ASPARAGUS PRODUCTION IN
CALIFORNIA
BRENNA AEGERTER, UC Cooperative Extension Farm Advisor, San
Joaquin County; MICHAEL CAHN, UC Cooperative Extension Farm
Advisor, Monterey, Santa Cruz, and San Benito Counties; STEVEN KOIKE,
UC Cooperative Extension Farm Advisor, Monterey and Santa Cruz
Counties; RICHARD SMITH, UC Cooperative Extension Farm Advisor,
Monterey, Santa Cruz and San Benito Counties; TIMOTHY HARTZ,
Cooperative Extension Vegetable Crops Specialist, Department of Plant
Sciences, University of California, Davis; TREVOR SUSLOW, Cooperative
Extension Postharvest Specialist, Department of Plant Sciences, University of
California, Davis
PRODUCTION AREAS AND SEASONS
California has three primary asparagus (Asparagus
officinalis) production areas: the Sacramento–San
Joaquin River Delta (San Joaquin, Sacramento,
and Contra Costa Counties), the Central Coast
(Monterey and San Benito Counties), and the San
Joaquin Valley (Fresno, Kern, Merced, and Kings
Counties). However, asparagus is broadly
adaptable, and limited acreages of asparagus are
grown in various other parts of the state, from the
Sacramento Valley in the north to the Imperial Valley
in the south. Asparagus is a perennial crop that
is normally harvested once per year over an 8- to
12-week period. The main harvest season is in the
spring, but some may be cut in the fall (September
and October). Asparagus may be harvested from
January to early April in the southern desert valleys,
from late February through May in the Delta and the
San Joaquin Valley, and from March to mid-June on
the Central Coast. California produces only green
asparagus; white asparagus is no longer produced.
Most California-grown asparagus is sold for the fresh
market; less than 1% of the crop is processed. The
harvested acreage for 2009 was 12,500 acres, a decline
of 63% from the acreage harvested in 2004.
CLIMATIC REQUIREMENTS
Asparagus favors temperate climates. Optimal root
and fern (foliage) growth occurs from 65º to 85ºF (18º
to 29ºC). Spear (edible shoot) initiation occurs at soil
temperatures above 50ºF (10ºC); spear elongation
is faster at higher air temperatures. Root and fern
development are reduced at temperatures below
55ºF (13ºC) or above 85ºF (29ºC). High temperatures
cause the spear tips to open (“feather”) prematurely,
reducing overall spear quality.
VARIETIES AND PLANTING
TECHNIQUES
Varieties. The principal cultivars grown are UC157
and De Paoli, with limited acreages of other varieties.
Planting. Although asparagus can be established
by direct seeding or transplanting of greenhouse-
grown seedlings, current plantings are established
with field-grown 1-year-old crowns. October through
March is the best time for planting transplants or
crowns. Crowns are normally placed in the bottom of
a furrow and soil is mounded over the plants as they
develop to fill in and form a raised bed. Bed width
varies from 40 to 72 inches (100 to 180 cm), depending
on grower preference. In-row spacing for crowns
is usually 6 to 12 inches (15 to 30 cm). In the desert,
there are normally two rows per 60-inch (1.5-m) bed,
giving a population of 17,000 to 20,000 plants per acre
(42,500 to 50,000 plants/ha). Plant populations using
one row per bed vary from 9,000 to 13,000 plants per
acre (22,500 to 32,500 plants/ha).
SOILS
Careful attention should be given to field selection
because asparagus will occupy the land for 8 to
10 years. Fields should be uniform in soil type to
Vegetable
Production Series
vric.ucdavis.edu
UC Vegetable Research
& Information Center
University of California
Agriculture and Natural Resources
http://anrcatalog.ucdavis.edu • Publication 7234
ASPARAGUS ACREAGE AND VALUE
Year Acreage
Average yield
(ton/acre)
Gross
value/acre
2009 12,500 1.60 $4,160
2008 14,500 1.45 $3,625
2007 20,000 1.45 $3,509
2006 22,500 1.15 $2,714
Source: california Agricultural Statistics 2009 (Sacramento:
California Department of Food and Agriculture, 2010).
http://vric.ucdavis.edu
http://anrcatalog.ucdavis.edu
facilitate the timing of irrigation that is appropriate
for the whole field. Locations known to have
problems with bermudagrass (Cynodon dactylon),
field bindweed (Convolvulus arvensis), johnsongrass
(Sorghum halepense), or nutsedge (Cyperus spp.) are
poor choices for asparagus production because
these perennial weeds are difficult to control in
established asparagus. The ideal pH for asparagus
is 6.5 to 7.5. Acidic conditions (less than pH 6.5)
can lead to reduced growth and yield. Corrective
annual applications of lime may be necessary to
elevate pH levels. Asparagus has a high tolerance
for salt; a saturated soil extract can have an electrical
conductivity (EC) as high as 6 dS/m with no impact
on yield.
