Garden Oracle / Drought and Heat Tolerant Gardening / Tucson - Phoenix - Arizona - California

Growing Guaiacum coulteri:

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Form: A shrub that may eventually grow into a tree.
Lifespan: Possibly up to 1000 years.
Leaf retention: Evergreen.
Growth rate: Very slow, likely less than 1" (2.5cm) a year.
Mature Size: 5-13' (1.5-4m) high and as wide, over 30' (9m) in its native environment if left undisturbed.
Flowers: Five blue to purplish, paddle-shaped petals, surrounding yellow anthers. The flowers occur both singly and in small clusters.
Bloom: A primary bloom occurs mid-spring with sporadic blooming throughout the rest of spring and summer.
Fruit: A seed capsule with 2-5 wings and lobes, each lobe containing a seed with a bright red coating (aril). The capsule, initially green, ages to yellowish orange, possibly red-brown.
Leaves: Small, green, oval, nearly round to elongated leaflets, sometimes with a pointed tip, grouped in pairs of 2-6. With insufficient water, the leaflets rotate their stems in high temperatures so that they catch the sun on their edges to minimize heat stress.
Stems: Grey, furrowed, crooked, no thorns, with short spur shoots for leaf attachment. The branches on top of the shrub can appear sparsely leaved when the leaflets rotate edge-on to the sun with insufficient water. The wood of the five Guaiacum species is called lignum vitae, is one of the hardest, toughest, densest woods known, and is heavier than water.
Roots: This plant forms a taproot.
Wildlife: The flowers attract bees and butterflies. The seeds, when present, attract birds and small mammals. The leaves are browsed by deer and livestock.
Toxic / Danger: None.
Origin: Western Mexico outside of Baja California, including regions along the Pacific Coast; and Guatemala.

Cultivation and Uses
USDA hardiness zones: 9b-11. This plant experiences freeze damage below 25°F (-3.9C).
Heat tolerant: Yes.
Drought tolerant: Yes.
Sun: Full sun.
Planting: Locate this plant in full all day sun, in very well draining soil. It will grow in a container.
Soil: Very well drained, gravelly, low in organic content. Fertilize with composted manure in winter to speed growth. This plant is salt tolerant.
Water after becoming established: Every 1-2 weeks in warm months. Weekly watering speeds growth. Every 3-4 weeks in winter.
Mulch: Not necessary.
Prune: Trim only lightly to shape or not at all. This plant grows very slowly. Remove any tall weeds by hand that are growing within 2' (60cm), and under the canopy, of this plant.
Litter: Low to none.
Propagation: Seed, less than one month old, with the red coating (aril) removed, soaked until swelled in water, and placed in a gel or agar medium. Dried seed over one month old are not viable.
Uses: Ornamental.

This plant is a member of the Creosote Bush family (Zygophyllaceae).
Guaiacum sanctum: Lignum Vitae / Holywood, a nearly identical, more widespread species prized for the healing properties of its resin and bark, has moderate water needs, tolerates shade, can be mistaken for this plant and may hybridize with it where their ranges overlap.
The members of this genus have been harvested to endangered status in most of their native regions.
The slow growth of this plant does not compete well with taller, faster growing species.

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Guaiacum: Guayacan flower

Guaiacum: Guayacan seed capsule

Guaiacum: Guayacan leaves folded
These leaflets rotate to minimize light exposure
during the heat of the day when water is insufficient.

Guaiacum: Guayacan

Latest update: January, 2024
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