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Abstract
This publication discusses asparagus variety selection, insect
pests and diseases, weed control, harvest and post-harvest handling
for organic asparagus.
This publication
contains references to enclosures which are available in hard
copy only. Please call our toll free number to receive a copy.
1-800-346-9140 |
Table of Contents
Introduction
Asparagus has excellent potential as a fresh crop for local markets.
According to Pick-Your-Own Farming (1),
a practical handbook on truck farming and direct marketing by Wampler
and Motes, asparagus has been among the top ten moneymakers. Before
planting, though, farmers should make sure that the local market
for asparagus is not already saturated. To estimate how many acres
to plant, first determine the population residing within 25 miles
of the farm. One acre of asparagus for every ten thousand people
is a good rule of thumb.
Direct fresh-market options include pick-your-own, roadside stands,
farmers’ markets, and peddling to local grocery stores or
restaurants. Growers may also be able to market part of their asparagus
crop through brokers, wholesale chains, or processors if the local
market becomes saturated.
Organic crop production disallows the use of synthetic pesticides
or conventional commercial fertilizers. Instead, organic growers
rely on biodiversity, cultural practices, and alternative, environmentally
friendly inputs. As a commercial crop, asparagus can be somewhat
challenging to produce organically because of potential difficulties
managing weeds.
Because asparagus is a perennial crop that will be in the ground
for at least 10 to 15 years, attention to selection and preparation
of the planting site is especially important. Asparagus performs
best if the soil pH is within a range of 6.5 to 7.5. Phosphorous,
potassium, and lime amendments—based on a soil test—should
be incorporated prior to planting. If perennial weeds are a problem,
a sequence of tillage and cover cropping—with smother crops
like sorghum-sudan or buckwheat—at least a year in advance
of planting will help control weeds. Green manure crops also improve
soil structure and enhance soil fertility.
Variety Selection
Variety selection is a critical decision to be made prior to planting.
A number of highly productive asparagus varieties are available.
UC-157 and its hybrid lines replaced Mary Washington as the leading
commercial variety many years ago. Among the more recent developments
is the release of nine all-male hybrid varieties in the Jersey line
(e.g., Jersey Giant®, Jersey King®, etc.) Research has shown
these all-male hybrids to yield 2.5 to 3 times more than Mary Washington.
Also of possible interest for local specialty marketing is Purple
Passion, a burgundy-colored variety that is sweeter-tasting than
green types. The enclosed article by Carl Cantaluppi provides descriptions
of many common varieties. For further information on varieties and
which perform best in select regions, please contact Cooperative
Extension and local nurseries.
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Insect Pests
Several insect pests affect asparagus. The most damaging insects
include the asparagus beetle, spotted asparagus beetle, and asparagus
aphid.
The asparagus beetle is a common pest wherever asparagus is grown.
Both adults and larvae feed on the plant. In the spring they feed
on the spears and reduce the quality of the crop. In the summer
they defoliate the ferns and reduce the food supply to the crowns,
thus affecting future yields.
Spotted asparagus beetle is also widespread but is more common
in the Eastern United States. Adult spotted asparagus beetles emerge
later than common asparagus beetles. The injury caused by the adult
is similar to that of the common asparagus beetle; however, the
larval stage does little damage to the crop because it feeds primarily
on the fruits or berries.
Sanitation is one of the principal preventative strategies for
suppressing these pests. This usually involves fall/winter burning
of dried fronds and other “trash” to eliminate sites
where the beetles overwinter. (2) However, this
may be undesirable if it leaves the soil vulnerable to erosion.
On small acreages, enclosing the asparagus beds and letting hens
forage on the beetles is one possible strategy for control. (3)
Rotenone or rotenone-pyrethrum mixtures are an organic control measure
for larger acreages. Natural predators include a chalcid wasp and
lady beetle larvae.
Asparagus aphid is a European native that was first reported in
the U.S. in 1969. It has since spread across most of the country.
Asparagus aphid feeding causes bushy, stunted new growth called
“witches broom.” If not controlled by natural predators
and parasites, aphids are readily managed using insecticidal soap
and rotenone-pyrethrum sprays.
