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Asparagus Weed Control
submitted by Sarah Browning, UNL Extension Educator
Asparagus Weed Control: Controlling weeds in a home or acreage asparagus planting can be difficult, but it is a necessary step toward maintaining a high-yielding planting. Since asparagus is a perennial crop, it's not possible for home gardeners to till or plow the planting area to eliminate weeds. However, there are several other techniques that can help to successfully control problem weeds.
Asparagus overwinters each year as a dormant crown of roots, with all the summer's foliage and stems dying back to the crown. If planted correctly, the crown is initially located approximately 6-8 inches deep in the soil, but it will grow each year enlarging in both width and height; meaning that an asparagus crown can expand upward in the soil profile over time. It's important to keep this depth in mind and the fact that no living growth remains above ground during the dormant season as we look various methods of control.
Mechanical Control: In small plantings, mechanical removal of weeds can be accomplished by hoeing. This is easy to do in early spring, before new spears begin to emerge, without danger of damage to the plants. In larger plantings very shallow tilling, only about 3 to 4 inches deep, will help eliminate weeds in early spring before new growth begins.
Cultural Control: Mulch, in conjunction with hoeing or tilling, helps maintain your weed control. Apply 3 to 4 inches of an organic mulch, such as wood chips, grass clippings, compost or clean straw. It will prevent germination of new weeds, minimize soil temperature fluctuations in summer and help preserve soil moisture.
Herbicidal Weed Control: Applications of a pre-emergent herbicide can be used to control annual weeds, like crabgrass and foxtail, in the asparagus planting. One product, which has the added benefit of being organic, is corn gluten meal and can be found in Preen Vegetable Garden Weed Preventer, as well as other products. Corn gluten meal is a by-product of corn processing and contains 10% nitrogen, along with its pre-emergent properties. Apply it every four weeks at labeled rates throughout the asparagus planting, but be careful not to apply it to other areas of the vegetable garden where you will be planting seeds.
Post emergent weed control can be achieved with glyphosate and paraquat, both non-selective herbicides with no soil residual activity that can be used in asparagus. Glyphosate is systemic and works best at controlling perennial weeds. It can be broadcast over the entire planting area in early spring before new asparagus grown emerges or after the last harvest. Snap all spears 1/2 inch below the soil line, so no spears are above ground, then overspray the planting area.
Paraquat is a contact, non-systemic herbicide that kills the growing shoots of weeds. It works best for controlling newly emerging annual weeds in early spring before your asparagus has started to grow.
When using herbicide, always read and follow the label directions for personal protective equipment and application rates. Pay special attention to the pre-harvest interval, or the amount of time you must wait after a pesticide application before harvesting again.
Do Not Use Salt!: An old recommendation for asparagus weed control involved the application of salt, by pouring the salty water from an ice cream maker on the asparagus patch. This provided some weed control because asparagus is deep-rooted and has a higher sodium tolerance than some common weeds. However, salt quickly destroys soil structure resulting in pour water penetration in the soil and will eventually kill the asparagus, too, or move out into nearby sections of your vegetable garden and kill other less salt tolerant vegetables.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office