Growth Requirements
General
The seeds of Canavalia pubescens sprout easily (after scarification), and, initially, young plants grow quickly and are easy to care for. However, maintaining this ʻāwikiwiki species long term can be challenging and demanding because of repeated and severe attacks by arthropod pests, primarily lace bugs and spider mites (see below for further discussion). Therefore, if you feel you don't have the time to closely monitor for and quickly take action to control these pests, you may want to opt for a less-demanding species of native Hawaiian vine such as maile (Alyxia stellata), Bonamia menziesii, Gouania vitifolia, or pāʻūohiʻiaka (Jacquemontia sandwicensis). Additionally, in my (Koebele) experience, the O‘ahu endemic ʻāwikiwiki (Canavalia galeata) is a bit easier to maintain than C. pubescens; however, C. galeata requires a wetter habitat.
Canavalia pubescens is a climber. Therefore, consider planting it near a fence or using a trellis. In the wild, it can be seen climbing up wiliwili trees (Erythrina sandwicensis). However, C. pubescens also does just fine with nothing to climb on, in which case it tends to climb upon itself and create a spreading thicket (see photograph above). It can also be kept in a container but requires frequent pruning of its rapidly growing stems.
This dryland ʻāwikiwiki does best when grown in a site that receives full sunlight for all or most of the day. It can tolerate a bit of shading, but shaded plants may not be as silvery (i.e., fuzzy) or flower as often as plants in full sunlight. Once established (after one to two months in the ground), Canavalia pubescens requires little to no watering, and you should avoid overwatering since this can promote stem and root rot. This ʻāwikiwiki can tolerate extreme heat, drought, strong winds, and some salt spray. It will grow in cinder-rich, organic-dominant, and (coralline) sandy soils provided the soil drains water quickly.
As mentioned above, Canavalia pubescens grows quickly and, because it can fix nitrogen, normally does not require nitrogen-containing fertilizers; I never fertilized my ʻāwikiwiki except when I kept them in a pot for an extended period (i.e., over a year), in which case, I applied a balanced controlled-release granular fertilizer every six months. C. pubescens is considered to have a lifespan of ten years or less, although to date, there haven't been any scientific studies to confirm this. Unfortunately, all my C. pubescens have died after a few years because I failed to adequately monitor for and control their many pests.
Pests and Diseases
Canavalia pubescens is attacked by a multitude of pests, all sadly introduced to Hawai‘i in the last 200 years. The most frequent and serious are infestations of lace bugs (see photographs below) and spider mites, which yellow and kill the plant's leaves. Stink bugs and aphids can also sometimes become a problem. And, in moist environments, snails, slugs, and cockroaches may eat the leaves and stems of your ʻāwikiwiki.
Our Pests & Diseases page describes different ways to control/eliminate each of these pests. If the attacks on your ʻāwikiwiki are frequent and severe, you may be tempted to opt for more long-lasting controls like a systemic insecticide and miticide. However, using a systemic insecticide comes with a significant downside. Unfortunately, all the systemic insecticides easily available to the public in Hawai‘i contain imidacloprid which is extremely deadly to bees, making its use a difficult decision: "Do I kill the bees in my neighborhood in order to protect my ʻāwikiwiki?"
Lastly, it's entirely possible that your pest problem gets out of control and your ʻāwikiwiki drops all or most of its leaves. Don't panic! There's a good chance your plant can recover if you immediately start and repeatedly treat the surviving stems with an insecticide and/or miticide.