In the principal asparagus production area of
California, the Sacramento–San Joaquin River Delta,
most of the soils are high in organic matter and have a
high water table. Care must be exercised in applying
water to these soils to prevent the development of
soilborne diseases. Provisions are made for drains
and pumps to remove water that accumulates from
irrigation and rainfall. In areas adjacent to the San
Joaquin Delta and along the Central Coast a wide
variety of sedimentary soils (ranging from sandy
loam to some clay loams) are used for asparagus
production. Shallow soils or those with a perched
water table should be avoided, as these conditions
lead to a short stand life due to unhealthy or diseased
roots.
IRRIGATION
Water is required to replace moisture lost by
evapotranspiration and to leach salts that have
accumulated in the soil. The volume of applied
water varies greatly among production regions. In
the Imperial valley, 48 to 60 inches of water (14,640
to 18,300 mm) is applied; in the San Joaquin Valley
and Central Coast areas 18 to 30 inches (5, 490 to
9,150 mm) is applied to mature plantings. In the San
Joaquin Delta, a significant portion of the water needs
of asparagus are supplied from a shallow water table.
As new plantings emerge in the spring, frequent
irrigations may be needed to maximize fern growth.
As fern growth increases in established plantings
after harvest, applied water is increased to match
the water extraction of the crop. Water applications
are cut back in late summer and early fall to curtail
new fern growth as the crop transitions into winter
dormancy. Although asparagus is considered to be
drought tolerant, if water is cut back too severely,
spear yield and size can decline during the
subsequent harvest season. After removal of ferns in
the fall, crop water requirements are low. Formerly,
in the San Joaquin Delta, many of the fields high in
organic matter were flooded for a period of 30 days
during the winter, when the crop was dormant, to
refill the soil profile and leach accumulated salts.
Oversaturating the soil during cool conditions can
exacerbate root diseases. More commonly today, a
single heavy irrigation is done in late December or
early January. Other production fields on sedimentary
soils in the Delta and on the Central Coast rely on
winter rainfall or irrigation before harvest for early-
season moisture.
In the desert region, fields are usually irrigated
to moisten the soil before harvest and periodically
irrigated to maintain moisture near the soil surface
during harvest. Asparagus spear size and yields
are higher if soil moisture is maintained near field
capacity during the harvest period. Irrigations are
made to alternate furrows to maintain a dry furrow
for foot traffic during harvest. Because of the long
harvest period on the Central Coast, periodic
irrigations are also required to maintain moisture
near the soil surface. Overhead sprinklers are
also used during the harvest period because light
applications can be made to allow harvest crews and
equipment access into fields within a few days after
irrigating.
Asparagus is typically furrow irrigated in all
growing regions of California. The interval between
irrigations during the summer is from 10 to 15 days
(longer in the Delta, where some of the water may be
supplied from a shallow water table). Approximately
3 to 6 inches (915 to 1,800 mm) of water is
applied with each furrow irrigation. Overhead
sprinklers may also used to irrigate asparagus during
the summer.
The use of subsurface drip irrigation in asparagus
is increasing in California. Drip permits growers to
irrigate during the harvest period without impeding
field access by harvest crews and equipment. One
line of drip tape per bed is placed 3 to 6 inches (7 to
15 cm) below the depth of the crown. Tape with a
wall thickness greater than 10 mil is recommended to
resist puncture from soil insects. Irrigation needs for
drip irrigation can be determined by weather-based
reference evapotranspiration (ETo) estimates and crop
growth stage; frequency of irrigation can vary from
once per week early in the season to 2 to 3 times per
week during periods of peak water demand.
A combination of soil moisture monitoring
and weather-based irrigation scheduling can be
used to determine the water needs of asparagus.
Water use is highest when ferns reach maximum
size. Irrigations should be scheduled when soil
moisture tensions are above 50 centibars (50 kPa).
Water extraction of asparagus can be estimated
using reference evapotranspiration data adjusted
with a crop coefficient, which is closely related to
the percentage of ground covered by the canopy.
2 • Asparagus Production in California
At a maximum canopy cover of 85%, the crop
coefficient is nearly 1.0. The California Irrigation
Management Information System (CIMIS, www.
cimis.water.ca.gov) coordinated by the Department of
Water Resources provides daily estimates of reference
evapotranspiration for most production regions of
California.
