I have been trying to find information on the Hoya plant commonly known as "Sweetheart Plant" and a picture and have had no luck. Can you help?I would have to believe that Hoya kerrii is named 'Sweetheart Plant' or Sweetheart Hoya" because of the 'heart' or 'valentine' shaped leaves. These plants are found growing naturally in Thailand, Malaya and Sumatra.
Hoya kerrii has thick, succulent type, opposite leaves that are indeed shaped like flat hearts. The leaves are joined to the long, twinning stems (by the sharp tip of the heart-shape leaf) with ½ to 1 inch long, 1/8 inch thick petioles (leaf stalks). The stems produce aerial roots which in their native habitat grow into deposits of humus found in crevices and branches of trees as well as absorbing moisture from the air. These aerial roots root easily when inserted into a moist medium making it easy to propagate new plants from stem cuttings. Hoya kerrii also comes in forms with variegated leaves.
The flower shape is typical of hoya plants. Small, flat, star-shaped individual flowers are joined like ribs of an open umbrella to form a cluster that is attached to a spur (single stem) called the peduncle. Each small flower is made up of two stars, one on top of the other. The so called bottom star (corolla) is larger in size than the upper centered star which is termed the 'corona'. Hoya kerrii has whitish corolla's and reddish corona's. The flowers are very beautiful, waxy, tough and long lasting. All hoya flowers have wonderful fragrances, some very powerful, others less so.
Hoya plants will flower profusely year after year as long as they are given a few basic requirements. New flower buds grow from the old spurs (peduncles) along the vines, so needless to say, these must not be removed after the plant has completed blooming for the season. Some folks like neat compact plants, so they cut the long vines with the flower spurs off, and then wonder why their hoya won't bloom. I loosely tie the long hoya vines to homemade fan shaped trellises which keeps them upright and proudly showing off their beautiful flowers. More often then not, the same spurs will bloom two or three times in one season. When they are in full bloom, the whole house smells like a chocolate or candy factory. Never move or disturb a hoya plant once the buds have formed.
Hoya roots cannot stand excessively wet soil or they will rot. A porous, rich, well-drained media is what the plant requires for healthy, vigorous growth. My favorite mix is 1 part loam, 1 part sphagnum peat moss, ½ part perlite and ½ part vermiculite. To this mixture, 11/2 tablespoons of bone meal is added per gallon of mix for good root and flower bud development. Soiless mixes may also be used and are available at most garden centers. When using a soiless mix, the plant must be fed more frequently than one with a soil base. The medium must be moist before the plant is fertilized, or root injury is possible. Hoya's prefer a fertilizer with a higher phosphorous percentage which is indicated by the middle number, such as 5-10-5. The plant should only be fed every 6 - 8 weeks while it is actively growing in spring and summer.
Without bright light, there is no hope for flowers. The best possible spot is about 3 - 4 feet back from a south facing window so the plant does not receive the direct hot afternoon sun in summer. The low winter sun provides the required bright light needed, but is not strong enough to damage the leaves. If located in east or west windows, the plants should be allowed the direct morning and afternoon sun. If artificial light is the only option, provide at least 450 - 800 ft. candles of light for 8 - 10 hours per day.
Hoya plants need to be a bit potbound before they will bloom. In many cases they simply will not bloom the first or even second year until adequate roots have formed. A slightly potbound plant will put its energy into growing leaves and flowers rather than producing a larger root system. With some of the larger species the plant will not bloom until the stems have reached at least three feet in length, or longer. Under ideal growing conditions, however, stems can grow 6 - 7 feet in one season, many reaching lengths of 15 feet. Check the root-ball occasionally by taking the plant out of the pot . If only a few roots are visible, the plant does not require repotting. If many root hairs are visible, than repot it in a one size larger pot in the spring before flowering begins.
As previously mentioned, hoyas can be touchy with their watering habits. If a plant is watered before it really needs watering, the whole lot of blossoms may drop to the floor before opening, or the roots may rot. So, while the plant is actively growing in the spring and summer, drench the soil and let it dry to about 1/2 inch below the soil's surface before watering again. In the plants semi-dormant period (late fall and winter), the soil may be allowed to dry even more (almost completely) between watering. The drier soil in the dormant period helps with flower bud development as well as preventing the roots from rotting. Never allow a pot to sit in excess water and be sure drainage holes in the pot are always open to allow excess water to drain freely.
As for temperature, the average home room is fine. Night temperatures of around 60 degrees F. is best for the plant with daytime highs near 72 degrees F. Hoya's have survived in much cooler and much warmer temperatures, but in the home this would be uncomfortable for people.
The one thing hoyas must have besides a very well-drained soil, is a rather high level of humidity during the entire year. The combination of drier soil and moist air in the winter months is necessary for the health of the foliage as well as good flower bud formation in spring. Very dry air can result in drying, yellowing and falling of leaves. Older plants will drop the odd leaf from time to time, but this is normal. Grouping of plants, pebble trays of water, moist sphagnum peat moss, humidifiers or misting the leaves several times a day (not at night) will help raise the humidity levels in a room.
Hoya plants are easily propagated in the spring between May and June by taking cuttings of new growth. Each cutting should have 2 to 3 nodes (joints). Remove the bottom leaves from the cuttings, insert them in moist sand or vermiculite and keep them warm and moist. The cuttings may take some time to develop a root system, so, feeding them with a ½ strength water soluble fertilizer every 6 - 8 weeks is beneficial.
Mealybug is the main predator of hoya plants above the soil line. These insects lure in the leaf axils and stem joints of the plant, sucking on the plants juices. They must be controlled immediately by touching them with a cotton swab dipped in alcohol, or spraying the plant with malathion. ALWAYS READ AND FOLLOW DIRECTIONS AND PRECAUTIONS ON PESTICIDE LABELS.
One final word of precaution - hoyas can be addicting! Once addicted, you may have to add on to your home as new species arrive.
