News Column
Tony Bratsch
Extension Educator, Horticulture
Effingham Extension Center
1209 Wenthe Drive
Effingham, IL 62401
Phone: (217) 347-5126
Email: bratsch@uiuc.edu
Kill Date: July 30, 2007
Asparagus Beds Need Attention After the Harvest Ends
June marks the end of asparagus cutting season. Now is the time to think ahead to next year’s
harvest and take measures to improve and maintain vigor in your planting. From now until the first
freeze in the fall, asparagus plants are building and storing reserves, and developing the crown
buds that will become the spring shoots of 2008. The degree of sugar and carbohydrate build-up
achieved this year directly influences the quantity and quality of spears next year.
In weakened asparagus beds, spears become small, thin and spindly. This is often a result of
cutting too long into the early summer in previous years, and not caring properly for the planting.
Usually on a mature, healthy planting, 6 to 8 weeks of cutting is easily tolerated. Low fertility, root
and foliage diseases and insect damage can also weaken the planting and be responsible for poor
production. Though asparagus is winter hardy, with more shallow plantings, severe and sudden
drops in temperatures can damage older crowns. Over time and as plants age, crown depth can
decrease as the crowns slowly “creep” upward and become more exposed to sudden soil freezing
events.
Reduced spear size is not always related to adverse growing conditions. It is also related to the sex
of the plant. Asparagus plants are male and female. Female plants have thinner spears and produce
red berries. Male plants flower also, but do not fruit, and thus expend less energy on reproduction,
instead developing thicker spears, though usually fewer in number.
As male plants are preferable, how can the gardener select for them? With new crowns or seed of
older varieties such as ‘Mary Washington’, usually a mix of male and female plants occurs, but
there is no way to tell the sex of the plants until they flower. Newer “all male” hybrids are now
available on the market, and are being widely planted. Developed by breeders in New Jersey, the
series of asparagus varieties with ‘Jersey’ in the name are available in most garden catalogs. Look
for varieties such as ‘Jersey Knight’, ‘Jersey Giant’, ‘Jersey Supreme and ‘Jersey King’, all of
which perform well in the Midwest. In addition to having larger spears, these hybrids have
considerable disease tolerance to root rotting and foliar rust diseases.
New asparagus beds take several years before abundant, thick spears are produced. To maintain
production, good management of the foliage during the summer and fall months is required, with a
focus on providing adequate fertility, managing foliar disease and insect damage, and limiting
weed pressure that competes with the asparagus plant. A well-planted and maintained asparagus
bed should be productive for 20 to 30 years or more.
To maintain fertility, a surface application of fertilizer should be applied after the last cutting is
made. Apply well rotted compost or manure, covering the soil with 1 to 2 inches deep in a two foot
wide area over the row. If manure is not available, apply commercial fertilizer such as 12-12-12
using a cup of material for every 10 feet of row. Avoid contact with emerging shoots and stems to
avoid burning. When manure is used, cut chemical fertilizer amounts in half.
Research has shown that asparagus responds variably to fertilizer applications. If vigorous growth
is occurring, a lighter fertilizer application may be adequate. It may be more efficient to apply
some fertilizer in the very early spring prior to first spear emergence, and again after harvest,
especially on lighter soil types. Keep in mind that spring and post-harvest fertilizer application will
not improve the current season’s crop. Instead it increases growth and vigor of the tops or 'ferns'
from now until fall, improving next year’s crop.
Good weed control is also essential to maintain vigor in a planting. Herbicides containing
trifluralin (Preen™) can be used for control of annual weeds in larger plantings. At one time salt
was commonly used to kill weeds in asparagus. Because of its origins near the Mediterranean Sea,
asparagus is fairly salt tolerant. However prolonged use of salt leads to deterioration of the
physical properties of the soil and a reduction in growth, and is not recommended.
Asparagus beetle is a common insect pest of asparagus, as well as Japanese beetles. They should
be kept under control for maximum plant growth and production. Insecticides such as carbaryl
(Sevin™) and malathion (Fertilome Malacide™) are listed for use on asparagus. Apply when
feeding and presence of the beetles is noted.
There are also foliar diseases (rust and leaf spot) that can brown and discolor foliage, reducing the
capacity of the plant to photosynthesize and build reserves. As noted, the hybrid varieties have
some level of resistance. Use a fungicide containing chlorothalonil (Daconil™) at monthly
intervals after harvest to help suppress these diseases. Because hybrid plants are larger, initial
spacing at planting can be wider (5’-6’ wide rows, plants 18-24” apart), than non-hybrid plants.
This not only allows more room for the plants, but increases air movement in the planting which
helps reduce foliar disease.
Asparagus is an easy and rewarding crop to grow, requiring minimal maintenance to ensure a
successful crop from year to year. Attention to fern care during the summer months will return a
plentiful harvest of spears next spring. For more information of asparagus and other vegetable crop
growing, check out the University of Illinois publication “Vegetable Gardening in the Midwest”,
available from your local county Extension office or visit the U of I Extension website “Watch
your Garden Grow” at: http://www.urbanext.uiuc.edu/veggies/.