HI Landscape common mistakes
HI Landscape · Understand the traps and how to avoid them.
Selecting plants by mature height and flower colour only, without checking the site's hardiness zone, exposure, soil pH, and drainage class before committing to a planting plan.
Candidates study plant lists as isolated facts and treat design as an aesthetic exercise, so they skip the cross-check between species tolerances and the site conditions given in the scenario.
What to do instead
Build a habit of writing a four-line site constraint summary (zone, light, soil pH, drainage/moisture) before evaluating any species, then eliminate candidates that fail any single constraint. Practise with species that share a look but differ in tolerance, such as sun versus shade perennials or acid-loving versus lime-tolerant shrubs.
Confusing the design concept and schematic design phases with construction documentation, delivering detailed layouts and material specifications when the question asks what belongs in the earlier phase.
The phases are learned as a list rather than as a sequence of deliverables and decision types, so the boundaries blur under time pressure.
What to do instead
Memorise a one-line deliverable for each phase (programming, concept, schematic, design development, construction documents, construction administration) and a one-line client approval tied to each. When a question names a phase, ask what decision is being locked in at that point, not how detailed the drawing looks.
Calculating hardscape quantities from plan dimensions alone, ignoring base depth, compaction, over-excavation, and waste allowance, then reporting a material volume that is short on the estimate.
Candidates treat the visible paver area as the quantity and forget that base aggregate and bedding sand are three-dimensional, and that compaction reduces loose volume.
What to do instead
Always compute in three steps: excavation volume (area times total section depth), compacted base volume converted to loose volume via a bulking factor, and a stated waste percentage. Write the section layers out explicitly before multiplying, and sanity-check that base volume exceeds paver volume for typical pedestrian sections.
Sizing irrigation zones by counting heads rather than by matching precipitation rates and available flow and pressure, producing zones that mist, fog, or starve the farthest heads.
Head-count rules of thumb are easier to remember than hydraulic limits, and candidates rarely check that matched precipitation rate is the design goal.
What to do instead
For each zone, verify three things explicitly: total flow at design pressure stays under the available supply, all heads on the zone have the same precipitation rate (or are compensated by nozzle selection), and pressure loss from length, elevation, and fittings is accounted for. Practise converting gallons per minute to inches per hour for a given head spacing.
Reading spot elevations but not contour intervals, so slope direction and drainage patterns are misread and water is shown flowing toward a building or a flat pad.
Spot elevations are concrete numbers while contours require spatial interpolation, and candidates default to the easier cue.
What to do instead
Before answering, state the contour interval, mark the high and low points, and draw flow arrows perpendicular to contours. Then check every proposed surface falls away from structures at the minimum slope and that swales have a positive grade to an outlet.
Producing an estimate that omits general conditions, contingency, permits, and mobilization, so the total looks competitive but cannot cover the actual job.
Line-item pricing is what gets practised; soft costs and indirect costs are abstract and easy to forget when the question focuses on quantities.
What to do instead
Use a fixed estimate skeleton every time: direct labour, materials, equipment, subcontractors, general conditions, contingency, overhead and profit, then taxes and permits. For any estimate question, check whether each category is represented before summing.
Treating safety questions as common sense, missing the specific trigger thresholds for trench shoring, excavation access, and utility locating before digging.
Candidates rely on general awareness instead of the numeric thresholds and procedural sequences that the exam tests, and they overlook call-before-you-dig timelines.
What to do instead
Memorise the trigger depths and clearance distances that apply in your jurisdiction for shoring, sloping, and ladder access, and the locate-request lead time before excavation. For each scenario, ask what must happen before the first shovel enters the ground, and what protective system is required at the stated depth.
Ignoring microclimate and existing site features such as mature tree root zones, prevailing winter wind, and reflected heat from paving when placing planting beds.
Design is done on a blank plan, and candidates do not translate site inventory notes into planting decisions.
What to do instead
Convert each site inventory item into a design constraint before laying out beds: root protection zones become no-dig areas, windward edges need shelter species, and south- or west-facing hardscape needs heat- and drought-tolerant selections. State the constraint-to-response link explicitly in your answer.
Answering drainage questions with a single pipe or drain without checking that the outlet is legal and lower than the inlet, and without verifying the pipe slope is adequate.
Candidates focus on collecting water and stop before the discharge point, and they do not check grade against the minimum slope for the pipe diameter.
What to do instead
For every drainage answer, trace the full path: collection, conveyance, storage or infiltration, and a legal point of discharge. Verify invert elevations drop along the run and that slope meets the minimum for the pipe size, then confirm discharge does not create a nuisance or violate the local stormwater rule.
Writing project schedules and specifications that leave out sequencing dependencies and inspection hold points, so the plan reads as a list of tasks rather than a buildable sequence.
Candidates list activities in the order they occur to them, without linking predecessors, curing times, or required inspections that gate the next trade.
What to do instead
For any schedule question, identify the predecessor for each activity, note cure or settle times that force waiting, and mark the inspection hold points that must clear before the next step. If a proposed sequence has two trades in the same place at once, treat it as an error to be resolved.