Drip Schedule on Caliche
A 4,800-square-foot common area in Henderson was planted in August with 15-gallon trees and 1-gallon shrubs on a 6% slope. The irrigation is drip: two 2.0-gph emitters per tree, one per shrub. The controller runs 12 minutes per day, three days per week. Below 6 inches of imported topsoil is an 8-inch caliche layer. By October, 40% of the shrubs and 6 of 30 trees are dead or declining. Water ponds at the bottom of the slope, while mid-slope areas are dry. The owner says the contractor installed defective plants and demands replacement at no cost. The contractor's foreman recalls that the controller was set to the grower's nursery schedule at planting, and no one adjusted it. There are no soil tests, no as-built irrigation drawing, and no written maintenance turnover. The contract includes a one-year plant warranty but says the owner is responsible for watering after acceptance.
1. Diagnose the most likely causes of the plant loss and the dry/wet pattern. Support each cause with a number or site fact.
Read the worked answer
The numbers point to a water-delivery failure, not bad plants. Each tree receives two 2.0-gph emitters, or 4 gph. At 12 minutes per day, three days per week, that is 36 minutes, or 0.6 hour, per week: 4 gph x 0.6 hr = 2.4 gallons per tree per week. A 15-gallon tree planted in August in Henderson needs substantially more than that to establish, especially in full sun. Each shrub gets one 2.0-gph emitter and therefore only 1.2 gallons per week. The schedule was a nursery schedule and was never adjusted.
The caliche matters too. An 8-inch caliche layer beneath only 6 inches of topsoil restricts downward drainage. Water applied faster than it can infiltrate ponds at the bottom of the 6% slope and runs off, while mid-slope emitters may be clogged, misaligned, or applying water that moves downslope before it soaks in. The result is a bathtub at the low end and dry root zones mid-slope. Planting into a shallow topsoil layer over caliche can also create a perched water table and restrict root growth. The pattern is hydraulic and soil-related, not a plant-quality defect.
2. Write a corrective plan for irrigation and planting that addresses the caliche and the slope.
Read the worked answer
Correct the soil and water system before replacing plants. First, verify static pressure and flush the drip lines; install pressure-compensating emitters so the slope does not starve the high points. Second, test infiltration and dig test holes to confirm the caliche depth. Break through the caliche with auger holes or planting pits that drain, or plant on raised mounds with a designed outlet; do not simply enlarge the topsoil pocket over an impermeable layer. Set trees with the root flare at grade and form a watering basin on the uphill side.
Third, split the site into hydrozones: trees, shrubs, and slope areas need different run times. For establishment, a reasonable starting point is cycle-and-soak: several shorter cycles with soak time between, three days per week, then adjust based on moisture readings. A 15-gallon tree with four 2.0-gph emitters run about 75 minutes per week would receive roughly 10 gallons, far closer to establishment need than 2.4 gallons. Fourth, add mulch and check for runoff at the bottom of the slope. Replace dead plants only after the water and drainage corrections are working.
3. What project records would have reduced the dispute, and which specific records should the contractor produce now?
Read the worked answer
Good records would have separated design, installation, and maintenance. The file should contain the approved planting and irrigation plans, soil and infiltration test results, irrigation as-builts with emitter sizes and zones, the controller schedule at turnover, photos at installation, daily logs, water-pressure readings, and a signed maintenance turnover showing the owner accepted watering responsibility. The contract's one-year warranty is not automatic replacement coverage if decline is caused by owner maintenance or a design condition the owner approved.
Now the contractor should produce the controller schedule, any photos showing planting depth and basins, purchase invoices showing plant size and condition, and the contract and warranty language. It should also document current soil moisture and emitter flow at several points on the slope. That evidence supports the argument that the plants were installed per the approved plan and that the failure is a water-management and caliche-drainage issue. Without those records, the contractor is left arguing from memory against the owner's photographs.