Elm care
Zelkova parvifolia/Japanese Elms are often sold as indoor bonsai and as such are acclimatised to indoor growing conditions, Japanese Elms sold as outdoor bonsai and all other species of Zelkova should be cultivated outdoors. Japanese Elms grown indoors (or in climates with very mild winters) will remain evergreen where as outdoor cultivation results in a deciduous tree. Ensure indoor trees do not become too cold in their first winter outside. Zelkovas should be able to cope with the adverse growing conditions indoors though they are never as vigorous as their outdoor counterparts.
Very occassionally indoor Elms will still loose their leaves and go into winter dormancy just like their outdoor counterparts. Do not think that the tree is dying. It is just part of the natural process of a tree. As stated this happens very selmdomly to indoor Elms but it can happen nonetheless.
Position
(Indoors) Well lit, cool position on a sunny windowsill during the winter. Keep up humidity levels. Place outside. You tree will also benefit from being placed outside as much as possible from May onwards after last frosts have finished.
When kept indoors through the summer make sure the tree is placed in a bright location but out of direct hot summer sunlight. This will dry the tree out very quickly and scorch the leaves.
(outdoors) Outdoor Zelkovas/acclimatised Zelkovas are hardy to frost though temperatures below -5°C can result in fine branches dying back and root damage so should be afforded some protection. Frost protection can include placement in darkened outhouses and garages as when out of leaf Zelkovas do not require light.
Watering
(indoors) Never allow compost to completely dry out, keep the soil evenly moist. Check the compost daily but only water when necessary. Watering daily as a routine results in sodden compost, leading to lack of vigour, rootrot and eventually death.
(outdoors) As with indoor watering though during periods of strong sun, high temperatures or strong growth in the Spring, trees can need far more frequent watering.
Feeding
(indoors) Balanced feed twice weekly through Spring and Summer. Monthly through the winter. Do not feed when out of leaf.
(outdoors) Once buds open in Spring, feed weekly with high nitrogen for first month then every two weeks until late summer with balanced feed.
Repotting In Spring as buds extend annually until around 10 years old or more and then repot as required. Trees overwintered indoors can be repotted in Autumn when brought indoors after leafdrop. Repot in basic soil mix.
Pruning Allow shoots to extend 3 or 4 nodes then prune back to 1 or 2 leaves as required Larger-leaved Zelkovas respond well to leaf cutting in Summer
Wiring In mid-summer though indoor trees can be wired mid-winter particularly if out of leaf. Care should be taken as bark marks easily.
Propagation Sow seed outdoors in Autumn or Spring. Greenwood cuttings in Summer. Hardwood cuttings in Winter. Air-layering after spring growth has hardened.
Pests and diseases Zelkova bonsai as with all Elm bonsai are not affected by Dutch Elm Disease as the beetle requires the volume of wood only available to it in fully grown mature trees. An attack (if it were to happen) would easily be dealt with by systemic insecticides and fungicides on a potted tree in comparison to the problems associated with eradicating Dutch Elm Disease on a fully-grown tree in the ground.
Watch for aphids, leafhoppers, leafspot and gall mites.
Styling Suitable for all forms and sizes- especially good for the broom form which replicates the natural shape of field-growing Zelkova.
