SPINACH PRODUCTION IN
CALIFORNIA
STEVEN T. KOIKE, UCCE Farm Advisor, Monterey County;
MICHAEL CAHN, UCCE Farm Advisor, Monterey County; MARITA
CANTWELL, UCCE Vegetable Specialist, University of California,
Davis; STEVE FENNIMORE, UCCE Weed Specialist, U.S. Agricultural
Research Station, Salinas; MICHELLE LESTRANGE, UCCE Farm
Advisor, Tulare County; ERIC NATWICK, UCCE Farm Advisor, Imperial
County; RICHARD F. SMITH, UCCE Farm Advisor, Monterey County;
ETAFERAHU TAKELE, UCCE Area Advisor Agricultural Economic/Farm
Management, Riverside County
PRODUCTION AREAS AND SEASONS
California produces spinach (Spinacia oleracea) in
four areas: the southern desert valleys (Imperial and
Riverside Counties); the southern coast (Santa Barbara
and Ventura Counties); the central coast (Monterey,
San Benito, Santa Clara, and Santa Cruz Counties); and
the central San Joaquin Valley (Stanislaus and Tulare
Counties). Almost half of California’s spinach acreage
and production is in Monterey County. The southern
coast and San Joaquin Valley each produces about one-
fourth of California’s spinach, followed by Coachella
Valley in Riverside County.
Spinach is produced virtually all year in the coastal
valleys, with a slight dip in December and January in
both planting and harvest. In Coachella Valley planting
occurs from October through December for harvest from
November through March. In the San Joaquin Valley
planting starts in late October and continues through
January for harvest from February through April.
Spinach is marketed as three different commodities:
fresh market clipped and bagged, fresh market
bunched, and frozen. Fresh market clipped and bagged
is the dominant spinach product produced in California.
This bagged product is produced and sold containing
either very small, young leaves (“baby spinach”) or
slightly older, medium-sized leaves (“teenage spinach”).
Both baby and teenage spinach leaf sizes are usually
significantly smaller than the leaf size of the traditional
fresh market bunched spinach; freezer spinach leaf size
is the largest of all marketed sizes.
CLIMATIC REQUIREMENTS
Spinach is a quick-maturing, cool-season vegetable
crop. Seed germinate at 35º to 85ºF (2º to 30ºC), but
45º to 75ºF (7º to 24ºC) is optimal. Spinach will grow
from 40º to 85ºF (5º to 30ºC), but growth is most rapid
at 60º to 65ºF (15º to 18ºC). Spinach can withstand low
temperatures of 15º to 20ºF (–9º to –6ºC) without great
injury. Freezing weather harms small seedlings and
young plants, though more mature plants can tolerate
subfreezing temperatures for weeks.
Spinach produces a rosette of leaves that may be
wrinkled (savoy or semisavoy types) or smooth (flat
leaf types). Leaves are typically oval, rounded, or
triangular and are borne on a short stem. If the crop
is allowed to become overmature, the stem elongates
and produces a seedstalk with narrow, pointed leaves.
This seedstalk formation (bolting) is caused by late-
season high temperatures and long days, and crops
that are bolting are rarely marketable.
CULTIVARS
In California, the smooth or flat leaf spinach cultivars
are grown almost exclusively, though some semisavoy
types are used. All spinach cultivars commercially
grown in California are hybrids, primarily because
disease and bolting resistance have been bred into
these hybrids. Downy mildew is an economically
important foliar disease of spinach for which single-
gene resistance is incorporated as new races of the
Vegetable
Production Series
vric.ucdavis.edu
UC Vegetable Research
& Information Center
University of California
Agriculture and Natural Resources
http://anrcatalog.ucdavis.edu • Publication 7212
SPINACH ACREAGE AND VALUE
(FRESH MARKET)
Year Acreage
Average yield
(ton/acre)
Gross value
per acre
2008 25,500 8.25 $5,500
2007 23,500 8.75 $5,480
2006 30,000 9.0 $4,620
2005 32,500 9.0 $3,726
Source: California Agricultural Resource Directory
2006 (Sacramento: California Department of Food and
Agriculture, 2008).
http://vric.ucdavis.edu
http://anrcatalog.ucdavis.edu
pathogen develop. To keep bolting at a minimum,
physiological factors such as increased day length,
high temperatures, and inadequate fertility and
irrigation must be avoided or minimized. Processors
sometimes breed their own cultivars for their
contracted growers who are growing spinach for
freezing. However, in many cases fresh market
cultivars are also grown for the frozen commodity.