FERTILIZATION
Fertilization practices for asparagus production
depend on the field conditions and the age of the
planting. In preparing a new field for planting the
soil test levels of phosphorus (P) and potassium (K)
should guide fertilization rates. Fields with Olsen
(bicarbonate-extractable) soil phosphorus greater
than 15 ppm have modest preplant phosphorus
requirements of less than 100 pounds per acre
(112 kg/ha) of P2O5, while fields with less than
10 ppm soil phosphorus may require 200 pounds
per acre (224 kg/ha) of P2O5 or more. Fields with
exchangeable soil potassium greater than 150 ppm
potassium require no preplant potassium, while
fields with less than 100 ppm may benefit from
application of up to 200 pounds per acre (224 kg/
ha) of K2O. Once an asparagus planting is established
and producing, the annual phosphorus and
potassium removal by the spears is modest; annual
maintenance applications in the range of 50 pounds
per acre (56 kg/ha) of P2O5 and 50 to 75 pounds per
acre (56 to 84 kg/ha) of K2O should be adequate to
maintain soil fertility. In the first 2 to 3 years after
establishment, annual nitrogen (N) rates of up to
200 pounds acre (224 kg/ha) may be used to build
up the nitrogen stored in the crowns. On established
plantings that are efficiently irrigated, annual rates
of 100 to 150 pounds per acre (112 to 168 kg/ha) of
nitrogen should be sufficient. Nitrogen application is
most efficient during active fern growth.
INTEGRATED PEST MANAGEMENT
Detailed information about IPM for asparagus is
available at the UC IPM World Wide Web site, http://
www.ipm.ucdavis.edu (see UC IPM Pest Management
Guidelines for Asparagus, ANR Communication Services
Publication 3435, 2009). Herbicides, insecticides,
fungicides, and preplant fumigants should always be
used in compliance with label instructions.
Weed management. Weeds can become a
serious and costly problem in both newly planted
and established asparagus. Selection of a relatively
weed-free planting site is essential. Prior to planting,
irrigation to germinate weeds followed by cultivation
or application of a postemergence herbicide, or
both, can aid in reducing weed competition. On
established asparagus, a preemergence herbicide
should be applied prior to the start of the harvest
season; some preemergence herbicides can be
applied during the cutting season. Water in the
form of rainfall or sprinkler irrigation is needed to
activate the herbicide. During the cutting season, spot
treatments with an herbicide may be necessary to
control weeds such as bermudagrass (Cynodon spp.).
A good time to control weeds mechanically, and to
apply preemergence herbicides for specific broadleaf
and grass weeds, is after the harvest season, before
the field is allowed to fern. Winter weed control can
be accomplished mechanically or with preemergence
herbicides.
Insect identification and control. Western
yellowstriped armyworm (Spodoptera praefica),
beet armyworm (Spodoptera exigua) , bean
thrips (Caliothrips faciatus), western flower thrips
(Frankliniella occidentalis), onion thrips (Thrips tabaci),
cutworms (Peridroma saucia and Euxoa messoria)
and asparagus beetle (Crioceris asparagi) have been
occasional pests requiring insecticide treatments.
When found in maturing ferns, the European
asparagus aphid (Brachycorynella asparagi) is the
most serious pest requiring insecticide treatments for
control. Asparagus miner (Ophiomyia simplex) may
need to be controlled periodically in the Imperial
Valley. Garden symphylan (Scutigerella immaculata),
a white arthropod closely related to insects, may
cause damage to asparagus roots and crowns, leading
to some crop stand loss if found in large numbers.
Garden symphylans typically are most severe in
soils with high levels of organic matter. A preplant
application of a fumigant or a soil-active insecticide
can control this pest. Effective controls for postplant
management have not been developed.
Disease identification and management. Fusarium
crown and root rot (Fusarium oxysporum, f. sp. asparagi,
Fusarium verticilliodes, and F. proliferatum) is the most
serious disease affecting asparagus production
worldwide. Fusarium causes a slow decay of the crown
and reduces spear size and number, ultimately leading
to lower yields. The problem increases with the age of
the crop stand. Severity of the disease can be reduced
by selecting vigorous-growing varieties (hybrids),
planting clean seed and one-year-old crowns grown
in noninfested soil, and practicing good irrigation
management. Replanting asparagus in the same
field should be avoided for at least a 10-year period.
