Drip irrigation is planned in rows and bought in metres, and the gap between those two is usually the first surprise: a modest vegetable patch with six beds needs more than fifty metres of line once the headers are counted, and around a hundred and sixty emitters. That matters for two reasons that have nothing to do with the bill. The emitter count sets the flow rate, and the flow rate decides whether your supply and your filter can run the whole patch at once or whether it has to be zoned. This lays the beds out as rows, counts every emitter, and gives you the litres per hour the system has to deliver.
Beds, rows and emitters
One emitter every 30 cm, on every row. The metres add up faster than people expect.
One line per bed for a vegetable patch; two for anything wider than about 1.2 m.
30 cm is standard for vegetables; 20 cm on sandy soil; 45 to 60 cm for shrubs.
Pressure-compensating emitters are usually 2 L/h; some are 1, 4 or 8.
The header runs across the beds at one end, or down the side.
Inline emitter tubing is more per metre than plain tube plus punch-in emitters.
Result
Why the emitter count matters more than the metres
The length of line is what you buy and the emitter count is what the system has to feed, and they are different numbers with different jobs. Six rows of eight metres is forty-eight metres of tubing and a hundred and sixty-two emitters, and it is the second figure that decides whether the installation works: every emitter draws its rated flow, and the supply has to deliver all of them at once.
That total flow is the constraint almost every domestic drip system runs into. A hundred and sixty-two emitters at two litres an hour is three hundred and twenty-four litres an hour, or about five and a half litres a minute. A garden tap feeding through a standard hose and a filter can usually manage that, but add a second patch, or go to four-litre emitters, and it cannot — and the symptom is not a dramatic failure, it is simply that the far end of the last row barely drips.
Spacing is a soil decision, not a product decision
Emitter spacing is about how far water spreads sideways in the soil. In a sandy soil water moves down and barely sideways, so a single emitter wets a narrow cone and the emitters have to be close together — twenty centimetres — for the wet cones to meet. In a clay or a loam, water spreads sideways much more freely and thirty or even forty-five centimetres gives continuous wetting.
Getting this wrong in either direction is visible in the plants. Too wide and each plant sits on its own dry island between wet spots. Too close and you are paying for emitters and flow you do not need, and over-watering, which in a drip system is a slower and more insidious problem than under-watering because nothing runs off to show you.
Row spacing interacts with it. Where plants are in rows, one line per row at the plant spacing is right for vegetables. For a wide bed or for shrubs, the conventional answer is two lines per bed, or a single line with a wider spacing once the plants are established and their roots have spread.
A non-compensating emitter delivers more at the start of a run where the pressure is higher and less at the far end. On a long row, or any slope, that means the first plant is flooded and the last is dry.
Pressure-compensating emitters cost more per emitter and deliver the same flow across a wide pressure range. On a slope of more than a metre or a row longer than about thirty metres, they are the cheaper choice.
Zoning, filtration and the parts that are not line
If the total flow exceeds what the supply and the filter can pass, the answer is zones: split the system so each part runs separately on a timer or a manual valve. Six hundred litres an hour is a working ceiling for a domestic filter and a normal hose, and the figure above tells you how many zones you need. Zoning is not a compromise — it is how every installed system is built, and it makes the difference between a system that works and one that dribbles at the far end.
Filtration is not optional with drip. Emitters have orifices around a millimetre across, and a single grain of sand blocks one permanently. A simple mesh filter at the tap is enough for mains water; a disc filter is better on a rainwater or a bore supply. The pressure reducer is the other essential, because most drip line is rated to about 1.5 bar and mains pressure is frequently three or four times that.
| Part | How many | Why | Skip it? |
|---|---|---|---|
| Header tubing | One run across the beds | Gets water to each row | No |
| Filter | One per system | Emitter orifices are tiny | No |
| Pressure reducer | One per system | Line is rated around 1.5 bar | No |
| End caps or flush valves | One per row | Lets you flush the line out | No |
| Connectors and tees | One per row junction | Joins rows to header | No |
| Timer | One per zone | Automates it | Only if hand-watering |
| Staples or pegs | One per metre or two | Holds the line down | Nice to have |
The irrigation run time figure is the other half of this: once you know the flow the system draws, that tells you how long to run it to deliver the depth the plants need, and whether the soil can take it in one session or needs splitting into cycles.
