What to Plant in January

The following is a list of vegetables and herbs that  you can plant in January in Sydney, a temperate zone. Just click on the name for the growing guide for each vegetable or herb:

Plant of the Month – The beautiful Hoya

This month I am featuring the beautiful Hoya as Plant of the Month.

This specimen, Hoya pubicalyx, (native to the Philippines) with its beautiful star-shaped, fragrant flowers, has been growing in the same hanging basket in the same location under the eaves for nearly 40 years. Its vigour has waxed and waned through droughts, extreme summers and rainy winters and even neglect during Covid lockdown, but it is the great survivor and is currently flowering again.

As you may appreciate, the Hoya is a long lived plant that may be handed down through the generations if grown in optimal conditions.

The genus Hoya has over 500 accepted species of tropical plants of the Apocynaceae family, growing in tropical and subtropical Asia, Oceania, and the Pacific islands.

Hoyas are evergreen perennial creepers that can grow epiphytically on trees, twining and using adventitious roots. The stellate flowers come in various colours, including white, bright yellow, pink, orange, green, and blackish purple

Hoya leaves twining up a garden plant support.

Larger species grow 1–18 m, or more, with suitable support, twining in trees along trellises or hanging down from hanging baskets.

They also use adventitious roots that grow from the stem to help anchor the plant along climbing structures, trees, or even other adjacent plants. These adventitious roots can be seen in the image below.

Adventitious roots growing on a stem.

Hoyas have simple succulent leaves, arranged in an opposite pattern. These can take a variety of forms that may be smooth, or hairy. Some species have leaf surfaces flecked with irregular small silvery spots like my own Hoya. These add another level of beauty.

Hoya Pubicalyx produces a natural plant pigment “Anthocyanin” to protect young or soft leaves from intense light.

Beautiful silver flecked leaves of Hoya pubicalyx

The inflorescence is made up many flowers are formed in umbellate clusters at the tip of pedicels or spurs that are perennial and are rarely shed. These appear from the axils of the leaves and stems. As the plant flowers again and again at these spurs, it is important not to prune them away after flowering. (as my father did one year not realising their importance!)

The individual flowers will fall off the spur of their own accord. The image below shows a spur where many years of flowering have occurred. Each flowering increases the spur’s length.

A pedicel or spur showing the ridges where previous flowering occurred.

Expect flowers in the warmer months, in Australia from October to April. The frequency of the blooms depends on the species and on the care given. A hoya needs six hours a day of indirect sun to flower, growing in medium that drains well and that doesn’t get watered too frequently. My plant is hanging where it gets a little morning sun as it rises and then bright south facing light.

The flowers begin as clusters of closed, waxy, five sided stars as shown in the image below. The umbel or raceme is formed at the tip of the spur. Some have the older flowers at the outer edge and the younger flowers at the centre and a a flatter shape. Some racemes have stems all the same length and so form a spherical or convex shape.

The waxy unopened buds of the Hoya inflorescence.

Hoya flowers have three floral structures made up of modified leaves.

The first, at the tip of each stem has five small leaves of the calyx or sepal protect the emerging flower. These can be seen at the back of the flowers in the images below

The under side of the Hoya flower showing the five modified leaves of the calyx or sepal.

The next layer of modified leaves is the corolla. The five individual leaves of the corolla are commonly called petals.

The surface of the corolla is covered in tiny hairs that gives the flowers a sheen. The apex of each lobe of the corolla can be tipped or as in the Hoya pubicalyx it is turned under. This gives the lobes a rounded appearance.

Detail of the corolla and its hairy petals and the raised five lobed corona and drops of nectar exuding from their nectaries.

The third structure is the corona. It is a five lobed shiny, waxy structure that is raised off the corolla like a shiny star. The two modified leaves are fused into what is called a gynostegium the upper part which contains the ovaries. The lobes are not solid but rounded and wrapped around meeting in the tracks at each side of the lobes.The glands connecting the pollen sacs appear as black dots in these tracks between the lobes (see the detail in the image below).

