Saguaro
One tall trunk; arms start well up
Southern Arizona, Sonora and a sliver of California
40–50 ft; record 78 ft
Saguaro Cactus Age Chart
How old a saguaro is by its height. Seven saguaros drawn to scale from 10 to 200 years, average growth at three Sonoran Desert sites, and how the plant survives drought, feeds bats and houses owls.
Contents
- 1Two hundred years of growth
- 2Estimating age from height
- 3Life milestones
- 4Life begins in the shade
- 5Built for drought
- 6Blooms that open at night
- 7A saguaro’s year
- 8A desert apartment block
- 9Saguaros and their look-alikes
- 10Only in the Sonoran Desert
- 11Planting and care
- 12Law and threats
- Sources and notes
1.Two hundred years of growth
The same plant at ten ages, drawn to one scale beside a 5′9″ person. Heights follow the average growth at a typical Tucson-area site. Drag the slider or press play.
Figure 2. Left scale: feet; right scale: metres.Circle: close-up of a plant too small to see at this scale.
50 years old
| Height | 6.9 ft 2.1 m tall, typical site |
|---|---|
| Arms | 0 usual range at this age |
| Weight | ~550 lb trunk alone, at ~80 lb per foot (rough) |
050100150200
Milestones by this age
- Seed sprouts Year 0 (reached)
- 1–1½ in tall 10 yrs (reached)
- About 3 ft ~40 yrs (reached)
- First flowers 35–65 yrs (possible now)
- First arm 50–100 yrs (possible now)
- Adult ~125 yrs
- Old age 150–200+
Heights to 150 years are averages from Hodge (1991). Older plants are rough estimates, and any one saguaro can be much taller or shorter.
2.Estimating age from height
Enter a saguaro’s height and the kind of site it grows on. The estimate reads the age off measured average growth curves for three sites with different rainfall.
Stand back and compare the cactus with a person or a doorway (about 6½–7 ft). Measure to the top of the main stem, not an arm.
Estimated age
Wetter site~70 yrs
Typical site~90 yrs
Drier site~115 yrs
About 90 years
Likely range: 80–100 years, taken half-way to the next wetter and drier growth curves, because rainfall varies even within one site.
Wetter site~70 yrsTypical site~90 yrsDrier site~115 yrsRule of thumb, typical siteAge ≈ 30 + 3.5 × (height in ft − 2)20.0 ft → 30 + 3.5 × 18.0 ≈ 93 years.
There is no exact way to age a wild saguaro. Growth swings with rainfall, soil, frost and slope, so treat these as rough estimates, not birth certificates.
Average height by age at three sites
Wetter · Saguaro NP East · ~12 in rain/yrTypical · Saguaro NP West · ~10 inDrier · Organ Pipe NM · ~7.5 inBrass pin: your 20.0 ft saguaro ≈ 90 years on the typical curve
Figure 3. Hover over or tap the chart for the measured heights. More rain means faster growth: by 50 a saguaro averages about 12 ft at the wetter site but under 3 ft at the drier one. Data: Hodge (1991), via the Arizona-Sonora Desert Museum.
Show the saguaro age by height data table
| Site | 10 yrs | 20 yrs | 30 yrs | 40 yrs | 50 yrs | 75 yrs | 100 yrs | 125 yrs | 150 yrs |
|---|---|---|---|---|---|---|---|---|---|
| Wetter | 2.7 in | 18 in | 4.1 ft | 7.9 ft | 12.3 ft | 22.5 ft | 30.4 ft | 36.8 ft | 41.8 ft |
| Typical | 1.5 in | 8 in | 1.9 ft | 4.0 ft | 6.9 ft | 15.9 ft | 24.1 ft | 30.3 ft | 35.1 ft |
| Drier | 1 in | 4 in | 11 in | 1.8 ft | 2.9 ft | 8.1 ft | 15.9 ft | 22.8 ft | 28.5 ft |
| Growth per year, typical | 0.15 in | 0.66 in | 1.5 in | 2.5 in | 3.5 in | 4.3 in | 3.9 in | 3.0 in | 2.3 in |
| Flowers | Usually at least 35 years old; the first blooms come at about 8 ft. |
|---|---|
| Arms | A first arm appears at about 50–100 years; many arms usually means 125+. |
| Under 2 ft | Probably 10–30 years old, often in the shade of a nurse tree. |
| ~4 in a year | The most a saguaro adds, even in its fastest years. |
3.Life milestones
The age ranges overlap because every plant runs on its own clock. Rain-starved saguaros reach each stage later, and some never grow an arm.