A worked example
- Line in the bedsSix rows of eight metres is 48 m of line.
- EmittersOne every thirty centimetres is 27 per row, so 162 emitters across the patch.
- FlowAt 2 L/h each the system draws 324 L/h, which is about 5.4 litres a minute and fits through one zone.
- HeaderFive gaps between six beds at 0.9 m is 4.5 m of header.
- The order52.5 m of line at $1.20 is $63 — before the filter, the reducer, the connectors and the timer.
Sixty-three dollars of tubing is the small number. The filter, the pressure reducer, the connectors and a timer typically come to more than the line itself on a system this size, which is why the parts list above is worth pricing before the tubing.
Where the numbers stop being true
Emitter spacing is treated as uniform along each row, which is how the product is sold for inline tubing — the emitters are moulded in at a fixed interval. With punch-in emitters the spacing is yours to choose, and the usual reason to vary it is a heavy feeder at one end of a row or a plant that wants to stay dry.
Nothing here accounts for pressure loss along the run. Long rows, small-diameter tubing and any rise in height all reduce the flow at the far end, and on a row beyond about thirty metres the reduction is enough that the last few emitters under-deliver even with compensation. The practical fixes are a larger-diameter header, or feeding the row from both ends.
The line is assumed to run to the end of each row and stop. Where beds are watered from both ends, or where the rows are laid out as a loop, the header length changes shape entirely, and it is worth sketching the layout before ordering. If the beds themselves are raised rather than at grade, the raised bed figure matters for how much water the bed holds between sessions, and the mulch figure reduces how often you need to run it at all.
Do
- Count the emitters as well as the metres — the flow is what constrains the system.
- Set the spacing from your soil, not from the catalogue.
- Fit a filter and a pressure reducer, whatever the water source.
- Flush the lines at the end of the season before the frost.
- Order end caps, connectors and a few spare emitters with the line.
Avoid
- Assuming a domestic supply will run an unlimited number of emitters at once.
- Using 30 cm spacing on sand, where the wet cones never meet.
- Running drip at mains pressure without a reducer.
- Forgetting the header length when ordering.
- Laying line without a way to flush it out.
How the figures are produced
Rows multiplied by row length gives the line in the beds. Emitters per row is the row length divided by the spacing, rounded up, and total emitters is that times the number of rows. Flow is emitters times the flow per emitter. Header length is the number of gaps between beds multiplied by the bed spacing, and the total to buy adds the two. The zone figure divides total flow by a working ceiling of six hundred litres an hour and rounds up.
Questions people ask
Why so many emitters?
Because they are every thirty centimetres along every row. Six eight-metre rows is forty-eight metres, which at that spacing is a hundred and sixty-two emitters.
Can I run it all at once?
If the total flow is under about six hundred litres an hour, usually yes. Above that, split it into zones and run them in sequence.
What spacing should I use?
Thirty centimetres on loam, twenty on sand, forty-five to sixty for established shrubs. It is about how far water spreads sideways in your soil.
Do I need pressure-compensating emitters?
On flat ground with short rows, no. On a slope, or on rows over about thirty metres, yes — otherwise the first plant is flooded and the last is dry.
Can I use a soaker hose instead?
Yes, and it is cheaper and simpler, but it delivers unevenly, it cannot be spaced and it blocks more easily. Drip is the better system; a soaker is the better first step.
How do I stop it blocking?
Filter the water, flush the lines at the end of each season, and do not leave the system pressurised over winter with water in it.