Crop irrigation · Row crop
Drip Irrigation for Onions
Onion is the crop that exposes everything: plants 10–15cm apart mean the emitters have to be that close, and a short 3–4 month season means the system's uniformity is judged on every single bulb. Here's the setup.
Onion's irrigation requirements
Onion sits in an awkward middle for watering: it needs consistent moisture — irregular supply is the classic cause of split, layered or small bulbs — but its roots are shallow and it dislikes waterlogging, which rots the bulb. The pattern that works is steady, moderate, frequent application to the root zone, which is exactly what drip does. The density is the catch: at 10–15cm in-row spacing, you need emitters at 10–15cm and usually two to three lines per bed, which is the highest emitter count of the common vegetable crops.
Drip tape is the usual answer
Getting 10–15cm emitters on multi-season drip lines is possible but costs more per metre — for a 3–4 month crop, the economics usually favour drip tape: cheap per metre at the dense spacings, and its single-season life matches the crop. The rule of thumb: tape for a single intensive onion season; durable lines if you run onions repeatedly on the same beds or mix crops across a long year. The comparison covers the arithmetic.
The system setup
| Parameter | Typical specification | Why |
|---|---|---|
| Plant spacing | 10–15cm in-row, beds 1.0–1.2m | The standard for common Kenyan onion varieties |
| Lines per bed | 2–3 (3 is common at the densest spacings) | Covers the full bed with continuous wetting |
| Emitter spacing | 10–15cm (tape), 20cm on lines for wider spacings | At or below the plant spacing — a 30cm emitter on a 12cm planting wets every other plant |
| Emitter flow | 1.6–2.2 L/h is plenty at this density | The total per metre of line is what matters; keep run times short |
| Season | ~3–4 months (transplant → harvest) | Single-season equipment is usually right |
| Filtration | The most critical of the vegetable crops — see below | Dense fine emitters + a short season = no time to recover from clogs |
Filtration — the onion system's life support
Onion has the highest emitter density of the common crops, so a partially clogged line ends that show up fast and can't be ignored for "next season" — the season is over in 12 weeks. The filter is sized for the system's full flow, matched to the source (disc for borehole/clean tank; sand + disc for dam/river), and the flush routine is non-negotiable: open the line ends on a schedule, because a 10cm-emitter line holds its sediment where it blocks the smallest orifices. Details in the filtration guide.
Scheduling around the bulbing period
- Establishment: frequent light runs while the transplants take — shallow roots, no forgiveness.
- Vegetative growth: steady moderate supply; this builds the neck that will hold the bulb.
- Bulbing (the critical period): the biggest water demand of the season, and the one where inconsistency becomes small or split bulbs. Keep the supply even through it — no drying-out, no waterlogging.
- Maturation: taper off in the final weeks to let the tops down and the bulbs cure — a sharp cut at the right time is what protects storage life. This last taper is where too much drip costs money: wet bulbs don't store.
Common installation mistakes
- Emitter spacing set from "the drip line we had" rather than the planting — a 20cm emitter on a 10cm onion is an alternating-wet row, visible as size variation at harvest.
- Tape laid over a rough bed — the thin membrane punctures on stones and debris; smooth the bed first.
- Waterlogging from over-irrigation on clay — the bulbing period is a demand peak, not a "get it soaking" signal; the schedule stays moderate and frequent.
- No flush points — on a dense-emitter system, the end rows block first and the harvest shows it.
Cost considerations
Onion is at the high end of the vegetable cost band because of the line count (2–3 lines per bed, dense emitters) — see the cost guide for the market ranges. Against that, the crop's value and the market's intolerance of size variation are exactly what uniform drip supply buys.
Related reading
FAQ
Onion drip questions
How many drip lines per bed for onions?
Two to three, depending on the in-row spacing — three is common at 10–12cm plantings, two at the wider end. The lines run the bed with 10–15cm emitters (drip tape is the usual choice). The goal is continuous wetting across the full bed width.
Is drip tape or drip lines better for onions?
For a single 3–4 month onion season, tape usually wins on cost per season at the dense emitters onions need. If you grow onions repeatedly on the same beds across the year, durable lines start to compete on lifetime cost. The comparison guide has the full arithmetic.
How often should onions be watered with drip?
Frequently, in moderate amounts — often daily in the warm season, with short runs. The bulbing period is the peak; keep it even through there. In the final maturation weeks, taper the supply to let the bulbs cure. The starting schedule comes from your soil type — the design works it out.
Why do some onion rows come out small on a drip system?
Usually one of three things: emitters not dense enough for the planting (alternating wet/dry plants), a partially blocked line (the affected row lags), or pressure variation along the line (the far end under-delivers). All three are design/filtration issues, not crop issues — the common problems guide walks the diagnosis.
Where do you install onion irrigation?
Across the onion zones — from the highlands to the Rift Valley and the eastern counties where dry-season onion is the play. See the locations page; send your bed count and we'll quote the line count properly.
Onion season planning?
Send your planting layout — we'll fix the tape or lines, spacing and flush plan before the season does it for you.