Some popular cultivars in California include the
following; numbers in parentheses after the cultivar
name indicate the downy mildew races (DM) to
which the cultivar is resistant: Avenger (DM 1–7, 9),
Bolero (DM 1–4, 9), Bossanova (DM 1–4, 9), Dolphin
(DM 1–7, 9), Emilia (DM 1–10), Falcon (DM 1–7),
Lazio (DM 1–10), Palco (DM 1–7), Unipak 144 (DM
1–5), and Whale (DM 1–7). However, cultivars are
always being developed, and newer ones are already
on the market.
PLANTING
All spinach is direct seeded. The California industry
is known for using very high seed planting densities
and a large number of seed lines per bed. In general,
baby and teenage clipped spinach is planted only
on 80-inch-wide (203-cm) beds, while bunched and
freezer spinach is grown on both 40-inch (100-cm)
and 80-inch beds. Spinach seed is planted 1⁄2 to 3⁄4
inch (1.2 to 1.9 cm) deep, depending on the method
of planting and soil conditions. The following table
summarizes general planting formats and days to
harvest. Note that the days to harvest information
pertains to coastal spinach production areas and
ranges from very short growing periods in late spring
through summer to longer growing periods in fall,
winter, and early spring. Versatility is also practiced,
for in some cases a fresh market spinach planting is
first clipped for fresh market product, then allowed
to regrow to a larger size for a second harvest for the
freezer.
SOILS
A variety of soils are used for spinach production,
but in most regions sandy loam soils are preferred. In
the inland valleys, soils with considerable sand are
desirable for winter and early-spring crops because
they are warmer and drain more efficiently. Harvesting
is often possible during rainy periods on sandy ground
when it is impossible to work on loamy clay soils.
Heavier soils can be quite productive if they are well
drained and irrigated with care. Spinach is particularly
sensitive to saturated soil conditions. Spinach is
moderately salt sensitive. Research has shown that
the soil salinity threshold for yield loss is from 2 to
4 dS/m at 25ºC (77ºF), depending on the frequency
of irrigation, soil type, and weather conditions. Yield
loss is about 8 percent for each additional increase of 1
dS/m of soil salinity.
IRRIGATION
Depending on the initial soil conditions, 2 to 4 inches
(5 to 10 cm) of water are applied using sprinklers to
moisten soil for tillage and seedbed preparation. All
spinach fields in California are sprinkler irrigated
to germinate the seed. Two to three irrigations are
required between seeding and emergence. During
the spring and summer months, short sprinkler
applications usually follow an initially long irrigation
every 2 days until emergence to prevent the formation
of a soil crust and to replace moisture lost by
evaporation. Most growers produce the entire crop
with sprinklers, though continued use of overhead
water favors infection and spread of leaf spot diseases.
Some processed crops grown in the central valley are
furrow irrigated. For short-cycle crops, such as baby
and teen spinach, solid-set sprinklers are often used
to minimize labor during the crop cycle. Operating
sprinklers in windy conditions can greatly reduce
irrigation uniformity and cause uneven emergence and
growth.
2 • Broccolli Production in California
SPINACH SEEDING RATES AND DAYS TO HARVEST
Spinach
commodity
40-inch beds
(million seed/ac)
40-inch beds
(seed lines/bed)
80-inch beds
(million seed/ac)
80-inch beds
(seed lines/bed)
Days to
harvest
baby leaf,
clipped
NA NA 3.5–4.0 24–48 21–40
teenage,
clipped
NA NA 2.7–3.5 21–48 26–50
bunched 1.2 6–9 1.5–2.3 12–21 32–62
freezer 0.8 6–9 1.0–1.5 12–21 48–90
Spinach has a relatively shallow root system and
thrives on frequent, short irrigations to maintain a
uniformly moist soil for maximum leaf production.
However, care must be taken to avoid saturated
conditions, as spinach is sensitive to overwatering,
especially on heavy soil textures. Saturated conditions
can contribute to soilborne diseases as well as to
abiotic rotting of the roots, crown, and lower leaves.
One to three irrigations are usually required between
emergence and harvest for clipped crops. The total
water applied between seeding and harvest is 4 to 8
acre-inches per acre (413 to 826 cu. m) for a clipped
crop, and 6 to 12 acre-inches per acre (620 to 1,240 cu.
m) for a fresh market bunch crop. Processed crops
may require 18 to 24 acre-inches per acre (1,860 to
2,480 cu. m), depending on the irrigation method and
weather conditions.
