As I shared above, many hoya have adventitious roots along their stems and these roots are used to both adhere to surfaces as well as absorb moisture. Upping the humidity will likely form more roots and make them larger, which will benefit the hoya. Since most hoya are epiphytic—growing on the surface of trees—they are accustomed to drying out, so they are a bit opportunistic when it comes to getting water, and these adventitious roots can serve as a way to soak water when they have it. However, giving hoya too much water for too long will not serve the plant. In fact, it will likely harm or even kill the plant, so it’s imperative that it is potted in some well-draining potting medium.
More semi-succulent varieties of Hoya carnosa were my first hoya that I grew and I made the mistake of putting them too near my southwest-facing window, which caused leaf burn. Most hoya (with exceptions) can’t withstand such direct, intense light. Since most species grow in the gaps of forests—among and between the treetops—they are more accustomed to getting dappled or diffuse light—and that should be recreated in the home.
When visiting different botanic gardens and growers of hoya, it is customary that they grow hoya under 50-80% shade cloth to protect from direct sun. I’ve found that more succulent varieties, like Hoya kerriii, Hoya crassicaulis, and Hoya diversifolia can withstand about 90% full sun conditions, but would still prefer a little less sun for fear that the intensity of the ultraviolet rays would break down the chlorophyll in the leaves. In some cases, certain varieties might begin to redden their leaves (e.g., Hoya vitellina), which can be pretty, but you have to be careful not to fully burn the plant and damage the chlorophyll in the process.
I have most of my hoyas growing in one of several locations in my home: pulled away 1-4 feet (0.3-1.2 meters) from my southwest-facing windows; in my northeast-facing windows; near my northeast-facing windows and augmented with grow lights; and completely under grow lights.
Most hoya don’t mind being a little rootbound, as they are used to growing epiphytically, so I don’t often repot my hoya. Instead, I just refresh their substrate every second or third year or so. Given that I’ve been growing some of my earlier hoya for around four years now, that means I’ve repotted them once, and will be repotting some of them again sometime soon. Because they like to dry out more than most plants, I prefer to use terracotta pots since they are porous and can more readily remove water from the soil substrate or potting medium—but do be sure to thoroughly water them so the entire soil ball becomes wet and is allowed to dry.
Soil / Substrate
Hoya, particularly the epiphytic ones, are accustomed to growing in very little substrate, so it’s not uncommon to find hoya mounted on wood and wrapped in Sphagnum for display in one’s home. Because of the lack of substrate in these displays, you’ll likely need to do more frequent watering. I have one of these displays in my bathroom of a Hoya pachyclada and I find I need to spray the roots every few days, and I treat it much in the way I do my Tillandsia, or air plants. Putting the mounted hoya on the same watering schedule as my Tillandsia has helped a lot.
Otherwise I find it easier to care for hoya in substrate. In Asia, it is customary to grow hoya in pure coco chips. Generally my potting mix is about ⅓ peat, ⅓ perlite, and ⅓ orchid mix (fir bark, perlite, charcoal). I find this gives a fairly airy mix. This is particularly important because hoya don’t like to be sitting in water. They require intermittent drying out. If they don’t dry out—they’ll rot pretty readily. But if they don’t receive enough water—their roots will often dry out and die back. (More on this in the Troubleshooting section).