Clerodendrums are a large group of deciduous and evergreen trees, shrubs and woody climbers that flower late in the year. Most of them grow wild in tropical and subtropical countries, they are found growing wild in four of the five continents, the exception being Europe.
Clerodendrums, commonly known as Glory Bowers, are grown for their pretty flowers and attractive leaves. The shrubs are suitable for a warm border or trained as a climber over a trellis, pergola or other support. In frost prone areas, grow the frost tender species in a warm glasshouse or conservatory.
When grown in a greenhouse plant them in a large pot, in full light with shade from hot sun in summer. Water freely and apply a liquid fertiliser monthly from April to August, water sparingly in winter. They can be grown outdoors in frost free gardens. Plant them in a fertile, humus-rich, moist but well drained soil in sun or partial shade.
Clerodendrum bungei (Glory Flower) is a variety, native to China, which we can grow in Ireland. It is a plant that is fairly easy to grow as long as you give it a reasonable well drained soil, some shade from the hot sun and some moisture. It flourishes in the shade of large trees where it will grow into a vigorous suckering shrub producing numerous straight, deep-purple suckers around the parent plant. The real joy of this plant is its wonderful flower head that is produced from late summer to autumn.
The flower is made up of pink petals with deep pink buds behind the petals and it’s this combination of two-tone colours that looks terrific. After flowering, prune these plants close to ground level to produce a multi-stemmed shrub that will produce more flowers the following year. It grows about six feet tall and produces large heart-shaped leaves.
The leaves have an unpleasant smell when rubbed.
Clerodendrum thomsoniae is a tender variety, suitable for the greenhouse. It is a twining, evergreen climber that produces white, bell-shaped flowers with a crimson tip in summer. Clerodendrum trichotomum is a bushy, deciduous shrub that will grow outside in the garden. From late summer to autumn it produces white flowers with red sepals.
After all the fine weather we had over the last few weeks it is easy to forget that as we move into November temperatures can drop to give us the first winter frost. Recent winters have been mild with little or no severe frost. It is nearly six years since we had severe periods of frost and snow leading to roads, schools and other closures but it was also not good for tender garden plants and this wasn’t as prolonged as the winter of 1963 though it was colder hitting a chilly -17.2C in Co Mayo.
Cold weather and particularly frost, causes the water in plant cells to freeze, damaging the cell wall of plants. Frost damaged plants are easy to see, their growth becomes limp and blackened. Frost problems are often made worse where the plants face the morning sun, this makes the plants defrost quickly and damages the structure of the plants.
Hardy plants and tough evergreens can also be damaged by long spells of frost. In this case the roots are unable to take up water and plants will die from lack of moisture, a winter mulch will help to prevent frost getting at the roots. Periods of cold, frosty and easterly winds during April and May can also kill new growth, blossoms and fruit.
In recent years we have grown an ever increasing number of tender plants that will not withstand a sustained period of frost without some form of protection. We cover the top of the trunks of our tree ferns, Dicksonia antartica, with fibreglass insulation, we also put some fibreglass into the crown. The crown at the top of the trunk is the most vulnerable part of the plant.
Tree ferns are slow growing and expensive plants to buy so it is well worth protecting them from frost. Tender cordylines and palms can be protected in the same way. Protect tender rock garden plants with a layer of gravel or grit to ensure swift drainage of water away from the leaves.
We grow some of our cannas and yuccas in containers that are moved to the greenhouse for winter protection.