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Disease Pests
Asparagus is affected by an array of diseases, of which the following
are the most common and troublesome:
Fusarium, which causes assorted crown and root rots and
wilts, results in poor stands and yellowing and wilting of seedlings
in new plantings. In established plants, wilting of individual ferns
occurs and the foliage turns yellow to tan. Diseased crowns will
have a yellowish-red internal discoloration, and the major roots
will be rotted. The severity of fusarium wilt varies between different
asparagus growing regions in the country. In most instances, fusarium
rarely becomes serious in well-managed plantings. If fusarium does
become serious, the field may have to be destroyed and not replanted
to asparagus. (4) Salt has been found to be
somewhat effective in suppressing fusarium. See further discussion
on the use of salt in the section on weed control. Note that the
use of salt in this manner may not be acceptable for organic certification.
Asparagus rust (Puccinia asparagi) can be a problem if
the cultivars being grown are not rust-resistant. Rust can cause
premature defoliation or death of the ferns, reducing yields and
increasing the incidence of root or crown diseases. (5)
Symptoms generally occur after the cutting season. Small yellow-to-orange
spots first appear on the “needles;” in the second stage
of the disease, dusty brick-red pustules appear on both the shoots
and the needles; later they turn black. Rust is most severe during
times of heavy rain, high humidity, or abundant dew. Planting resistant
cultivars is the best control. Increasing the planting distance
between rows and orienting the rows toward the prevailing summer
winds will also help. Needle blight (Cercospora asparagi)
has recently become a problem disease of asparagus, especially on
the newer hybrid cultivars. Like rust, needle blight is a defoliating
disease prevalent during periods of high humidity or abundant rain
and warm temperatures. A bad infection will severely reduce yield
the following season because defoliated ferns do not manufacture
and store carbohydrate food reserves very well. Symptoms appear
in June, when affected ferns develop buff to gray, somewhat elliptical
spots surrounded by a thin purple band. (5)
The lush fern growth typical of the new hybrids, especially when
grown in rich organic soils, reduces air movement and creates ideal
conditions for the disease.
Tillage can reduce needle blight. However, Oklahoma researchers
found that burning the fern residue provided significantly greater
control than tillage and is recommended as the best cultural option.
(6) As with rust, increasing the planting distance
between rows (e.g., from 5 ft. to 6 ft.) will improve air flow and
help prevent disease buildup.
Purple spot, a fungal disease that infects young spears of asparagus,
is caused by Stemphylium vesicarum. Infection causes sunken
purple spots that reduce the value of the crop. Burying asparagus
debris in late fall or late winter significantly reduces the severity
of the disease. (7) Burying also reduces the
level of infection on young volunteer asparagus—an important
control measure because infected volunteers are the source of fungal
inoculum during the harvest period.
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Weed Control
Weed control is the most serious challenge facing organic asparagus
producers. Since asparagus is a perennial crop that increases in
bed-width each year, cultivation for weeds “in the row”
during spear harvest, and following harvest during fern production,
is not possible. Thus, elimination of perennial weeds such as bermudagrass,
quackgrass, johnsongrass, and nutgrass prior to planting is especially
critical. Annual weeds can be controlled through a combination of
cultural, mechanical, and biological control techniques.
Cultivation
To control winter annual weeds that have emerged in the field,
cultivate at a shallow depth after the winter ferns (i.e., trash
ferns from previous season) have been mowed or burned off. Avoid
damage to crowns by straddling the beds. At no time should tractor
tires be driven on or across the rows. Following harvest the field
should be disked or tilled again to eliminate weeds that have emerged
since the last cultivation and to prepare the field for summer fern
production.
Cultivation between the rows with a high-clearance tractor and
3-point hitch-mounted row cultivators will control the bulk of interrow
weeds during the growing season. During harvest of spears and during
fern production, in-row cultivation opportunities are limited. Yet,
these in-row weeds pose the greatest threat because weed competition
with ferns interferes with crown storage and reduces yield the following
growing season.
Mulches and weeder geese
During fern production, alternative weed control options in the
row include hand weeding, mulching, and/or the use of weeder geese.
On large-scale operations, mulching can be mechanized using straw
spreaders or forage wagons carrying green chop or shredded dry mulch.
Weeder geese are an alternative to mulching, and have a history
of use in asparagus. Contact ATTRA for additional information on
weeder geese.
