Landscape Design and Plant Selection for a Coastal Garden
A client wants to landscape a 500 m² coastal garden in a region with sandy soil, high winds, salt spray, and a pH of 8.0. The garden is 100 m from the sea. The client wants low-maintenance plants, some colorful flowers, and a small lawn area for children to play. The site is relatively flat, with full sun exposure. The average annual rainfall is 600 mm, mostly in winter. The client has a budget of $5000 for plants and materials. The soil is low in organic matter (0.5%) and drains rapidly. The client is willing to install an irrigation system but prefers to minimize water use. The garden will be used year-round. The client has expressed interest in native plants but is open to other suitable species. There is a prevailing wind from the sea.
1. Discuss the challenges of this site and propose a planting plan that addresses them, including soil improvement, plant selection, and irrigation strategy.
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Challenges: sandy soil with low water and nutrient retention, high pH limiting nutrient availability (especially iron, manganese, zinc), salt spray and wind causing desiccation and leaf burn, and high evaporation. The lawn area for children needs to be tough and salt-tolerant. Soil improvement: incorporate organic matter (compost) at 5-10 cm depth over the entire garden, and in lawn area, add 10 cm. This improves water holding capacity and nutrient exchange. For pH, elemental sulfur can be added but may be impractical; better to choose pH-tolerant plants. Plant selection: choose salt-tolerant, wind-resistant species. For colorful flowers: Lavandula angustifolia (lavender), Armeria maritima (sea thrift), Echium vulgare (viper's bugloss), and Osteospermum (African daisy). For shrubs: Griselinia littoralis, Pittosporum crassifolium, and Hebe species. For native plants: if in a suitable region, consider Arctostaphylos (manzanita) or Ceanothus, but check local native species. For lawn, use salt-tolerant grass like seashore paspalum (Paspalum vaginatum) or tall fescue with endophytes. Irrigation: install drip irrigation with a controller and soil moisture sensor, group plants by water needs (hydrozones). Use mulch (e.g., bark or gravel) to reduce evaporation and weed growth. Windbreaks: plant a hedge of salt-tolerant shrubs on the windward side to reduce wind speed and salt spray. This also creates a microclimate. Budget: allocate for compost, plants, irrigation, and mulch. Prioritize windbreak and soil improvement. Maintenance: low-maintenance plants, but initial watering until established. Avoid plants sensitive to salt and high pH.
2. Explain how you would schedule irrigation for the different hydrozones and how you would monitor plant health and adjust the plan over the first year.
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Irrigation scheduling: For the lawn zone, which has highest water demand, irrigate deeply and infrequently to encourage deep roots. In summer, apply 25-30 mm per week, split into two applications. Use a rain sensor and soil moisture sensor to avoid overwatering. For the flower and shrub zones, use drip irrigation with emitters rated at 2-4 L/h. Water newly planted shrubs and flowers every 2-3 days for the first month, then reduce to weekly. For native and drought-tolerant plants, water only during establishment (first 3 months) and then only in severe drought. Group plants by water need: high (lawn), medium (flowers, some shrubs), low (native, lavender). Use separate valves. Monitor plant health: weekly inspections for signs of salt burn (leaf tip necrosis), wilting, or nutrient deficiency (yellowing). Test soil moisture with a probe. Adjust irrigation run times based on observations. After the first year, evaluate plant survival and growth, and replace any that fail. Also, check soil pH and organic matter annually. Keep a garden journal. If salt accumulation is visible (white crust), leach with extra water. Consider using compost tea or organic fertilizers to improve soil health. Communicate with the client about maintenance tasks.