What is
Hoya

What is Hoya?

Hoya is the botanical name for plants that we in Sweden call “porcelain flowers”, wax plants in English. We all know Hoya bella = small wax flower and Hoya carnosa = the ordinary wax plant, which have been grown in Sweden since about 1880.

Hoyas belong to the subfamily Asclepiadoideae in family Apocynaceae. This subfamily was formerly a family of its own, Asclepiadaceae. Other genera belonging to the same subfamily are Stephanotis, Ceropegia, Stapelia and several more. In Sweden you can find only one wild growing relative, swallow-wort (Vincetoxicum hirundinaria).

Where do they come from?

Hoyas grow wild in Southeast Asia from India in the west to Polynesia in the east. The northernmost border is the south of China down to the northern parts of Australia.

What are their main characteristics?

Most hoyas are epiphytic vines while some are terrestrial vines and a few ones are woody scrubs. In cultivation some of them do well in hanging baskets but most of them need some kind of support to cling to. The stem, like all parts of the hoya, contains sap which can be milky, clear or orange coloured. The leaves are opposite, mostly in pairs. They are placed at the node which is the place where new roots are formed easily. At the nodes the flower spurs are developed. Do not remove them as they often can form new buds again.

The flowers always consist of calyx, corolla and corona, all formed as five-pointed stars. They grow in umbels  and the number of flowers per umbel varies from only a few up to one hundred. There are also a few single flowered species. The size of the single flowers range from a few millimetres up to about eight centimetres. Many hoya flowers  give off a sticky nectar when flowering. Another characteristic of hoyas is that their fragrance is stronger at night, probably they are pollinated by night active insects.

How many species are there?

Today we do not know exactly how many species there are, but an estimated figure is 200 – 300. Many new species are still being found. But there is big confusion concerning the names. Many species have been described and named by different people during the 200 years since the first one was given the name Hoya carnosa. So one single species can have two or even more names. In that case the oldest name is the valid one.

How come? Well, new species or clones of “old” species are still being found, and it is not always easy to tell if you have found a new species or one that has already been identified. Until it is identified the plant gets a temporary name. It always start with Hoya sp.

Sp is short for species. Consequently there are different species named Hoya sp. Sulawesi. It only means that the plant was found on the island of Sulawesi and that it is unidentified. As there may be many unidentified plants from the same place, an ID is added which often consists of the collector’s initial letters and a serial number. If you have or obtain a hoya with letters and numbers after the name it is important that you keep the label attached to the plant. It works as a personal code number.

How do you obtain hoyas?

In the last few years it has been possible to find several hoya species at flower shops and garden centers. The most common are Hoya bella, Hoya linearis and Hoya tsangii (often mislabelled as Hoya bilobata). If you cannot find any where you live, join our society. Then you will get in touch with other collectors and will be able to buy and exchange cuttings. You can also take a good look at our web site to get a tip where to find cuttings.

How do you grow them?

Unlike many other tropical plants hoyas are easy to grow. They like warmth and cope with our Scandinavian indoor climate well. They do not need much fertilizer and grow and flower very well without lots of care. But they do like being looked after sometimes – a shower now and then, does not do any harm! Hoyas do well in windows facing any direction. They do not flower much in a window to the north (there are a few exceptions) but they grow well if you remember not to water that often. The best is a window to the south or the west. But remember to protect the leaves from direct, burning sun light during the height of the summer.

Rooting cuttings

Plant the cutting directly in a small container with porous potting medium (see further down). Put the cutting into this until the first pair of leaves hit the medium, as the growth hormones are concentrated there. Place it in a plastic bag with a small hole for ventilation. The best place for the cutting is in bright light but with no direct sun light, if possible with some heating underneath. Make sure that the plant is evenly moist, neither dripping wet nor too dry. Open the plastic bag gradually and when the plant has started growing you can repot it in a bigger container. Cuttings can also be rooted in water or in moist sphagnum or perlite.

Watering / fertilizing

In the summer most hoyas need watering once or twice a week, but not that often during the winter. Hoyas are sensitive to overwatering. You should let the soil get a bit dry before watering. Thin-leaved plants cannot cope with long dry periods and prefer even watering. The best way of knowing when to water is to put your finger into the potting medium. When it comes to fertilizing it is enough with a couple of doses a year, in the summer. A dose with a high phosphorous fertilizer in the autumn encourages the flowering the following spring. Do not fertilize the plants until six months after repotting. The biggest reason why hoyas do not flower is too much fertilizer.

Pots

Clay pots are stable and they don't easily fall over – a hoya growing on a trellis can get very heavy. Clay pots also let through oxygen to the roots and breathe, unlike plastic containers which could also be good, as long as you remember not to water that often.

An example of a good potting medium:
50 % house plant mix
25% vermiculite
25% perlite

Choose a house plant mix of good quality. Vermiculite keeps the potting medium moist for a longer time – you do not need to water that often. The perlite makes the mix more porous and allows oxygen to get through to the roots. A layer of big sized leca grains in the bottom of the container is a good way of providing drainage – poor drainage may kill the roots. If you cannot obtain vermiculite and perlite, use the smallest sized leca grains. Some of the terrestrial hoyas like calcium. You can add some lime to the potting medium or simply just top with crushed shells. This advise is for indoor growing.

How do you fight pests?

Prevention is the best cure. Check new plants thoroughly and keep them isolated a few months. To spray or place the foliage in a solution of water, alcohol and soap is another good method. Isolation works best in a separate room. Another way is to place the plant in a plastic bag with a small hole for ventilation. This is not a totally secure method, but is quite good. Do not forget to clean the surfaces around the plant sometimes.

Common hoya pests are aphids, mealy bugs and scales. The simplest way is to stick Provado* tablets into the potting mix or to spray with Provado Plus*. The products are sold in flower shops and garden centers. Mites are eliminated by Provado Plus and Ardap*.
(* Provado is manufactured by Bayer and Ardap is manufactured by Quiko)

 

Mealy bugs, much enlarged