The main exception to this general rule is P. namaquanum, which comes from the winter rainfall area of southwestern Africa. This species usually goes dormant in the summer and does not enjoy lots of water during this time (real risk of rot when left unprotected in summer rainfall climates). This is an excellent choice for mild Mediterranean-type climates like southern California.
On the large side for the shrubby plants, relatively common and easy compared to other members of this group, is P. saundersii, which reaches a few feet high and wide in old age, with white flowers. This smaller relative of the bottle tree P. lealii grows a fat main caudex low to the ground and lots of sprawling, spiny branches with leaves near the end. Another attractive but extremely rare shrub in this size range is the bottle plant P. ambongense.
Smaller yellow and white-flowered shrubs and sub-shrubs from Madagascar include P. densiflorum, P. eburneum, P. horombense, and P. rosulatum. The lowest, weirdest and touchiest Pachypodium is P. brevicaule, which normally makes yellow flowers but has a white-flowered form (leucoxanthum). These plants generally require summer heat to really thrive.
Two South African plants grow below-ground stems: P. bispinosum and P. succulentum. The only reliable way to distinguish them is by the shape of the flower. They are typically more resistant to cold temperatures and do not go completely dormant in very mild climates. They may also flower at various times of year. The above-ground portion of these plants consists of spiny, skinny, sprawling branches, though they are often lifted after several years in cultivation to display the fat caudex, which grows larger the longer it’s left undisturbed. Protect a lifted caudex from direct sun to avoid scarring.
Given good drainage (50% pumice, perlite, or equivalent) they enjoy much more frequent water than most succulents, and should be treated like Adeniums during this time of year. Allowing the soil to stay dry for any extended period during summer may result in growth arrest and loss of roots, and is not recommended in containers, especially for the touchier plants like P. brevicaule (desirable for its low, blob-like shape) and P. windsorii (desirable for its unusual and striking red flowers).
During the colder months they may lose some or all of their leaves, and some go completely dormant (especially the Madagascar species). All Pachypodiums with an above-ground caudex are sensitive to cold and require protection during winter near freezing conditions. During cold weather dormancy they are particularly sensitive to rot in response to excess moisture, so water carefully and infrequently at this time. The two common tree species can handle winter rainfall just fine in a climate like mild coastal southern California, given good drainage. The others vary in their tolerance.
In mild climates Pachypodiums may not actually go dormant in winter, or the dormancy may be greatly reduced in duration. This is especially true of the plants with underground caudices. The winter-growing P. namaquanum is a better choice for mild winter rainfall climates if the plant is going to be left outside. Be aware this species requires very strong light during winter, which makes it impractical as a house plant.
Provide young seedlings some protection, strong light, excellent drainage, and regular water during the first year or more of growth. Do not allow the soil to go completely dry or stay dry during this sensitive early period.
