Hoya is the botanical name for plants that we in Sweden call
“porcelain flowers”, wax plants in English. We all know Hoya
= small wax flower and Hoya carnosa
= the ordinary wax plant, which have been grown in Sweden since
Hoyas belong to the
Asclepiadoideae in family Apocynaceae. This subfamily
was formerly a family of its own,
belonging to the same
are Stephanotis, Ceropegia, Stapelia and several more. In Sweden
you can find only one wild growing relative, swallow-wort
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.
Most hoyas are epiphytic vines
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
At the nodes the flower spurs are developed. Do not
form new buds again.
The flowers always consist of
calyx, corolla and corona, all formed as
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
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
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
name Hoya carnosa. So
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,
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
indoor climate well. They do not need much
and grow and flower very well without
care. But they
like being looked after sometimes – a shower
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.
Plant the cutting directly in a small container with porous
potting medium (see
Put the cutting
first pair of leaves
hit the medium,
growth hormones are concentrated
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.
that the plant is evenly moist,
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
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
long dry periods
even watering. The best way of knowing when to water is to
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.
Clay pots are stable
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
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
Choose a house plant mix of good quality. Vermiculite
potting medium moist for a longer time
– you do not need to water that often. The perlite makes the mix
more porous and
the roots. A layer of big sized leca grains in the bottom of the
container is a good way of providing drainage – poor drainage
kill the roots. If you cannot
vermiculite and perlite, use
leca grains. Some
hoyas like calcium.
You can add some lime to the
just top with
This advise is for indoor growing.
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
Mealy bugs, much enlarged