Flame weeding
Flame weeding, which is done with propane flamers, is another possibility
for in-row weed control. Hand-held or backpack flamers can be especially
useful for spot treatment, though tractor-drawn rigs are available.
As a general rule, flame weeding is most effective against annual
broadleaf weeds, moderately effective against annual grasses, and
a poor option for perennial weed management. Flaming should be considered
a potentially useful though experimental tool. ATTRA has additional
information on the uses of flame weeding in vegetables, available
on request.
Cover crops
Cover crops are another useful tool in asparagus weed management.
Two cover crop systems that have potential in asparagus are “dying
mulches” and “living mulches.”
Dying Mulches
A dying mulch is a cover crop planted out of season. While growing
it suppresses weeds; then it dies back out on its own without requiring
the use of herbicides, mowing, or tillage. Winter rye—planted
in the spring—has been used successfully in this manner in
several agronomic and horticultural crops.
In asparagus here’s how this might work. Following post-harvest
tillage of the asparagus field, the field is over-seeded with winter
rye at 120 lbs. per acre to establish the living mulch. Since the
winter rye is planted in late spring, and consequently does not
receive normal winter vernalization (cold treatment), it never tillers
(i.e., it stays short) and eventually “cooks out” by
mid-summer. By this time, the asparagus ferns form a thick canopy
that shades out most underlying weeds.
The success of this system is dependent on proper timing and good
luck. Timing is critical to get the rye established early enough
to promote germination when the soil temperatures are still relatively
cool, but at the same time, late enough that a cold spell is avoided.
Vernalization can occur when the rye is exposed to only 10 days
of 45° F night temperatures.
Dr. Astrid Newenhouse, formerly with the University of Wisconsin,
conducted cover crop research in horticultural crops and provided
some preliminary insights into dying mulch and living mulch systems
for asparagus. Dr. Newenhouse tried the non-vernalized rye system
described above. She agreed that timing was critical with respect
to a cool spell. As a result of a cold snap one year, her rye headed
out and created additional management problems. Biological farming
strategies, like conventional farming strategies, don’t always
work as expected. (8)
Living Mulches
Living mulches are cover crops grown in association with annual
or perennial crops, primarily for weed suppression and as a soil
management practice. The goal is to plant a low-growing cover that
suppresses weeds without competing too much with the main crop.
In Wisconsin, Dr. Newenhouse’s living-mulch work in asparagus
focused on two cover crops: perennial ryegrass and ‘Dwarf
White’ Dutch white clover. Both cover crops were fall-established
and managed the following growing season with one to three mowings
using a walk-behind sickle-bar mower. Preliminary results indicated
that perennial ryegrass performed better than the Dutch white clover
the first growing season. However, in the second growing season
these results were reversed, with the Dutch white clover performing
better. This research found that living mulches could be highly
effective in weed suppression but also quite competitive with the
crop, reducing asparagus growth 50-75% in some instances. (9)
Clearly, more research is required to find living mulch systems
that are more viable.
The ATTRA publication Pursuing
Conservation Tillage for Organic Crop Production has additional
information on the use of cover crops for vegetables.
Salt
For generations, grower recommendations have included the application
of salt to the soil because plantings were observed to respond favorably
and weeds were suppressed. The practice fell into disfavor with
the introduction of herbicides. It did not revive in the organic
community, ostensibly because salt can be detrimental to soil structure.
More recently, however, researchers have learned that salt helps
control fusarium crown and root rot. It is this factor that is believed
to be of the greatest benefit to asparagus. (10)
As a weed control agent, salt is only reasonably effective against
young, germinating seeds; it does not kill established weeds nor
does it provide a long-lasting effect. Sodium chloride (basic rock,
table, or pickling salt) may be used. Applications of 1 lb. per
20 row feet (spread to a width of 2.5 feet) are recommended. (11)
Reasonable caution should be used; while asparagus is salt tolerant,
excessive levels can damage the crop and the soil. As mentioned
earlier, this tactic may not be permitted in certified organic production.
Growers should consult their certification agent before using salt
in this manner.
Herbicides
Herbicides, though prohibited in certified organic production,
are commonly used in integrated pest management programs. The number
of herbicide combinations available now also make it possible to
manage weeds in the row at reduced-input rates and still manage
between-row weeds through cultivation or use of living mulches.
Herbicide recommendations are available through the Extension Service.