The combination of soil moisture monitoring and
weather-based irrigation scheduling can be used to
determine water needs of spinach. Water use is highest
when the leaf canopy is near maximum size. Soil
moisture tensions are typically targeted for less than 20
to 30 cbars (20 to 30 kPa). Water extraction of spinach
can be estimated using reference evapotranspiration
data, adjusted with a crop coefficient, that are closely
related to the percentage of ground covered by the
leaf canopy. Because evaporation represents a majority
of the water loss during the early stages of growth, a
crop coefficient between 0.3 and 0.5 should be used
for overhead sprinklers until the canopy is greater
than 30 percent cover. At a maximum canopy cover of
85 to 90 percent, the crop coefficient is nearly 1.0. The
California Irrigation Management Information System
(CIMIS), coordinated by the California Department of
Water Resources, provides daily estimates of reference
evapotranspiration for most production regions of
California (see http://wwwcimis.water.ca.gov).
FERTILIZATION
Fresh market spinach is a short-season crop that
is harvested when the crop is young. As a result,
nutrient uptake is relatively low. For instance, the
nitrogen (N) content of fresh market spinach may
vary from 20 to 40 pounds of nitrogen per acre (22
to 45 kg/ha). Freezer spinach is harvested at a more
mature stage, and the nutrient content may be double
that of fresh market spinach. Spinach is moderately
fertilized; the fertilizer rate should be determined
after consideration of type of spinach being grown,
soil type, recent cropping history, and soil test results.
Phosphorus (P) fertilization should be applied
based on soil test results for bicarbonate extractable
phosphorus. Levels above 60 parts per million (ppm)
are adequate for spinach growth; for soils below this
level, especially in the winter, preplant applications
of 20 to 40 pounds per acre of P2O5 (22 to 45 kg/
ha) or applications of 20 pounds per acre of P2O5
(22 kg/ha) at planting are recommended. The need
for potassium (K) can also be determined from soil
tests; soils with greater than 120 ppm of ammonium-
acetate-exchangeable potassium have sufficient
quantities for the crop. Potassium fertilization
presents no environmental risk, and many growers
routinely apply potassium even in fields with high
levels of exchangeable soil potassium. Fertilizing to
replace potassium removed with the harvested crop
(approximately 25 to 55 lb/acre, or 63 to 138 kg/ha) is
appropriate to maintain soil fertility for fresh market
spinach, but fertilization rates above that level are
economically wasteful.
Fall application of nitrogen is not recommended
due to the risk of NO3–N leaching beyond the root
zone by the winter rains. Small quantities of nitrogen,
20 pounds per acre (22 kg/ha), are applied preplant
or at planting; an additional topdress or water-run
application of 20 to 30 pounds of nitrogen per acre
(22 to 34 kg/ha) is generally sufficient for fresh
market spinach production. For freezer spinach, two
sidedress applications of nitrogen several weeks
apart may be necessary. Spinach plantings that follow
crops containing substantial nitrogen, such as lettuce
and cole crops, may benefit from useable residual
amounts of nitrogen. This nitrogen can be measured
with pre-sidedress soil nitrate testing (PSNT). Soil
nitrate levels greater than 20 ppm in the top 6 inches
(15 cm) are adequate for crop growth.
INTEGRATED PEST MANAGEMENT
Cultural control methods such as careful site selection,
mechanical cultivation, field sanitation, irrigation
management to avoid excessively wet soils, and crop
rotation are important components of an integrated
pest management (IPM) program that can help
minimize the use of chemical controls. Herbicides,
insecticides, and fungicides should always be used in
compliance with label instructions. Contact the UC
Davis IPM World Wide Web site at http://www.ipm.
ucdavis.edu or your local UCCE Farm Advisor for
current pest management information (see the UC IPM
Pest Management Guidelines for Spinach Web site,
http://www.ipm.ucdavis.edu/PMG/selectnewpest.
spinach.html).
Weed management. Weed management is
essential in spinach production given the use of high-
density plantings on 80-inch beds that preclude
the use of cultivation. There is also a low tolerance
for weeds in the mechanically harvested product.
Weed management depends on good preplant weed
control practices such as killing weeds prior to seed
set and carrying weeds from the fields; such practices
contribute to lowering weed populations in the soil
seedbank. Pregermination of weed seeds followed
3 • Spinach Production in California
http://wwwcimis.water.ca.gov
http://www.ipm.ucdavis.edu
http://www.ipm.ucdavis.edu/PMG/selectnewpest.spinach.html
by weed removal with herbicide, propane flaming,
or shallow tillage prior to planting can further reduce
weed pressure in both organic and conventionally
produced spinach. Hand weeding is generally
necessary for spinach production, but it can be made
more efficient and economical by effective weed
control practices described above. Stinging nettle
(Urtica urens) is one of the most troublesome weeds in
spinach. Other cool-season weeds that predominate
in spinach fields include annual bluegrass (Poa
annua), sowthistle (Sonchus oleraceus), prickly lettuce
(Lactuca serriola), little mallow (Malva parviflora),
mustards such as London rocket (Sisymbrium irio),
and shepherd’s purse (Capsella bursa-pastoris).
