Sizing a drip irrigation system involves calculating the water needs of your plants, determining the appropriate components, and ensuring your water source can supply enough flow and pressure.
Sizing is crucial for efficient watering, ensuring each plant receives the right amount of water directly at the root zone, minimizing waste, and promoting healthy growth. Key factors include understanding plant types, soil conditions, and your water source's capacity.
Key Factors in Drip System Sizing
Proper sizing depends on several interconnected elements:
- Plant Water Requirements: Different plants need varying amounts of water. This is perhaps the most critical factor in determining how many emitters you need and their flow rate.
- Soil Type: Soil affects how quickly water is absorbed and spreads. Sandy soils absorb water faster but don't spread it widely, potentially requiring more emitters per plant. Clay soils absorb slower but spread water wider, possibly needing fewer emitters.
- Water Source Capacity: The available water pressure and flow rate (gallons per minute - GPM) from your faucet, well, or pump are essential. Your total system's demand cannot exceed this capacity.
- Pressure Regulation: Drip systems operate at low pressure (typically 10-30 PSI), much lower than standard household pressure. A pressure regulator is necessary.
- Zoning: Large systems often need to be divided into zones to manage the total flow rate required at any one time, ensuring pressure remains adequate throughout the system.
Sizing Based on Plant Type & Size
Understanding the water needs of specific plants is fundamental. For shrubs and trees, the size of the plant dictates the number and flow rate of emitters required to adequately cover the root zone.
Here are typical emitter requirements based on plant size, using information from the provided reference:
- Shrubs taller than 5 feet: Need three one-gallon emitters.
- Trees between 5 and 10 feet tall: Require two to three 2-gallon emitters.
- Trees between 10 and 15 feet tall: Need two 4-gallon emitters.
- Trees between 15 and 25 feet tall: Should use four 4-gallon emitters.
This demonstrates how the size and type of plant directly influence the system's design, specifically the emitter selection and placement.
Emitter Requirements Table
| Plant Type & Size | Emitter Quantity | Emitter Flow Rate (GPH) | Total Flow Per Plant (GPH) |
|---|---|---|---|
| Shrub (> 5 ft) | 3 | 1 | 3 |
| Tree (5-10 ft) | 2-3 | 2 | 4-6 |
| Tree (10-15 ft) | 2 | 4 | 8 |
| Tree (15-25 ft) | 4 | 4 | 16 |
Note: GPH stands for Gallons Per Hour.
For groundcovers or densely planted areas, drip line or soaker tubing with integrated emitters spaced every 12-18 inches is often used instead of individual emitters.
Calculating System Capacity
Once you've determined the emitter needs for all plants in a zone, sum up the total GPH requirement for that zone.
- Example: A zone with 5 shrubs (>5ft), 2 trees (6ft), and 1 tree (12ft).
- Shrubs: 5 plants 3 emitters/plant 1 GPH/emitter = 15 GPH
- Trees (6ft): 2 plants 3 emitters/plant 2 GPH/emitter = 12 GPH
- Tree (12ft): 1 plant 2 emitters/plant 4 GPH/emitter = 8 GPH
- Total Zone Demand: 15 + 12 + 8 = 35 GPH.
Convert GPH to GPM (GPH / 60) to compare against your water source's capacity. 35 GPH is approximately 0.58 GPM, well within the capacity of a typical residential water source.
You must ensure the total GPM of any single zone does not exceed your water source's GPM capacity, while operating within the appropriate pressure range (after the regulator). If your total demand exceeds your source's capacity, divide the system into multiple zones, each controlled by a separate valve.
Additional Sizing Considerations
- Tubing Size: Use appropriate poly tubing sizes (e.g., 1/2" or 3/4") for main lines and smaller (e.g., 1/4") tubing for connecting emitters to plants. Sizing depends on the length of runs and flow rate to minimize pressure loss.
- Filters: Always include a filter (e.g., 150-200 mesh) to prevent clogs in emitters, a common issue if not properly sized and maintained.
- System Layout: Plan the layout to minimize tubing runs and ensure efficient water delivery to all plants.
By considering these factors and using guidelines like the plant-based emitter sizing, you can effectively size a drip irrigation system for optimal performance.