Riskiest years 0–40
First flowers 35–65
First arm appears 50–100
Average lifespan 150–175
A few live 200+ 175–200+
Figure 4. Age ranges for each stage, in years.
Year 0
Seed sprouts
days after a summer rain, in a nurse tree’s shade
10 yrs
1–1½ in tall
tiny, spiny and easy to miss; most seedlings die
~40 yrs
About 3 ft
past the riskiest years; few die from here on
35–65 yrs
First flowers
at about 8 ft tall (the Park Service says from ~35 years)
50–100 yrs
First arm
later where rain is scarce; some never branch
~125 yrs
Adult
full size, several arms, often 30 ft or more
150–200+
Old age
average life 150–175 years; a few top 200 and 45–50 ft
4.Life begins in the shade
A seed sprouts days after a summer rain, and the seedlings that live are usually sheltered by a nurse tree such as a palo verde or mesquite, which shades them from sun and frost and hides them from hungry animals.
| 20–40 million | seeds a saguaro may make in its lifetime |
|---|---|
| 1 or 2 | of them, perhaps, ever become adults |
| 1–1½ in | a typical height at age 10: easy to miss |
Most seedlings die in their first years. After about 40, when a saguaro is around 3 ft tall, few die from here on.
5.Built for drought
Slice through the stem and you find an accordion of pleats wrapped round a ring of woody rods. Switch between a stem after a soaking rain and the same stem in a long drought.
Pleats swell, the skin smooths outThe stem fattens as it soaks up water
Figure 6. Stem cross-sections, both drawn at the same scale.
- Pleats expand to store water and fold in as it is used.
- Waxy skin seals the water in.
- Spongy flesh is 90% or more water by weight.
- Woody ribs, 13–20 rods in a ring, are the skeleton.
- Spines, about 30 per cluster, give shade.
| ~200 gal | soaked up in days after a big rain |
|---|---|
| 80 lb/ft | a water-filled trunk; adults weigh tons |
| ~80% | of its water can go before it dies |
| At night | it opens its pores (CAM) to save water |
| 4 in deep | shallow roots grab light rain fast |
| Below 15 °F | long hard freezes can kill it |
Roots: a 40 ft saguaro’s roots reach about 40 ft out but stay in the top 4 in (10 cm) of soil, plus a 2–5 ft taproot.
6.Blooms that open at night
The saguaro blossom is Arizona’s state wildflower. From late April to early June, creamy blossoms crown the stem and arm tips; peak bloom is mid-May to mid-June. Each flower lasts less than a day. Slide through a day and night.
Blossom openNight shift: lesser long-nosed bats drink the nectar and carry pollen.
12 am6 amnoon6 pm12 am
Times are approximate: a blossom opens around 10 pm and closes by about 3 pm the next afternoon.
- Pollinators: lesser long-nosed bats by night; bees and white-winged doves by day.
- Up to ~200 blossoms a plant in a season, clustered at the stem tips.
- The fruit ripens in June and July, about 3 in long, then splits open to show red pulp with 2,000 or more tiny seeds.
- The Tohono O’odham harvest the fruit with long poles made of saguaro ribs and boil it into syrup; the harvest starts their new year.
7.A saguaro’s year
Choose a month on the ring to see what the plant and the weather are doing.
Figure 9. The saguaro’s year as a ring, January at the top.
May
- Flowers · late Apr–early Jun
- Driest and hottest · May–Jun
Peak bloom begins in mid-May while the desert is at its driest. Bats work the flowers by night.
FlowersFruit ripensDriest and hottestMonsoon rainsSeeds sproutWinter rainsFrost risk
8.A desert apartment block
Birds, bats and mammals live on, in and around a saguaro, from the woodpeckers that dig the holes to the owls that move in later.
1
Gila woodpeckers and gilded flickerspeck out new nest holes every year. The plant seals each one with hard scar tissue.
2
Elf owls, purple martins, finches and flycatchersmove into the old holes. The sparrow-sized elf owl is a classic tenant.
3
Red-tailed and Harris’s hawks, ravensbuild stick nests in the crook of the arms.
4
Bats, doves and beessip the nectar and spread the pollen.
5
Javelina, coyotes and tortoisesfeast on the fallen fruit.