Corn gluten meal is accepted in organic production and has proved
effective as a pre-emergent herbicidal material. It would likely
be effective in controlling some weeds in asparagus and could become
an option for organic producers. However, at recommended application
rates the cost would be quite high at present.
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Asparagus Harvest
The harvest period in a mature asparagus planting lasts about eight
to nine weeks. Spears are hand picked by snapping them just above
the ground. Most growers build their own harvest aids to increase
harvest efficiency. These low-lying platforms can either be attached
to the front or rear end of a tractor, or be self-propelled.
The Oklahoma State University Vegetable Research Station (12)
in Bixby, Oklahoma, built a self-propelled harvest aid that seats
three workers. The person in the middle steers with their feet while
picking. During full harvest it usually takes about 45 minutes to
pick an acre using this 3-seater, according to OSU Extension Vegetable
Specialist Jim Motes. (13) Motes said that
it takes about two person-hours per acre to harvest asparagus, regardless
of whether it is picked by stoop labor or with a harvest aid. The
main advantage of a harvest aid is the ability to work longer hours
without back strain.
Self-propelled harvest aids are also produced commercially. Holland
Transplanter Company (14) manufactures units
(similar to the one used in Oklahoma) that seat from one to six
workers and range in price from $6,000–$8,000. A single-seat
pedal-powered Crop Cart is available from Rusty’s Ag Sales.
(15) It sells for $975 and can be shipped by
UPS. Various articles describing other harvesting carts are included
among the enclosures.
Well-drained soils, such as a light, sandy loam, are a definite
advantage in asparagus production, especially when it comes to harvesting.
The ability to drive equipment into the field soon after it rains
is especially important. Once harvest begins, picking takes place
every other day in cool weather, and every day later in the season.
When harvest is delayed by wet field conditions, the spears may
open up and begin to fern out. As loose spears are non-marketable,
it is sometimes necessary to clear the whole field. This can be
accomplished by using either a sickle-bar mower or brush-hog. Again,
care should be taken to keep tractor tires off the rows to avoid
crown damage. Spear emergence following “clear-cutting”
gets the harvest back on schedule but overall yields and the harvest
season may be reduced.
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Post-harvest Handling
As asparagus is a highly perishable crop, some method of cooling
after harvest is necessary. Precooling to remove field heat prior
to shipment is commonly practiced via hydrocooling. Hydrocooling
is accomplished by flooding, spraying, or immersing vegetables in
chilled water. Following hydrocooling, asparagus should be kept
refrigerated.
According to the USDA:
Fresh asparagus is highly perishable and deteriorates rapidly above
41° F. Thus, the spears should be cooled immediately after cutting,
preferably by hydrocooling, and placed at a low temperature. In
addition to general deterioration, growth, loss of tenderness, loss
of flavor, loss of vitamin C, and development of decay take place
at moderately high temperatures.
Asparagus can be kept successfully for about 3 weeks at 35°
F. It can be held for about 10 days at 32° F., but is subject
to chilling injury when held longer at this temperature. (16)
High relative humidity (95 to 100 percent) should be maintained,
with good ventilation to reduce carbon dioxide and ethylene buildup.
Non-perforated film should not be used. Commonly, the desired relative
humidity is obtained by placing the butts of asparagus on wet pads.
Enclosed for your information is Post-harvest Handling of Fresh
Market Asparagus: A Brief Review, a University of California
Extension information sheet. It provides a useful guide to maintaining
quality from the field to the supermarket.
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White Asparagus
White asparagus is produced when spears are grown in the absence
of light. White asparagus has a milder flavor than green asparagus
and thus brings a higher (“gourmet”) market price. The
traditional practice for blanching asparagus was to mound up soil
or straw over the asparagus row. Hand labor was required to manage
and harvest the mounds and consequently the mound technique is no
longer practiced in the U.S.
Dr. Don Makus, while research horticulturist with the USDA Agricultural
Research Service in Booneville, Arkansas, perfected the use of simple
row tunnels covered with black, opaque plastic to produce white
asparagus. (Dr. Makus has since relocated to a USDA station in Texas.)
Enclosed is White Asparagus Production Using Opaque Plastic
Covers, an article describing this technique.
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References
- Wampler, Ralph L. and James E.
