Larches as Bonsai

By Rachel Seville

Introduction 

Larches are a deciduous conifer.  They are an alpine tree growing in the cooler regions of the northern hemisphere.  Their natural growth produces a slender, upright tree with a conical shape and drooping branches. 

There are two types of larch primarily used in bonsai – the European larch (larix decidua) and the Japanese larch (larix leptolepsis).  Other varieties include larix laricina and larix x eurolepsis.  It should be noted, however, that the Golden larch (pseudolarix amabilis) is not an actual larch and its care regimen as a bonsai is more similar to that of a spruce or cedar. 

The European larch is native to central and southern Europe.  It has straw-coloured branches and greyish bark which can form interesting cracks and ridges.  The Japanese larch is native to Japan and has reddish-coloured branches. Needles are more tightly clustered in smaller bundles relative to the European larch. 

Larches are tolerant of full sun in the spring and autumn but require partial shade from the hottest days in summer.  Larches do not like humidity.  They also require a lot of water.  Ideally, they should be watered when the soil is still slightly damp.  They should not become saturated but they should not be allowed to dry out completely either. 

Larches as bonsai have many advantages.  As a native species, they are suited to the climate and are resistant to pests and diseases.  They are hardy, tough, adaptable trees suited to a wide range of styles and sizes.  They offer spectacular bright green foliage in the spring and summer, a superb golden colour in the autumn and an excellent winter silhouette. 

Spring

Repotting * Roots * Soil Mixes * Fertilisers 

Spring is the ideal time to repot larches. There is an optimal point when the buds begin to swell and turn golden and the tiniest specks of green appear.  Once green foliage has appeared, it is too late.  Repotting will weaken the tree.  Larch roots can appear to be rotten in winter and early spring.  It is important not to cut away too many looking for better ones.  Inside the mushy brown exterior is a fine, white filament which is a healthy root.   

A good soil mix to use for larches is one part akadama, one part lava rock and one part pumice.  Akadama holds moisture and retains fertiliser.  Lava rock provides excellent drainage and aeration.  Pumice provides excellent drainage and holds moisture.  All these soil components are inorganic which means that the tree will need additional fertilisers and tonics. 

Fertilisers contain nitrogen, phosphorus and potassium which are shown as an NPK value.  Nitrogen is the key component which contributes to growth.  A high nitrogen feed would have an N value above 10.  A medium nitrogen feed would have a value between 1 and 10.  Which to use depends on the stage of development of the tree.  If the tree is in development, a high nitrogen feed will help it to grow and fill out.  If the tree is in refinement, a medium nitrogen feed will maintain steady growth without it becoming too bushy which is particularly important with European larches.  Seaweed is a tonic or growth stimulant rather than a fertiliser.  It can be used in addition to a fertiliser to keep the tree in optimal good health. 

Summer

Auxin * Cytokinin * Pruning * Ramification 

Auxin is a hormone found in the shoots of all plants including trees.  It tells trees to grow outwards and upwards towards the light.  The highest concentration of auxin is found in terminal shoots.  When these shoots elongate, auxin is transported down through the tree towards the roots.  Cytokinin is also a hormone produced in the root system of all plants including trees. When shoots elongate, cytokinin is transported up through the tree towards the terminal shoots.  Auxin and cytokinin interact in a process called crosstalk.  This process must be allowed to occur in order for the tree to produce better top growth.  As a result, it is better to just let larches grow in the early spring months. 

However,  leaving the shoots to extend into summer and doing nothing is not an option.  Auxin will by-pass the lateral shoots meaning that ramification will not increase.  Pinching extension growth and removing terminal shoots in the summer months will activate the auxin in the lateral shoots which over time will improve ramification.  Early pinching can take place at the start of June.  Late pinching can take place towards the end of August. 

Larches are an elongating species.  Summer pruning for larches focuses on extension growth.  There will be 2-4 basal buds at the base of each shoot.  Cutting a shoot back almost to the base will activate these buds which will produce secondary shoots.  If filling out an area, such shoots can be allowed to extend.  If not, shoots can be pruned back to two buds.  Leaving one bud will not improve ramification.   

Larches also produce spurs.  These occur on areas that the tree does not want to extend.  Normally, spurs only have one terminal bud.  If this is removed, the spur will die.  However, if there are several buds, these can be thinned out back to two. 

Larches look better if all downward facing needles are removed.  New buds can appear on the top, side or underside of new shoots.  All downward-facing buds should be removed as this stops the branch from becoming too congested.   

Autumn

Wiring * Jin * Shari * Cones 

Autumn is the ideal time to wire larches once the needles have dropped.  Although very pliable, larch needles are also very delicate and can easily be crushed if wiring is attempted when the larch is fully green.  Several applications of wire over many months may be needed before branches fully set.   

Autumn is also a good time to work on deadwood.  Larches can produce spectacular deadwood but as a softwood species, this does need to be protected to prevent it from rotting.  Lime sulphur can be applied to protect the wood and bleach it.  A wood hardener can then be used to further protect the wood.  Wood hardener should be applied after the lime sulphur. 

Larches produce attractive cones which can grow for two years before shedding their seeds.  Such cones require a huge amount of energy from the tree.  For this reason, all cones should be removed on bonsai in development.  If the bonsai is in refinement, two or three cones can be left for aesthetic purposes.   

Winter

Dormancy * Thinning Out 

Although larches are some of the hardiest trees in the world, they must experience a winter dormancy in order to survive.  A continual freezing and thawing of the roots during winter will harm them and it is better that they remain frozen.  If winter dormancy is broken too early, larches will bud too early.  Over time, this will weaken the tree and may even lead to sudden death syndrome. 

Years of pruning back extension growth on larches will produce bud clusters.  These are the basal buds of pruned shoot stubs and can have as many as twenty buds on them.  These can make branches look ugly in winter and cause foliage to become too tights and distorted.  It is therefore important to thin out these clusters.  This can be done by working out which buds are grouped on the same shoot stub.  Selected stubs can be cut away leaving just one.  Buds on the remaining stub can be thinned out down to two.   

Growing Larches From Seed  

Seeds need to soaked in warm water for 24 hours.  They should then be stored in a refrigerator for approximately 120 days.  Seeds should be kept moist but not soggy.  They can be placed in a sealed container with sphagnum moss or vermiculite.  Soil can be prepared using an equal part mix of potting soil, sand and perlite.  Seeds can be planted in a seed tray about 2mm deep and 2-3cm apart.  The soil should be kept moist but not waterlogged.  They should be kept at a room temperature of 20-25º in plenty of light. Germination usually occurs within a few weeks.