Serissa Bonsai Tree Care

Introduction and Taxonomy

Serissa is a genus of flowering plants in the family Rubiaceae, containing only one species, Serissa japonica. It is native to open sub-tropical woodlands and wet meadows in southeast Asia, from India, and China to Japan. It is commonly called snowrose, tree of a thousand stars, or Japanese boxthorn; and was formerly called Serissa foetida. Snowrose and tree of a thousand stars are different cultivars.

It is an evergreen or semi-evergreen shrub with fine oval, shiny green leaves that have an unpleasant smell if bruised. The upright stems branch in all directions and form a wide bushy dome. It is grown for its neat habit, good coverage of branches and long flowering time. It is also valued for its rough, grey trunk which tends to get lighter in colour with age.

Serissa flowers sporadically from early spring to near autumn on current seasons growth. The 4- to 6-lobed flowers are funnel-shaped. They first appear as pink buds but turn to a profusion of white flowers. Fertilising is especially important during the long flowering period.

Many cultivars with double flowers or variegated leaves are also available. 'Pink Snow Rose' has pale pink flowers and leaves edged off-white. Other cultivars include: 'Variegata', 'Variegated Pink', 'Pink Mystic', 'Snowflake', 'Snowleaves', 'Mt. Fuji', 'Kyoto' and 'Sapporo'.

Serissa is not difficult to maintain as bonsai, but is sensitive to environmental changes. It responds adversely by dropping leaves if over-watered, under-watered, if it's too cold, too hot, or even if just moved to a new location. The plant usually grows back to health when put back to better conditions. Buying a good quality tree from a qualified source is important. A LOT of serissa that are imported from China are already fatally infected with a fungus that will kill the tree within a few months. Others are treated with such powerful pesticides (to meet import cleanliness regulations) that they never fully recover or grow properly.

serissa bonsai

serissa flower

Serissa Bonsai Cultivation

Our experience of this species as indoor bonsai has been positive. The most important factor is having the tree in a good quality growing media. When re-potting we have found that removing all of the fibrous soil these trees are imported in is important. makes an excellent growing medium for serissa. Once in good clean soil serissa only need to be re-potted every 3-4 years. It's perfectly normal for the tree to drop most of it's leaves after re-potting. Following re-potting do not fertilise until you see SIGNIFICANT strong new growth.


Serissa Bonsai in Summer

In summer serissa need a lot of bright light. The ideal position for the tree is outdoors in a south facing position in direct sun. However if kept indoors the tree will do best in a bright conservatory or against a south facing window in which situation it will need to be turned every couple of days. Once you find a spot in which your tree is happy leave it there, it's not normal for plants to move around! If you move your tree to a new spot leave it there for 4-6 weeks to acclimatise before deciding if the position is ideal, trees respond slowly to changes. Flowering performance will be improved dramatically by exposing the tree to VERY bright hot conditions in summer.


Watering Serissa Bonsai

Watering serissa is where almost everyone goes wrong and where most problems occur. If you serissa is in a good free draining soil like watering will be easier. However watering should always be done in relation to the needs of the tree. A plant growing in a fine fibrous soil will require less frequent watering than one growing in a coarse open medium. The secret to watering is to allow the soil to dry a little between watering to the point where the tree JUST begins to wilt. Just before this happens the leaves will lose some of their natural sheen. However you will need a skilled and experienced eye to recognise the exact moment. Practically, watering should be performed when the soil surface feels dry to the touch. Then enough water should be applied in order to thoroughly soak the root ball ALL the way through. Watering will then not be required until the surface feels dry to the touch again.


Fertilising Serissa Bonsai

Fertilising serissa follows exactly the same rules as for all bonsai trees.

1. Never fertilise a bonsai that is NOT actively growing. So, no fertilising in winter, after re-potting or any other period in which the tree is not putting out growth. Fertilising will not cause a tree to grow, it will only help support existing growth as it happens.

2. Never over fertilise. More is not better. Only ever use fertilisers as instructed by the manufacturer. Never use garden fertilisers for bonsai, use a product specifically designed for the unique situation in which bonsai grow.

3. NEVER....EVER...EVER fertilise unhealthy trees or those stressed by environmental changes. Fertilising sick or struggling bonsai will only make matters worse and will add insult to injury. Inappropriate use of fertilisers can kill bonsai trees.


Overwintering Serissa Bonsai

Overwintering serissa bonsai is a skilled job and requires a little more care than some species. Our homes are too warm and dry for most plants and in winter when light levels are low a very warm situation will encourage the tree to grow. However the light levels are not sufficient for good strong growth to be formed. Also there is insufficient light to maintain the trees energy levels and so a tree that is too warm will quickly put out long thin leggy growth that is pale in colour. Over time the tree will become weak. Because the growth is very weak it appears to droop and so most folk water more which in turn encourages more weak leggy growth. It only takes a couple of months for this situation to become fatal to the tree.

Over winter a serissa will need to be kept cool, ideally 3-8 Celsius. At the same time the soil must be kept BARELY wet, but, not completely dry. This situation coupled with low light levels will cause the tree to go dormant and it may shed most of it's leaves. In spring when light levels improve simply return the tree to it's summer quarters, resume normal watering and wait for strong new growth.


Summary of Serissa as Bonsai

Serissa is a very beautiful finely detailed tree that makes the best quality bonsai that can be cultivated indoors. However it is only for the skilled bonsai hobbyist, ham fisted beginners should give it a wide berth and concentrate on developing their skills with other varieties. If you do not have the skill, knowledge and more importantly the facilities to keep and overwinter this tree move on. Serissa is a tree that rewards a skilled hand and will respond very positively to training and, given time, will make stunningly beautiful bonsai. My first bonsai was a fine serissa which I killed within two years. Now 25 years later I still have a soft spot for the variety but, thankfully don't manage to kill them any more.

Graham Potter
© Kaizen Bonsai Ltd 06/2014