Motes. 1985. Pick-Your-Own Farming. University of Oklahoma Press,
Norman, OK. 194 p.
- Ellis, Barbara and Fern Marshall
Bradley. 1992. The Organic Gardener’s Handbook of Natural
Insect and Disease Control. Rodale Press, Emmaus, PA. p. 271.
- Philbrick, Helen, and John Philbrick.
1974. The Bug Book, Harmless Insect Controls. Storey Communications,
Inc., Garden Way Publishing, Pownal, VT. 124 p.
- Barnes, George L., et. al. 1986.
Diseases of Asparagus in Oklahoma. OSU Extension Facts No. 7646.
Oklahoma State University Cooperative Extension. 4 p.
- Marr, C.W., et al. 1990. Asparagus
Guide. Kansas State University Cooperative Extension, Manhattan,
KS. 4 p.
- Conway, Kenneth E. 1987. Summer
disease control on asparagus ferns can mean increased profit next
year. p. 41-43. In: Proceedings of the 1987 Oklahoma Horticulture
Industries Show, Tulsa, OK.
- Johnson, D.A. 1990. Effect of crop
debris management on severity of Stemphylium purple spot
of asparagus. Plant Disease. Vol. 74. p. 413-415.
- Personal communication.
- Paine, L., H.C. Harrison and A.C.
Newenhouse. 1995. Establishment of asparagus with living mulch.
Journal of Production Agriculture. Vol. 8, No. 1. p. 1-2.
- Anon. 1990. New reasons to salt
asparagus beds. Countryside. July-August. p. 12.
- Poncavage, Joanna. 1998. Weeds
in asparagus. Organic Gardening. April. p. 18.
- OSU Vegetable Research Station
13711 S. Mingo Rd.
Bixby, OK 74008
918-369-2441
- Dr. Jim Motes, Extension Specialist
(retired)
Department of Horticulture and L.A., OSU
360 Agricultural Hall
Stillwater, OK 74078
405-744-5414
- Holland Transplanter Co.
510 E. 16th St.
Holland, MI 49423
Tel: 800-275-4482
Fax: 616-392-7996
- Rusty’s Ag Sales
412 N. 7th St.
Fairbury, IL 61739
Tel: 800-373-2809
- Hardenburg, Robert E., Alley
E. Watada, and Chien Yi Wang. 1986. The Commercial Storage of
Fruits, Vegetables, and Florist and Nursery Stocks. Agriculture
Handbook No. 66. USDA/ Agriculture Research Service. p. 52.
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Enclosures
Anon. 2000. Work efficiency tips can help vegetable growers. American
Small Farm. April. p. 28.
Anon. 2000. Healthy Farmers, Health Profits project to work with
berry growers. Northland Berry News. Summer. p. 13.
Anon. 2000. One-row riding “strawberry picker.” Farm
Show. May-June. p. 18.
Anon. 2000. Agricultural Alternatives: Asparagus Production. Pennsylvania
State University, University Park, PA. 6 p.
Bird, Christopher O. 1998. Growing white asparagus. National Gardening.
January-February. p. 78, 80, 81, 82.
Cantaluppi, Carl J. 1994. Getting started in asparagus. p. 11.
In: Proceedings of the 1994 Ohio Asparagus, Strawberry, and Small
Fruit Schools. Ohio State University Misc. Publ. No. 94-1. p. 11-21.
Kren, Lou. 1994. Homemade harvesters. American Vegetable Grower.
May. p. 19-21.
Makus, Don and A.R. Gonzales. 1991. White Asparagus Production
Using Opaque Plastic Covers. Arkansas Farm Research. March-April.
p. 10-11.
Motes, J. E. 1987. Asparagus Harvesting Strategy for Maximum Profit.
Department of Horticulture and L.A., Oklahoma State University Extension.
1 p.
Mullen, Bob and Bob Kasmire. No date. Post-Harvest Handling of
Fresh Market Asparagus, A Brief Review. Reprinted by Department
of Horticulture and L.A., Oklahoma State University. 2 p.
Sanders, Douglas C. 2001. Asparagus Crown Production. North Carolina
State University, Raleigh, NC. 2 p.
Sanders, Douglas C. 2001. Commercial Asparagus Production. North
Carolina State University, Raleigh, NC. 6 p.