The saguaro boot
The hard scar tissue lining an old nest hole. It outlasts the cactus and is often found on the ground after a saguaro dies.
9.Saguaros and their look-alikes
Five other tall cacti, and one strange saguaro, get mistaken for the real thing. The models below are not to scale.
Organ pipe
Many stems rise from the base
Organ Pipe NM (Arizona), Sonora and Baja
10–20 ft
Senita
5–8 deep ribs; grey, shaggy “beard” on top
Southern edge of Organ Pipe NM, Sonora and Baja
to about 20 ft
Cardón
Huge, bulky trunk; arms branch low
Baja California and coastal Sonora
to ~60 ft; very bulky
Mexican fence post
Straight posts; 5–7 ribs lined in white
Central Mexico; a garden plant in Arizona
to about 15 ft
Crested saguaro
A rare fan-shaped crest at the tip
About 75 of the 1.9 million saguaros in Saguaro NP
cause still unknown
Crested saguaros
Now and then the growing tip of a saguaro fans out into a wavy crest instead of a rounded dome. Only about 75 of the 1.9 million saguaros in Saguaro National Park are crested, and the cause is still unknown.
A crest can form on the main stem or on an arm. It is still a saguaro: count its age the same way, by the height of the main stem.
ID helper
Is there a fan-shaped crest at the tip?
Name that cactus0 of 0
Clue: Organ Pipe NM (Arizona), Sonora and Baja.
10.Only in the Sonoran Desert
Wild saguaros grow in one desert only, between the frost to the north and east and the dry lowlands to the west.
Phoenix
Tucson
Hermosillo
Organ Pipe NM
- Southern Arizona and Sonora, Mexico, plus a few in south-eastern California along the Colorado River.
- Sea level to about 4,000 ft, higher only on warm, south-facing slopes.
- Frost sets the limits: too cold to the north, east and up high; too dry to the west.
- Protected by Arizona law; Saguaro National Park alone shelters about 1.9 million.
- Not in Texas. Despite old Western movies, wild saguaros grow only here.
11.Planting and care
Moving or planting a saguaro is mostly about patience. These steps follow University of Arizona Cooperative Extension advice (AZ1932).
- Keep the same compass sideMark the north side before digging. A plant turned round can sunburn.
- Plant no deeper than beforeRefill with dry native soil, no compost, and tamp it firm.
- Wait to waterHold off 2–4 weeks after planting, a month or more in cool weather.
- Then soak and let dryAbout every 3 weeks in summer, roughly 1 gallon per foot of cactus.
- Shade, brace, be patient30% shade cloth the first summer; keep watering for 4 years or more.
- Frost nightsCap young tips with a foam cup or frost cloth, never plastic.
- Trouble signsBlack ooze, soft or sunken spots or a new lean: call an expert.
Summer soak calculator
About 6 gallons
every 3 weeks or so in summer, once the first 2–4 dry weeks after planting are over. Let the soil dry between soakings; water less in cool weather.
Under 2 ft: a young saguaro this size nearly always survives a move. Larger plants are much harder to transplant.
12.Law and threats
Saguaros are protected by Arizona law, and the main threats are fire, freezes, drought and land clearing.
Arizona native plant law
- Permit and tag: removing a saguaro needs a permit and tag from the Arizona Department of Agriculture.
- Public land: digging up any saguaro needs a permit.
- Clearing land: owners notify the Department 20–60 days ahead.
- Penalties: violations are crimes, and costly thefts are felonies.
General information, not legal advice. Check current state and city rules (Arizona Revised Statutes, Title 3, ch. 7) before moving a plant.
Threats
- Buffelgrass: an invasive grass that fuels fires saguaros can’t survive.
- Hard freezes: long freezes kill; frost sets the northern limit.
- Heat and drought: hotter, longer dry spells kill young plants.
- Development: land clearing, plus theft of wild plants.
Sources and notes
All figures are approximate. Growth varies with rainfall, soil, frost and site; ages are estimates, heights beyond 150 years are rough extrapolations, and legal notes are general information, not legal advice.
- Average heights by age: Hodge (1991), via the Arizona-Sonora Desert Museum.
- National Park Service: Saguaro National Park and Organ Pipe Cactus National Monument.
- Arizona-Sonora Desert Museum.
- University of Arizona Cooperative Extension, AZ1932: transplanting saguaros.
- Arizona Revised Statutes, Title 3, ch. 7 (Arizona native plant law).
- Friends of Saguaro National Park.