It is widely grown as a shade tree to shelter coffee plantations and for shade and forage for cattle; it also improves soil fertility by nitrogen fixation. Guanacaste is in USDA Growth Zones 10-12.
The wood is reddish-brown, lightweight (density 0.340.6 g/cm³) and water-resistant; it is used to make items such as doors, windows, furniture, cabinets, and for shipbuilding. The town of La Cruz de Huanacaxtle in Nayarit (Mexico) derives its name from the fact that a cross used to stand there made of Guanacaste wood.
While the seed pods are still green, they are harvested and the seeds eaten boiled in Mexico. Healthy Guanacaste trees generate massive, nearly annual crops of seeds. The attractive seeds are used in Costa Rica to make jewelry. These seeds demonstrate germination rates of nearly 100%. Guanacaste seedlings then grow rapidly, often reaching over one meter in height in their first year of life. These aggressive reproductive characteristics might be beneficially exploited in reforestation projects; on the other hand, the plant is considered an invasive species in some places. Its roots are strong and those of large trees may damage nearby structures.
Guanacaste is a medium-sized to large tree growing to 2535 m tall, with a trunk up to 3.5 m diameter. Unusual in a tree of these proportions, buttresses are completely lacking. The bark is light gray, with prominent dark reddish-brown vertical fissures. In young trees, these fissures are closer together and their confluence lends a characteristic reddish hue to the bark of Guanacaste saplings. Older specimens often present broken, chipped or scarred bark.
The crown is broad and widely spreading. The height at which branches first occur along the trunk - as well as overall tree shape - vary considerably among individuals and are habitat-dependent characteristics. Frequently, Guanacaste trees grow as single specimens in a sunny pasture. Under these conditions, massive, extended, horizontal limbs emerge low on the boles, forming giant, hemispherical, widely spreading crowns. In the forest (where competition for light is intense), trees tend to become taller and branching occurs at a higher level. Tree forms then become somewhat narrower, though crowns are still rounded and hemispherical shapes are maintained by those that have reached the canopy.
The alternate leaves are bipinnate compound, 1540 cm long and 17 cm broad with a 26 cm petiole bearing 415 pairs of pinnae, each pinna with 4070 leaflets; the leaflets are slender oblong, 815 mm long by 2-4 mm wide. Near its base, the twiggy petiole bares a small, raised, oval gland. The leaves are confined to the outer shell of the crown, yet they are plentiful enough to make it moderately dense and green. Guanacaste is evergreen, or briefly deciduous for 12 months during the dry season. Most foliage is shed in December, at the start of the dry season. In late February, a growth surge is initiated that re-establishes a fresh, thick crown by April.
Concurrent with leaves' renewal is the appearance of globular inflorescences (3 cm) in the axils of the new leaves. Supported by a long pedestal (4 cm), each spherical white head - composed of about fifty individual flowers - sports thousands of thin, filamentous stamens as its major feature. The blossoms themselves each consist of about twenty stamens and a single pistil, bound together at the base by a short, green, tubular corolla and an even shorter calyx, just 5 mm long altogether. Guanacaste flowers are very fragrant and during intense flowering periods their odor permeates the air for many meters in all directions.
Surprisingly, no obvious fruiting activity immediately follows the decline of the blossom. Rather, nine or ten months pass before small, green pods first appear high in the crown by December. They reach full size by February and finally begin to ripen in March - a full year after flowering ceased.
Guanacaste fruits are large (712 cm diameter) glossy dark brown indehiscent and spirally organized pods, shaped like orbicular disks. Their shape suggests the usual Mimosoideae fruit - a long, narrow, flattened pod - taken and wound around an axis perpendicular to its plane. Made of thick, soft tissue with a leathery feel, the pods contain 8-20 radially arranged seeds, 14.517.5 mm long, 7.811.2 mm wide, and 6.27.2 mm thick and weighing about 1 g. Guanacaste seeds are brown and marked with a conspicuous light brown or orange ring. They are also very hard - resembling small stones rather than tree seeds in their strength and durability. In order for germination to occur, the hard seed coat must be broken to enable water to reach the embryo. Otherwise, they will lie dormant indefinitely. Fruit ripening last from March to April, as the green pods turn brown in the Guanacaste crown and are slowly shed. Vigorous trees will produce large crops on a nearly-annual basis. In June, Guanacaste seedlings can already be seen, germinating in the moist soil of the early rainy season