Thelander, Mike. 1988. Growing fresh market asparagus. p. 23-31.
In: Proceedings of the 1988 Illinois Asparagus School. Horticulture
Series 73. University of Illinois Cooperative Extension Service,
Urbana-Champaign, IL. Horticulture Series 73.
Walters, Pat. 1998. Asparagus on small acreage. AgVentures. October-November.
p. 27-29.
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Resources
Growing Asparagus in California is University of California
Extension Leaflet No. 21447. It describes climatic and soil requirements,
asparagus varieties, planting methods, caring for the established
plantation, pest management, harvesting, and post-harvest handling.
This 24-page leaflet is available for $2.50; checks payable to UC
Regents. Contact:
ANR Publications
University of California
6701 San Pablo Avenue
Oakland, CA 94608-1239
510-642-2431
Asparagus Production, Management, and Marketing is Ohio
State University Extension Bulletin No. 826. It contains current
information on asparagus varieties, planting techniques, white asparagus
culture, and general management and harvesting procedures. This
25-page bulletin is available for $4.75; checks payable to The Ohio
State University. Contact:
Extension Media Distribution Office
The Ohio State University
385 Kottman Hall, 2021 Coffey Road
Columbus, OH 43210-1607
614-292-1607
The Ohio (formerly Illinois) Asparagus School, organized by Carl
Cantaluppi (formerly of the Piketon Research & Extension Center
in South-Central Ohio) is an annual growers school. The Proceedings
of the Ohio Asparagus School, and back issues of The Proceedings
of the Illinois Asparagus School are available for purchase
through the Piketon Research Center. Contact:
OSU-Piketon Research & Extension Center
1864 Shyville Rd.
Piketon, OH 45661
740-289-2071
Asparagus: Pest Management Guidelines. 1994. University
of California IPM *IMPACT* Pest Management Guidelines. UCPMG Publication
No. 32. 23 p.
The University of California has produced quite a few manuals
on IPM for field, vegetable, and fruit crops. The *IMPACT* series
of publications contain a summary of IPM material in the IMPACT
IPM Database. This publication on asparagus addresses: Insects,
Diseases, and Weeds. Each entry includes: Description of the Pest;
Damage; Cultural Control; Biological Control; Organically Acceptable
Methods; Chemical Controls; and When to Treat. Contact one of
the addresses below for ordering information. This publication
can also be downloaded from the internet at www.ipm.ucdavis.edu/PMG/selectnewpest.asparagus.html.
UC IPM Education and Publications
University of California
Davis, CA 95616-8620
530-752-7691
Statewide IPM Project
University of California
Davis, CA 95616-8621
530-752-8350
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Web sites
http://aggie-horticulture.tamu.edu/extension/easygardening/asparagus/asparagus.html
Great information about all aspects of asparagus
from planting to harvest.
www.msue.msu.edu/msue/iac/agnic/asparagus.html
Highly informative site on asparagus including an asparagus
reference service.
www.plantmanagementnetwork.org/pub/php/review/asparagus/
Contains information on the economically important diseases
of asparagus.
www.ext.nodak.edu/extnews/askext/vegetabl/1121.htm
Addresses the various aspects of growing asparagus.
http://agbiopubs.sdstate.edu/articles/ExEx6009.pdf
(PDF / 259KB)
A Cooperative Extension publication from South Dakota.
www.orst.edu/Dept/NWREC/asparagu.html
Deals with a myriad of asparagus terms and varieties.
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Additional Resources
Sources for the “Purple Passion” Asparagus Variety
California Asparagus Seed and Transplants, Inc.
2815 Anza Ave.
Davis, CA 95616
530-753-2437
Pendleton’s Country Market
1446 E. 1850th Rd.
Lawrence, KS 66046
785-843-1409
Sources for Asparagus Seed
Rupp Seeds, Inc.
17919 Rd. B
Wauseon, OH 43567
419-665-2658
Nourse Farms, Inc.
41 River Rd. South
Deerfield, MA 01373
413-665-2658
Jersey Asparagus Farms,
Inc.
105 Porchtown Rd.
Pittsgrove, NJ 08318
800-499-0013
Organic Asparagus Production
By George Kuepper & Raeven Thomas
NCAT Agriculture Specialists
Cole Loeffler, HTML Production
CT 100
Slot 144
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