The Ochna serrulata makes an interesting outdoor bonsai subject for growers in Zones 14-24, or anywhere with winter protection. Its foliage is attractive as the leaves change color during the seasons, its flowers are striking, and the seed formation is unique. This evergreen shrub from South Africa has a slow-growing, spreading habit and a trunk that can develop the character traits that are desired in the cultivation of a bonsai.
Ochna serrulata prefers a soil that is slightly acidic and should perform well in most bonsai mixes. A balanced fertilizer should be used most of the year, with attention paid to iron to maintain the deep green leaf color. As winter approaches, switching to a 1-5-5 fertilizer will reduce leaf flush during the coldest months, while still providing the right balance for maintaining root health and preparing for flower bud development. As with most bonsai requiring iron, I like to add a couple of non-galvanized washers or spent nails to the soil mix. The acidic soil promotes the rusting of the iron providing a satisfactory iron chelate for the plant.
Ochna serrulata has durable fine-toothed oblong leaves that are a bronzy color as the plant flushes out with new growth during the spring, which then changes to a rich deep green as the leaves mature. The serrated leaves have barbs, but they are soft barbs, that are visually pleasing and easy to work around. The flower buds are held close to the stem and will develop into bright yellow buttercup-type blossoms in early summer. The flowers themselves are very attractive, but the spent flowers are unique. The yellow flower petals will abscise, but the sepals will remain and slowly turn an intense red color. From the center of the red sepals green seed fruits will develop, ripening to a shiny vivid black color. When the fruits have ripened, the appearance of the black fruits against the red sepals looks very much like the eyes, ears, and nose of a mouse. This is why the plant is often referred to as the "Mickey Mouse Plant", and a reason why young and old love it.
When pruning Ochna serrulata, plant form and structure should be considered. It is necessary to prune to regulate growth and remove root suckers and trunk sprouts emerging from latent buds. You will also want to thin overly dense branches from the miniature canopy that may reduce air circulation and light from reaching the flower buds. To increase bonsai height, pinch or cut out the growing tips of the lateral branches. To increase the fullness, pinch or cut the terminal buds at the end of branches. Location of your cuts is important. If it is too close to the vegetative bud or flower spur, the bud or spur may die. If too far from the point that you want to induce growth, an inactive stub will remain that, lacking metabolic activity, will usually shrivel, desiccate, and abscise, leaving dead tissue that may leave an entry point for disease. In most cases, the cut should be about one quarter inch from the bud you want to encourage, and the cut should be made at about a forty-five degree angle so that the apex of the cut is above the bud.
I want to emphasize the importance of a sharp tool for all garden pruning, whether it is a pruning knife, shears or saw. Nice clean cuts will callus over more quickly and easily than ragged cuts that have torn the bark. If the cuts are clean, the active cells in the cambium layer of the stem or branch will grow inward and neatly close off the open wound. (Writing this short article on Ochna, made me realize, that perhaps more complete information on pruning plants in general, should be the subject of next few articles.
Because Ochna serrulata likes a bit of shade for best performance, it should make a great bonsai for any balcony that is not south facing in Zones 14-24, or anywhere with winter protection. With attractive foliage, striking flowers, and unique seed, this slow-growing shrub can be trained to develop the character traits that are desired in a bonsai subject.
Copyright: Gilbert Foerster/2010
