If you have to travel, or don't always get around to checking plants to see if they need water daily. There are some succulent or desert trees that can go long periods without water that make interesting bonsai. Already mentioned is Portulacaria afra. But my favorite genus is Bursera. Bursera is a genus of plants that are also known as Copal or Linaloe, the resin of which has often been used by the Mayan and Aztec as incense and as an ethnobotanical herb. The resin has some topical antiseptic properties. I really love the fragrance released any time you touch the leaves.
Bursera microphylla, and fagaroides, and or just about any species of Bursera from Mexico. The species from Florida, Bursera simaruba, has larger leaves and is not as "good" for bonsai. The leaves are compound for most but are only 3 lobed for most of the Mexico species and are relatively small, so the usual issues with excessively large compound leaves are not a problem. These are arid land shrubs, and can be dried out between watering. So if you "have a life" and can not water frequently. During warm weather of summer, think the August "monsoons" that hit northern Mexico and Arizona, Bursera can be grown moist, warm and sunny. They will grow rapidly. But as soon as the weather cools, dry them out between watering. In winter, they stay on my windowsills, and often only get watered once a month through the winter. They will grow opportunistically, sun, warmth (above 70 F) and water like a normal houseplant, they will keep growing. But as soon as the windowsill cools below 70 F at night, start letting them dry out, as growth will slow. If you keep them cool and wet they will rot away. Let them dry out in autumn. Most of the leaves will fall, but not all. Then water only after pot has been dry a couple days. Larger specimens, more than 2 inches in diameter, you can stop watering in autumn and not water again until spring and not harm the tree at all.
I grow them in 50% crushed granite, 25% pumice and 25 % akadama. You can substitute potting mix for the akadama. In other words, the potting mix is quite dry and does not retain moisture. The crushed granite is grit for poultry. Make sure the grit you buy is just crushed granite or crushed quartzite, without oyster shell or "attractants" to get the birds to peck. Some grit for pigeons will have sensen or anise seed added to attract the birds.
These are great little trees, somewhat hard to source, real collector items. They make amazing low maintenance windowsill bonsai.
