots don''t expand with the frozen soil and break. See Placement and Temperature above.
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