Detail showing the tracks with the nectaries on the corona.

At the very centre of the corona are the five anthers that arise from the lobes and meet up like a small crown.

Detail with the five anthers like a small crown.

Nectaries produce nectar and store sweet substances, consisting of sugars (sucrose, glucose, and fructose), proteins, amino acids, and lipids as a reward for pollinators. Primary nectaries are located in stigmatic chambers and secondary nectaries in the corona lobe.

In the images below and above you can see the drops of nectar exuding from the nectaries.

Close up of the Hoya flowers.

The Hoya gives off scents that act as a way of attracting insects, and responding to pathogens. The sweet scent is given off from the biosynthesis of the chemical compounds in the plant tissues and cells and is most noticeable in the cool of the evening.

Below is another variety, Hoya carnosa with its delicate pink corolla and white and pink corona. Hoya carnosa has been cultivated for over 200 years and is easily grown.

The delicate pink flowers of the Hoya carnosa.

Studies at the University of Georgia, published in 2009, have shown Hoya carnosa to be excellent at removing pollutants in the indoor environment.

Detail showing an ant, a possible pollinator as well as the texture of its corolla.

Growing Hoyas:

The optimal temperature range is between 16-29 C but Hoyas will tolerate low temperatures though not freezing. However plants do benefit from the radiant heat from a nearby brick wall on cooler days.

Decide which method of training the Hoya that suits your location and that can provide the plant with shelter from droughts and indirect bright light. In the southern hemisphere this means a south facing location.

This may be in a hanging pot located under eaves or verandah, or a pot with a trellis in a sheltered site or even in a pot at the base of tree. I have seen Hoyas sucessfully grown as a screen in a shaded spot planted in long pots with a lattice structure behind for the plants to twine onto.

I have opted for a hanging basket and found that my Hoya has needed little maintenance over the years and the hanging pot also allows for easy repositioning if required. It has been growing happily in the same spot.

Soil choice should aim to create a mix that will re-create an environment similar to what they are used to in the wild. As epiphytic plants, Hoyas don’t require soil but the growing medium we use to anchor them for potting should be well draining and able to allow sufficient airflow around the roots. Avoid mixes that retains too much moisture such as those with wetting agents. Home made mixes can be easily made

You can make a medium with 2 parts coir and 1 part perlite.

You can also use 1 part succulent and cactus potting soil, 1 part perlite and 1 part orchid mix.

When choosing a pot, plastic pots are commonly used but unsealed terracotta is porous and reduces the risk of the plant becoming waterlogged and causing root rot. Always ensure that there are adequate drainage holes at the bottom to allow excess water to drain.

Hoyas do prefer to be a little root bound so a smaller pot is the better choice. This limits the amount of possible excess moisture around the roots from the extra soil. The pot should be slightly bigger than the root ball, or around 2-5cm larger.

It is best to allow the plant to dry out before watering. Water from the top until water runs out the drainage holes and do not allow the pots to stand in saucers of water as this will risk root rot. Water well then allow the pot to dry out before watering again.

Water according to the season. In the growing period of Spring and Summer water every two weeks if the soil is dry. In the winter opt to keep the Hoya on the dry side as the humidity in the air will help. This will mean that after checking the soil moisture perhaps watering once a month or so.

The rule of thumb for watering then, whether grown indoors or out is providing minimal watering and ample humidity.

Hoyas can be propagated in rain water from cuttings. The adventitious roots will grow into a suitable root ball for planting.

Roots developed from propagating a stem in water now ready for potting.
The beautiful and delicate inflorescence of the Hoya pubicalyx.

Hoyas are easy plants to grow that are able to survive a little neglect, but will put on a stunning show of blooms when properly cared for and located in an optimal site. I hope this will encourage you to research further and seek out one for your home.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s