Last updated:
Last updated: July 30, 2026
Quick answer: In the Phoenix area the single most important seasonal task is changing your irrigation controller, and most landscapes are killed or wasted by leaving it on one setting all year. The Arizona Municipal Water Users Association advises that irrigation schedules should be adjusted at least four times a year. As a reference point for how far apart those settings sit, AMWUA’s July guidance for established plants is roughly: summer grass every 3–4 days, high-water-use shrubs and groundcovers every 6 days, high-water-use trees every 9 days, desert-adapted shrubs and groundcovers every 13 days, desert-adapted trees every 17 days, and cacti and succulents every 21 days. Those intervals stretch out substantially as the weather cools.
Why a Phoenix calendar is really an irrigation calendar
In milder climates a landscape calendar is mostly about planting and pruning. Here, the controller does more damage or more good than anything else you touch. A schedule that is correct in July is wildly wrong in January, and a schedule left on winter settings through June kills plants quickly.
The frequency spread in the July figures above is the thing worth internalising: cacti at roughly every 21 days and summer grass at every 3–4 days are on the same property, in the same heat, needing schedules nearly seven times apart. Any zone that mixes those plant types cannot be watered correctly at any setting. Grouping plants by water need is what makes the calendar workable at all — see our Phoenix irrigation page for how zoning is set up.
The four adjustments
AMWUA’s guidance is to adjust irrigation schedules at least four times a year. In practice those change points track the transitions rather than the calendar quarters.
Spring (as temperatures start climbing). Intervals shorten from their winter settings. This is the adjustment people most often make too late — the first hot stretch arrives before the controller has been touched, and established plants take the damage before anyone notices.
Early summer (the dry, hot run-up). The tightest intervals of the year. This is when the July-style frequencies above apply and when an underperforming system shows every weakness it has.
Monsoon season. Rainfall becomes genuinely significant and irrigation should account for it rather than run through it. A controller with no rain shut-off, running its summer schedule during a wet stretch, is watering a saturated root zone.
Autumn into winter. Intervals lengthen considerably. Cooler air, lower evaporation and shorter days mean established desert plants need far less. Winter over-watering is quieter than summer under-watering but it is just as damaging, particularly where drainage is restricted.
How often should I water new plants?
New plantings are on a different schedule from established ones, and it steps down over roughly two months. AMWUA’s establishment guidance is:
- Weeks 1–2: every 1–2 days in summer; every 3–4 days fall through spring.
- Weeks 3–4: every 3–4 days in summer; every 6–7 days fall through spring.
- Weeks 5–6: every 4–6 days in summer; every 7–10 days fall through spring.
- Weeks 7–8: every 7 days in summer; every 10–14 days fall through spring.
AMWUA also notes that during establishment each irrigation should wet the root ball and one to two inches of the surrounding soil — the point being to encourage roots out of the root ball and into the native soil rather than keeping them in the container shape they arrived in.
The practical consequence is that new plants need their own zone or their own attention for the first couple of months. Putting a new tree on the same schedule as established desert-adapted trees is one of the most common reasons a new planting fails.
Does planting time matter in Phoenix?
Considerably, and the reason is visible in the numbers above. A plant installed at the start of the hot season faces its most demanding establishment period at the least forgiving time of year — every 1–2 days for the first fortnight, with no margin if a cycle is missed or an emitter clogs. The same plant installed in the cooler part of the year establishes on a 3–4 day interval with far more tolerance for error.
That is why so much desert landscape installation is scheduled outside peak summer. It is not that summer planting is impossible; it is that summer planting demands a level of irrigation reliability that many systems do not have.
What else changes through the year?
Check the system before the heat, not during it. The most valuable maintenance visit of the year is the one that happens before peak summer: run every zone, walk every emitter, clear blockages and replace failures. A clogged emitter discovered in July costs a plant; the same emitter found in spring costs nothing.
Reassess after the monsoon. Storms move gravel, silt up basins, and bring down limbs. Reforming watering basins matters because a basin that no longer holds water sends the next irrigation cycle sideways instead of down.
Do not forget winter entirely. Established desert plants need much less water in winter, but they do not need none, and dry winter spells still draw on them.
Watch the soil, not just the schedule. Where caliche restricts drainage, the same schedule produces very different results across one yard. Our Phoenix soil guide covers how to test drainage and what to do where the layer sits shallow.
Frequently asked questions
How many times a year should I change my irrigation schedule in Phoenix? AMWUA advises adjusting irrigation schedules at least four times a year. A single year-round setting is either drowning plants in winter or starving them in summer.
How often should I water desert-adapted trees in July? AMWUA’s July guidance for established desert-adapted trees is roughly once every 17 days. High-water-use trees are closer to once every 9 days.
How often should cacti be watered in summer? AMWUA’s July guidance for established cacti and succulents is about once every 21 days.
How often should I water a summer lawn in Phoenix? AMWUA’s July guidance for summer grass is once every 3–4 days.
How often do new plants need watering? Every 1–2 days in summer for the first two weeks, stepping back to every 3–4 days in weeks 3–4, every 4–6 days in weeks 5–6, and every 7 days by weeks 7–8. Fall through spring the equivalent intervals are 3–4, 6–7, 7–10 and 10–14 days.
How much water should a new plant get? AMWUA advises that each irrigation during establishment should wet the root ball and one to two inches of the surrounding soil.
Can cacti and lawn share an irrigation zone? No. In July their recommended intervals are roughly 21 days and 3–4 days. No single run time is correct for both.
Sources
- Arizona Municipal Water Users Association — landscape watering guidance and monthly schedules: amwua.org
- Arizona Municipal Water Users Association — new and established plant watering schedules: amwua.org/landscaping-with-style