Plant ID: Pachypodium sp.

Question:
I was given this cactus as a present from a supply house here in New York that no longer exists. My plant consists of four stalks, the tallest of which is about 40" tall from the top of the 11" diameter clay pot in which it is planted. In their heyday, each stalk put out a grand splay of green leaves at their top which would replace itself except for a slow period in the winter.
I water the plant once every three weeks by immersing the pot but don't know whether I should be wetting the leaves and stalks at the same time. I have had good reaction to Miracle Grow once or twice a year. The plant sits on the window sill of a New York City apartment and gets direct sunlight for perhaps 2 or 3 hours a day. I have not seen any evidence of bugs or other infestation but have sprayed it on occasion with Safer Soap on the recommendation of my local florist. During the last year it has passed through several phases of losing almost all its leaves, which eventually come back but not in the solid, full spray of the past. The tallest stalk now puts out leaves but they almost all start to shrivel and darken before they have fully grown.
So, doctor, that is my problem. What am I doing wrong? What can I do to bring it back to its former great self?

Answer:
Your cactus belongs to the genus Pachypodium. Pachypodiums are native to southern Africa and Madagascar. These cactus-like deciduous succulents are used to much warmer and dryer climates and should not be subject to temperatures below 50º Fahrenheit. In total there are about 17 recorded species of Pachypodium. Even though I cannot identify the species with 100% confidence, I might guess that you own the species Pachypodium lamerei. Pachypodium lamerei I have seen written up as a viable houseplant in the U.S. since it does not get nearly as large as some of the other species. A good ID tool for these plants is the flower (color, size, fragrance, etc), so if you have ever seen it flower that might help us identify your plant more specifically.

Regarding caring for your Pachypodium, they do prefer full sun and a fertile soil with maximum drainage. They can be watered with regularity during the active growing season from late spring through summer. Since you have plenty of new growth in the form of those small side shoots I would say your watering every three weeks is fine. As the saying goes, “if it ain’t broke don’t fix it”. However, since I know that this genus of plants goes dormant in the winter, I think you should cut back gradually on the water so that you are applying less or none in winter. As the days shorten and there is less sunlight for photosynthesis, the plant will begin to slow down. Perhaps water only once in November, once in December, and once in January. For late January and February do not water at all. You would then begin watering again, starting in March with smaller amounts and eventually getting back to the full submerging by the end of April or May. As for the Miracle-Gro, I would only apply it once a month when you water during the active growing months from June to September. It is best to repot in springtime while the plant is resting and before it becomes very active again. Schultz (I believe) actually has a soil mix that they advertise as being best for cactus and succulents. The label is quite clear, and I have found it in garden shops of all shapes and sizes around the city. The soil itself I have had good success with. I have even used regular potting soil with sand mixed in, but sand alone is not always as easy to come by in the city.

Finally, let’s revisit some of the issues you have noticed recently. The pinched deformities to the leaves on the tallest stalk are some kind of insect damage. To combat this, I believe that the insecticidal soap is your best bet. Safer is a popular company and I can stand behind their whole line of insecticidal soaps ready to use in spray bottles. You might want to treat a single leaf before applying the spray to the entire stalk, but the leaves seem sturdy and glossy enough that they should hold up just fine. Looking at the brown and black leaves, I would guess that those might be caused by a nutrient deficiency. As we have already discussed, since you have not repotted the plant in the four years you have had it, I would recommend changing out the soil. Fresh soil should allow for adequate nutrients and drainage for the plant. It seems as though the size of the container still allows for ample growing room so I think you can use the same pot when repotting. As far as the best order to control these issues, I would try and treat the deformed leaves and pest issue now and wait until spring for the repotting.