Fusarium has a drastic effect on younger asparagus
plantings in infested soil. Excessive harvesting of
mature asparagus weakens the crowns and increases
stand decline caused by Fusarium crown and root rot.
Asparagus crown and spear rot (Phytophthora
megasperma var. sojae and other Phytophthora spp.) is
a soilborne fungal disease that is a particular problem
in soils that are saturated due to poor drainage, heavy
rainfall, or excessive irrigation. Crown and spear rot
and can occur if corrective and preventive measures
3 • Asparagus Production in California
http://www.cimis.water.ca.gov
http://www.cimis.water.ca.gov
http://www.ipm.ucdavis.edu
http://www.ipm.ucdavis.edu
are not employed, resulting in stand loss and reduced
production. Chemical and cultural controls can be
employed against this disease.
Asparagus rust (Puccinia asparagi), a fungal
disease affecting the asparagus fern, may require
chemical control during some years. Good irrigation
management, wide row spacings, orientation of
planted rows with the prevailing wind, and thorough
removal and destruction of infected fern may help
reduce the incidence or severity of asparagus rust.
Asparagus purple spot (Stemphylium vesicarium)
may occur during cool, wet weather at harvest. It
causes oval-shaped purple spots on the spears. The
spots elongate and produce grayish white, slightly
sunken centers within the lesion. The primary
source of inoculum for purple spot is fern debris
from the previous season’s crop. Good sanitation,
including fern chopping and soil incorporation of the
debris, minimizes occurrence of the disease under
California’s climatic conditions.
Asparagus viruses I and II (AVI and AVII) are
symptomless, latent diseases that can decrease
production and reduce plant vigor over time,
particularly when both viruses are present in a field.
AVI is insectborne and moves through a field as
insects move pollen from an infected male plant to
female plants. AVII is the more serious of the two
because it is seedborne and has been spread to some
degree into most asparagus production areas in
California. The best control measure is to plant fields
with certified virus-free seed or transplants cloned
from healthy mother plants. AVII is also spread by sap
on cutting knives during harvest. It has been shown
that AVII predisposes plants to further damage from
Fusarium crown and root rot.
HARVESTING AND HANDLING
Mature ferns are either chopped, often as part of the
green trash hauled from the field, or windrowed with a
swather. After drying, chopped ferns are incorporated
into the bed with a rotary power tiller. Fern chopping
occurs from late November to early December in the
desert and Delta growing areas. Following chopping,
the planted beds are reworked to loosen the surface soil,
reshaped, and fertilized.
Emerging spears are hand-cut. Early in the season,
fields are harvested every 2 or 3 days, but during
warm weather fields are cut daily. Spears are cut at
an angle just below the soil surface with an asparagus
knife. Spindly or otherwise deformed spears are cut
and discarded to allow for growth of marketable
spears. Cut spears must be approximately 10 inches
(25 cm) long to allow for a trim to 9 inches (22.5 cm)
during packing. Harvested spears are placed on the
beds in bunches, gathered, and placed in field boxes
or cart-carrying tractors. They are then taken out of
the field and hauled to sheds for grading, packing,
trimming, and cooling.
Defects and loss of production at harvest can
occur for various reasons. Drying wind and blowing
sand can dry out the cells on the side of the spear
facing the wind causing the spear growth to bend
into the wind. Spears can grow at a rate of 3 to 6
inches (7.5 to 15 cm) per day, depending on the
temperature (faster when warmer). Windborne soil
debris may also pit the emerging spears, making
them unmarketable. Trampling or inadvertent
cutting of emerging spears and high temperatures
cause misshapen spears. Cutting spears too far
below the ground may cause the additional loss
of spears that never reach the bed surface. High
temperatures can cause small-diameter spears,
tapered spears, loose heads, and premature breaking
of the bracts, especially in small spears. This
premature breaking is commonly referred to as
feathering. Harvesting a bed for too long during
the season may also cause spear feathering due to
low carbohydrate levels in the crowns. Thrips and
mite feeding can cause significant reduction in the
cosmetic appearance of spears.
Freezing temperatures during spear emergence
can cause frosting, a discoloration of green spears.
Frosted spears may still be marketable, albeit at a
reduced value, but most often they are discarded.
If spears are cut while frozen, damage is usually
severe and the product is not marketable. Ice
formation may be difficult to see because the ice is
clear, a condition known as black ice. A field with
black ice will be a darker green than normal.
Excess harvesting leads to a decline in production
and a proliferation of small spears. Fields in their
second year of production after transplanting
(crowns or seedlings) may be harvested, yielding 25
to 50 28-lb-cartons
