4. GROWING HOYA macgillivrayi
4a. SOIL AND CONTAINERS
A loose, friable, peaty soil mixture that is mildly acidic, moisture retentive and sharply draining is essential.
A potting mix that is not well drained and does not allow air to freely permeate it will usually cause the loss of the plant’s roots.
It is important not to use a container that is too large for the root ball. This can result in the compost remaining too wet for too long, again resulting in root rot. Equally, too small a pot can result in the soil becoming too dry. Similarly, consideration needs to be given to the type of material from which the pot is made, as this also affects the length of time that the soil remains moist, or becomes dry. This is particularly so in summer when the soil in unglazed terracotta pots will dry much faster than soil in plastic pots, as the moisture will evaporate through the sides of the terracotta pots; and in winter, when the soil in plastic pots tends to dry out much more slowly than it does in terracotta pots.
As an epiphyte H. Hoya macgillivrayi has evolved a shallow root system spreading laterally in whatever leaf litter is available. Therefore, a pot that is wider than it is deep, suits it much better.
4b. WATERING
Frequency of watering is an important consideration, in view of the fact that H. Hoya macgillivrayi will not tolerate stagnant soil conditions - and is especially so during winter in cool climates when the plant should be kept dryer - but not completely dry. In warm to tropical climates where some growth is made, watering can be adjusted accordingly.
Once the main growing season begins, Hoya macgillivrayi enjoys copious amounts of water, but only if the soil is sharply draining and the temperature and humidity are both high enough to support fast growth. If in doubt, wait for the soil to approach dryness on the surface before watering again.
4c. FEEDING
With any plant growing in a sharply draining soil, there is a greater need for regular feeding. However Hoya Hoya macgillivrayi , like all epiphytes, can suffer root damage if the fertiliser given at any one time is too strong. Fertiliser at ¼ to ½ strength should be given at every watering during the growing period, with a bloom booster supplied during the spring and summer, when flower peduncles are likely to be developing. It is important to aim for maximum growth and the maturing of both stems and peduncles during this period, as immature peduncles do not usually survive the winter.
During the winter, when growth all but stops in cool climates, feeding should be withheld as it is not then required by the plant.
In warm to tropical climates, however, where light levels and temperatures enable the plant to continue growing actively, feeding can be maintained. In intermediate climates where growth in winter slows down but does not stop, a reduced feeding schedule can be used.
4d. TEMPERATURE
During the growing season Hoya macgillivrayi enjoys daytime temperatures of between 80 and 90 degrees F. Ideally, there should be a drop of 10-20 degrees F during the night, in order for the plant to process the food it has made during the day. With temperatures in the 90’s and especially if grown under glass, air movement around the plant is vital in order to prevent heat damage.
During the winter in cool climates, plants growing under glass or indoors, need a minimum night time temperature of around 60F rising to 70 to 75F during the day.
4e. LIGHT
If grown in the home, in climates where light levels are reduced during the winter, it is important to give Hoya macgillivrayi as much sunlight as is available, by placing it in a south, or south-west facing window. With the arrival of spring and summer when light levels are increasing, it is happy in an east or south-east facing window with around 4 hours of direct sunlight during the day, or light dappled shade throughout the day.
4f. HUMIDITY
Hoya macgillivrayi prefers a high humidity of between 65 and 80% throughout the year; although in the home, the atmospheric humidity is often as low as 20%, especially where air conditioning in summer and central heating in winter is used. Very low atmospheric humidity will cause new growth to wither, flower buds to abort and potting composts to dry out too fast.
The atmospheric humidity can be increased by:
• grouping several plants together to form a microclimate around themselves
• regular spraying of the foliage during the daytime, particularly during the growing period, but also during the winter. Spaying the plant at night in winter should be avoided however, as this can cause chilling of the plant, as well as increasing the risk of fungal infection.
• filling a water-tight tray with a 2 inch layer of ‘Hydroleca’ (small, fired clay balls that are porous). Water is added to the tray so that its final level is about 1inch below the surface of the ‘Hydroleca’. The Hoya is then placed onto it. The ‘Hydroleca’ absorbs the water and helps it to evaporate into the air around the plant. It is essential, when using this method that the pot is not standing directly in the water, but is sitting on the ‘Hydroleca’ above it. If the base of the pot does stand in the water, the soil will stay continuously wet and become stagnant.
4g. AIR MOVEMENT
Air movement around the plant is essential:
• in summer, to prevent the build up of high leaf temperatures that can result in unsightly leaf burn.
• in winter, to stop the formation of stagnant air that can cause the development of fungal diseases, especially if grown in high humidity, such as under glass, and in cooler conditions.
Air movement can be supplemented indoors and under glass by the use of small electric fans placed in the vicinity of the plant, or by placing the plant outdoors, when temperatures allow for healthy growth.
4h. MAINTENANCE AND PRUNING
Little maintenance is required other than to regularly tie in the vines to a support to stop them from becoming a tangled mass and encroaching on neighbouring plants.
Long stems which have no peduncles can be cut back to a few pairs of leaves as the peduncles are only produced on new growth and will not form on stems once they are mature. New growth is usually produced on the uppermost parts of the stems and so pruning back these unproductive stems helps to rejuvenate the lower part of the plant, preventing it from eventually becoming bare. Those stems which do have peduncles should be retained, as they should develop flowers and continue to bloom from them in the future.
4i. PROPAGATION
Propagation of Hoya macgillivrayi is easy using cuttings from ripened stems with leaves attached, and from one to 3 nodes in length. They root quickly when placed in the humid conditions of a heated propagator, or zip-lock bag and kept at a temperature of around 80F. Adequate light levels are important for follow-on growth after the cuttings have rooted and so the best time in cool climates is in the spring, summer and early autumn. During late autumn and winter when, for example, cuttings may need to be taken in order to rescue a plant and where natural light levels are insufficient for growth, additional fluorescent lighting can be used, with the tubes positioned between 8 and 10 inches above the cuttings and left on for a period of about 16 hours per day. Once rooted, the cuttings can be potted up in a freely draining compost mix, as described above.
Cuttings also root in water and although successful, this method is usually slower than using a heated propagator, or zip-lock bag.
Image of Hoya macgillivrayi 'Superba' IML0220 (aka 'Big Mac')
