It is with great pleasure for us to introduce a new column, “Grower Guidelines” by Carl Cantaluppi. Carl has worked in Cooperative Extension for 36 years in the Northeast, Southeast and Midwest. He will bring timely topics about fruit and vegetable production based on his experience.
Asparagus facts and pointers
One of the crops I have worked with extensively is asparagus. Gone are the myths about asparagus and we now have extremely productive varieties which can be easily grown.
Myth: Asparagus needs to be planted deep for good production
Research shows the deeper asparagus crowns are planted (eight inches or more), large diameter spears are produced but the total yield is reduced. Shallow-planted asparagus (four inches) produces smaller diameter spears but the total yield is greater. Plant asparagus six inches deep in sandy soils and five inches deep in clay soils.
Myth: Asparagus is a heavy feeder of nitrogen
Research has shown when nitrogen was applied to asparagus — pre-harvest, post-harvest, and a combination of the two — yields were actually less. Nitrogen is essential for good fern growth but it does not seem to influence spear yield.
Myth: Asparagus should not be harvested during the second year
It needs to develop food reserves in the crown and harvesting too early would reduce the food reserves and severely reduce future yields. Research done by myself and others have shown plants were not weakened when spears were harvested during the second year. The average spear weight was found to be significantly greater in plants which were harvested the second year. The increase in spear production may be due to the release of buds which would normally be suppressed by older shoots which were not harvested. It’s fine to harvest two to three times during the second year.
The botany of an asparagus plant
Traditional asparagus varieties are dioecious, meaning they have male and female reproductive structures on separate plants. These are also referred to as “open-pollinated.” Female plants produce spears and also produce seed when the plant is in the fern stage. The production of seed diverts photosynthetic energy from spear production and reduces the yield of spears. The seeds fall to the ground and germinate, creating an undesirable asparagus seedling weed problem. Male asparagus plants produce about 50 percent more spears than female plants, not having to expend energy to produce seed.
Dr. Howard Ellison, former asparagus breeder at Rutgers University in New Jersey, observed although asparagus produces both male and female plants, about one in 500 male plants will produce male flowers and a few flowers with functional male and female parts. By selfing flowers on these plants, called hermaphrodites, Ellison produced his first male hybrid.
These male hybrids have tolerance to asparagus rust and Fusarium crown rot, two major fungus diseases which affect asparagus. With ample rainfall, these hybrids can attain a fern height of over five feet in one growing season.
The New Jersey male hybrids have wide geographic adaptability and have yielded well in several variety trials across the eastern and Midwest U.S. Some of the more popular New Jersey male hybrids include Jersey Giant, Jersey Supreme, Jersey King, Jersey Gem and Jersey Knight.
Open-pollinated varieties include Mary Washington, Martha Washington, and Waltham Washington. These varieties were developed by breeding and selection work done by the U.S. Department of Agriculture, in cooperation with the Massachusetts Agricultural Experiment Station and others, for the purpose of obtaining varieties resistant to asparagus rust. These varieties are no longer recommended for commercial production.
The Viking KB3 is an open-pollinated selection of Mary Washington developed in Ontario, Canada. It yields higher than Mary Washington. In general, the open-pollinated varieties produce about 1/3 the yield of the New Jersey hybrids.
Organically grown asparagus
One of the most difficult things to accomplish is to try to grow asparagus organically. Fungus diseases such as rust and Cercospora needle blight can be destructive if not kept in check with timely fungicide applications.
Weed control is also very important in obtaining good asparagus yields. Failure to control weeds during the planting year will severely impact yields in the following year. Hand hoeing and shallow cultivation can be done to control weeds but is very time consuming. For these reasons, herbicides are needed for successful production of asparagus.
Soil cultivation around asparagus plants can cause damage to the roots which can predispose them to root rotting fungus diseases. Also, research has shown tillage in asparagus reduces yields with the yield differences between tilled and no-till plots becoming more significant over time. In addition, asparagus weed seedlings from female plants can be controlled more effectively with a no-till system than when soil is tilled. Tilling the soil disperses asparagus seeds and encourages quick germination.
When growing male hybrid varieties, growers will find a small percentage of female plants growing in the field. Getting crowns which are 100 percent male is not possible and a grower will always have some female plants. Should a grower cut off the ferns which are producing the red berries? No. By mowing the dead fern growth off about one month before new spears are produced in the spring, the berries will fall and land on the shredded fern and reduce soil contact, thereby inhibiting germination.
Soil preparation before planting asparagus
Asparagus grows and yields best in a deep, well-drained sandy loam soil but will tolerate heavier soils as long as the soil has good internal drainage and the water table does not come within four feet of the surface.
It is important to eliminate all perennial weed problems at least one year before planting. This can be done effectively by treating the actively growing weeds with a non-selective herbicide. Another way to reduce weed populations and help build soil organic matter is to prepare the field at least one year in advance. This can be done by planting a cover crop such as clover or an early maturing soybean variety. The soybeans can then be harvested or clover can be chopped and plowed down and seeded to winter wheat or rye at three to four bushels per acre in the fall before planting asparagus.
Soil test to determine pH and fertilizer requirements. The ideal pH range for asparagus is between 6.7-7.0. Asparagus does not tolerate acid soils and will not grow well at a pH of less than 6.0. Also, a fungus disease which contributes to asparagus decline (Fusarium crown and root rot) survives better at a low pH. Liming the soil to bring the pH up to 7.0-7.5 would reduce the survivability of Fusarium, especially if asparagus has been grown there previously. Phosphorous and potassium should be provided so the soil contains 250 lbs. of available phosphorus and 300 lbs. of available potassium per acre. Phosphorus must be incorporated before planting. Also apply 70 lbs. of actual nitrogen per acre.
Asparagus Production from A to Z
Are you now wanting to learn more? Then order a copy of my new asparagus bulletin, “Asparagus Production from A to Z.” It is a comprehensive 68-page regional bulletin which covers the planting, growing, harvesting and marketing of asparagus, including a budget with costs and expected income per acre. The bulletin includes 25 color photos of insects, diseases and planting techniques to aid the grower.
- A detailed study of asparagus varieties
- Results of a 10-year replicated variety trial in North Carolina
- White asparagus production using opaque covers
- Handling, grading and storage
- Marketing methods
- Estimating spear growth of asparagus as affected by temperature
- Yield increases as influenced by judicious fungicide applications
The bulletin is bound with a plastic spiral binder. It sells for $25, including shipping and handling. To order send a check or money order payable to Carl Cantaluppi to:
1222 Grangers Rd.
Selinsgrove, PA 17870