Plant Selection and Horticulture
What the exam tests
Plant Selection and Horticulture tests whether you can choose and specify plants that survive the site, not just look good on a plan. Questions cover plant identification, climate and soil adaptation, native and invasive species, irrigation zones, planting details, establishment, pruning, fertilization, and integrated pest management. Hawaii's microclimates-windward rainforest, leeward dryland, upland cool, coastal salt-make 'right plant, right place' a technical, not sloganeering, decision.
Core rules
- Match plant to microclimate: rainfall, sun, wind, salt spray, temperature, and soil depth. A windward Hilo site and a leeward Kona site are not interchangeable.
- Know the categories: endemic (found only in Hawaii), indigenous (native to Hawaii and elsewhere), Polynesian introduced (e.g., kukui, ti, hala), and introduced/invasive.
- Avoid known invasives such as miconia, albizia, strawberry guava, and fountain grass; check the Hawaii noxious weed list and county planting restrictions.
- Test soil or at least observe drainage. Volcanic andisols often fix phosphorus and can be acidic; coral-derived sands are alkaline and drain quickly.
- Specify the planting hole, root flare, mulch ring, staking only if needed, and irrigation separate from establishment water.
Worked example
A 6-ft-wide planting strip between sidewalk and curb in Kailua, windward Oahu: full sun, salt spray, no irrigation after establishment, and pedestrian clearance required. Reasoning: reject plants that need constant water or reach into the walkway. Choose low, salt-tolerant, wind-tolerant groundcovers and shrubs such as ʻilima or beach naupaka, set back from the curb, with a 3-in mulch layer and no tree in the strip. Confirm mature spread and sight-line clearance. If irrigation is required only for establishment, specify a temporary drip line, not permanent spray heads.
Traps
- Planting a tree too deep or burying the root flare.
- Using fertilizer at planting to 'push' growth; it can burn roots.
- Mixing high-water and low-water plants in one irrigation zone.
- Calling a plant 'native' when it is only Polynesian introduced or naturalized.
- Ignoring mature size, root barriers, and utility clearance.
- Specifying invasive species because they are cheap or fast-growing.