Hoya undulata was described in 2015 and is endemic to Borneo in the Kalimantan portion only. It lives in the lowland heath forests at about 350 meters. It was named for its undulate leaf margins. The corona lobes have two hooked appendages that are only found on this Hoya and Hoya griffithii.
There are difficult Hoyas and then there extremely difficult Hoyas; Hoya undulata falls into the latter category. I failed with my first plant obtained from AH Hoyas in 2016, and with my second one in 2017. After killing my first two rooted cuttings, my friend Jimmy from NC sent me a third specimen in 2018. My plant kept going downhill, and just before it was ready to expire, I pulled it out of its pot and tied it on to my very large Hoya imbricata mount. It surprised me there and actually started to grow, and even went so far as to forming a peduncle, before it fell off.
My mounted plant started to gradually look the worse for wear after having it outside during the summer of 2019. I knew that I was not going to bring that large mount back inside and try to make room for it, for yet another year, so I finally took two cuttings from the plant, and hoped for the best. One cutting made it, and that is the plant that I currently have. After 2 or 3 years of trying to grow this plant I was back at ground zero with a newly rooted cutting. This time I had the plant in a net pot so that I could more easily ascertain when to water it. My friend Jimmy in NC is a remarkable Hoya grower and gave me some advice on how to grow Hoya undulata. He said to only water when dry, no more than once a week, and grow it on a heat mat. This advice made all the difference, and my plant actually started to improve and grow. In January of 2020, I saw a peduncle begin to form on the plant and I began the very long vigil. When it began to form buds I was ecstatic!
As my buds grew larger, I was disappointed that my plant began to look worse, and worse, eventually losing three leaves. All I wanted was for at least one of these buds to open so that I could finally say that I flowered the plant. I was checking these buds night and day, before I finally checked it about 9:00 pm before going to bed and saw that it had opened three flowers! I new nothing about the flowers, and had no clue how long they were supposed to last, so I was very nervous and decided that I needed to take some photos that night. When I picked up the plant, one of the 8 buds fell off, which was even scarier; I had to take photos very soon, or I feared that they would all drop off. The next morning there were still only three flowers opened up, but what magnificent flowers they were! 24 hours later the remaining flowers opened, and what a magnificent sight. There was something really special about these blooms. I can now report that the flowers on this plant are very short lived, falling off after only about three days. Four years of hard work for 3 days of glory, I will leave it to you to tell me if it was worth it.
Because the considerable difficulty in cultivating this Hoya, I cannot give it an enthusiastic thumbs up. However if you are looking for a capstone challenge with your Hoya growing, then you will have to look far and wide to find a better candidate. Here are the conditions under which I believe Hoya undulata would grow best. Warm and humid, temps above 75 degrees F day and night, don’t give too much light as most LEDs stress the leaves and they turn red as a result. Water when almost totally dry; cross your fingers and hope for the best!