Chemical control of weeds includes the use of
herbicides and preplant fumigation with metam
sodium or metam potassium. Both metam products
are injected 3 inches (7.6 cm) deep into the soil and
sealed with sprinkler irrigation. Preemergence
herbicide is applied to control a spectrum of broadleaf
and grass weeds in fresh market spinach, and
postemergence herbicides are available to control
weeds in freezer spinach. Consult your local UCCE
Farm Advisor for advice on specific weed problems.
Insect and mite management. Because a significant
percentage of spinach is grown for use in prewashed,
packaged salad mixes, tolerance for insect damage
and presence of insects is extremely low. Hence, insect
management is critical for this commodity. Leafminers
are a serious problem in the production of spinach
in the coastal regions. Three species predominate
as pests: serpentine leafminer (Liriomyza trifolii),
vegetable leafminer (L. sativae), and pea leafminer
(L. huidobrensis). Damage by leafminers results
when female flies puncture leaves to feed on plant
sap and lay eggs in the leaf tissue. Adult “stings”
appear as holes or bumps on the spinach leaves. Adult
leafminers have such a preference for cotyledons that
seedling growth may be stunted. After eggs hatch,
larvae feed between the upper and lower leaf surfaces
and make distinctive winding, whitish tunnels or
mines. Mining reduces photosynthetic capacity of the
leaves and also renders them unmarketable.
Natural enemies, especially parasitic wasps in the
genus Diglyphus, can reduce leafminer populations
quite effectively; however, when insecticides
are applied for the leafminer adult or other pests,
parasites may be killed. Leafminer control with
insecticides targets either the adult fly by using
contact materials or the larvae with systemic
products. The use of insecticides for larval control is
longer lasting and less likely to result in reinfestation.
Cultural practices such as postharvest disking can
reduce migration of adult flies into nearby fields.
Several species of aphids are found on spinach in
California, but the green peach aphid (Myzus persicae)
is probably the most common. These pests stunt
plants, reduce yields through plant sap removal,
transmit viruses (especially Cucumber mosaic virus),
and result in contaminated spinach leaves due to
aphid honeydew, sooty mold, and debris. At certain
times of the year parasitic wasps and predators
provide natural control of aphids, while at other
times aphid populations increase rapidly and contact
or systemic insecticides may be needed.
Several worm pests attack spinach, but the most
common are loopers and beet armyworm. Several
insecticides are available for worm pest control,
but choose those least disruptive to parasites and
predators that suppress leafminers and aphid
populations. Rotate classes of insecticides for
resistance management.
Whiteflies and thrips are pests of spinach in
the southern deserts. In the southern deserts, the
silverleaf whitefly (Bemisia argentifolii, also known
as B. tabaci biotype B) stunts plants, reduces yields
through plant sap removal, transmits viruses,
and results in contaminated spinach leaves due
to honeydew, sooty mold, and debris. Several
insecticides are available for whitefly control and can
be applied to the soil at planting or as foliar sprays.
Rotating classes of insecticides is very important for
resistance management.
Spinach can sometimes be damaged by a bulb mite
called the spinach crown mite (Rhizoglyphus sp.). This
very tiny pest feeds on the very young leaves deep in
the plant crown; when these leaves expand, they are
distorted and torn. The mites are especially difficult
to see because of the naturally occurring glands
on developing leaves. Control must occur before
the damage is done, making careful monitoring for
this pest very important. Damage is usually most
severe in the early spring when plant growth is slow.
Spinach planted in fields with recently disked crop
residue or weeds is most susceptible.
Disease identification and management. An
integrated disease management approach, including
the use of disease-resistant cultivars, crop rotation,
careful irrigation, and fungicides, is necessary to
produce a high-quality product. As with insect pests,
the presence of disease symptoms is not tolerated for
the prewashed packaged salad products.
Damping-off disease caused by the complex
of Fusarium, Pythium, and Rhizoctonia fungi is
periodically a problem in spinach production.
Severity is influenced by cultivar, soil temperature,
soil moisture, and crop history. Severe damping-off
of spinach is associated with warm, wet soils with a
history of frequent spinach production. Management
practices typically include the use of a seed-treatment
fungicide and crop rotation with non-host crops.
Several diseases attack the leaves of spinach. Downy
4 • Spinach Production in California
mildew caused by Peronospora farinosa f. sp. spinaciae
is the most widespread and destructive disease of
spinach
