Asparagus Weed Control: Tips For Using Salt On Asparagus Weeds

By: Bonnie L. Grant, Certified Urban Agriculturist

An old method of controlling weeds in the asparagus patch was to pour the water from an ice cream maker over the bed. The salty water did indeed limit the weeds but over time it collects in the soil and can cause problems. Know how to use salt on asparagus and when too much is too much for these delicious plants.

Using Salt on Asparagus Weeds

One of the first spring vegetables is asparagus. The crisp spears are perfect in a variety of preparations and adapt well to a host of cuisine types. Asparagus are perennials which grow from crowns planted 6 to 8 inches (15-20 cm.) beneath the soil surface. This means deep hoeing is not an option to get rid of weeds.

Using salt for weed control is an old farm tradition, and while the high salinity does kill some annual weeds, persistent perennial weeds may be resistant and the practice leaves an excess of salt in the bed which can be detrimental to the asparagus. However, there are other safer methods than using salt on asparagus weeds.

It is not a good idea to use salt in asparagus soil unless you plan on testing the salinity of the soil annually and stop when it begins to reach high levels. High levels of salt in asparagus soil can impede percolation and water drainage. Over time the saline will build up to a level that will even kill a salt tolerant plant such as asparagus. That will destroy your crop of tender spears and waste the three years you had to wait for your bed to produce well.

Other Methods of Asparagus Weed Control

Our ancestral farmers knew how to use salt on asparagus and when to stop the practice to prevent poisoning the soil. Today, we have several different tools available to us and do not have to resort to salt for weed control.

Hand Pulling Weeds

You were given hands for a reason. One of the simplest methods of weed control that is non-toxic and creates no buildup of salt or other chemicals in the soil is hand weeding. It is even organic! Hand weeding is also effective, but it doesn’t work quite as well in large asparagus beds.

Light tilling can be done in early spring before the spears have begun to show. The shoots are quick growers and using salt on asparagus weeds can burn the tender new spears. Hand weeding is tedious, but useful to most home gardeners. The tough part is getting the roots of perennial weeds, but even removing the greenery will eventually weaken the root and kill the weed over time.

Using Herbicides for Asparagus Weeds

Modern farm practices include the use of pre-emergent herbicides to prevent weed seeds from sprouting. Corn gluten meal is non-toxic and has pre-emergent properties. It may safely be used on the entire bed every four weeks. Use caution when applying to beds with germinating seeds, as it will impede sprouting.

Another method is the use of post emergent herbicides. Use it after the last harvest when no spears are above the soil or in early spring broadcast it over the entire bed before shoots appear. Make sure no herbicide contacts the plant material or you could kill the crowns, as the products are systemic and will leach through the vascular system to the root. It is safe to use as long as the product only contacts soil, and will remain in the soil to kill sprouting weeds.

Any of these methods is safer and more effective than salt in asparagus soil.

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When To Fertilize Asparagus?

Asparagus is one vegetable I’ve always enjoyed because of its productivity rate. However, in my experience, I needed to fertilize it at the right time to get the best yield.

After careful research and a few years of trial & error, I want to present you with some useful information of when to fertilize asparagus.

Are you looking to understand when to fertilize asparagus? We’ve got you covered. In this article, I round up the main points of my research for you.

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Asparagus Salt Water

Can you sprinkle rock salt on the base of asparagus to keep weeds out of it?

Asparagus has a higher tolerance for salt in the soil that many weeds do, so an old practice used to be to pour the salty water from the ice cream maker over the asparagus bed to kill weeds. However we don't recommend this now, because too much salt in the soil will eventually kill the asparagus, too! The best option is to use mulch and Preen to control the annual weeds.

Or here's another technique used by commercial growers. At the last harvest of the season cut down all the spears, so there's no foliage or anything above the ground. Rake the soil over the top of the spears. Then overspray the entire planting with glyphosate (RoundUp). Glyphosate becomes bound by the soil particles when it hits them, so will not damage the crowns below ground. This will control annuals and tough perennial weeds. The spears will then re-emerge from the soil and not be damaged by the glyphosate at all. Apply some mulch to help with the weed control, then Preen.

MSU Extension

Cool, wet spring may increase weed control challenges in asparagus.

Weeds are emerging in asparagus fields even if asparagus is delayed by cool weather. Asparagus growers have an opportunity to prepare and implement a season-long weed control program to kill emerged weeds and suppress weed germination. Many persistent weeds require several herbicide applications to maintain control throughout the asparagus growing season (April through September).

Winter annual and perennial weeds have emerged and are growing well. Quackgrass, annual bluegrass, yellow rocket, dandelion, horseweed (marestail), mouseear cress, henbit, purple deadnettle, white campion and wild carrot are common early-season weeds. These weeds should be killed with foliar-active post-emergence herbicides either now or when applying the pre-emergence herbicides. Glyphosate (Roundup), paraquat (Gramoxone), 2,4-D (Formula 40) and Fusilade are potential choices for killing emerged weeds early in the season.

Quackgrass is not killed easily with glyphosate any time of the year. In early spring, quackgrass is suppressed by glyphosate application but reemerges soon. If quackgrass is the primary spring weed, consider using a high rate of Fusilade DX (1.5 pints per acre) plus crop oil concentrate (COC). A nitrogen (N) source, such as 28 percent liquid N, may enhance fluazifop activity. Reapply Fusilade 14 days later. A combination of glyphosate and Fusilade may improve quackgrass control.

Many overwintering annual broadleaves, winter annuals and seedling perennial broadleaf weeds will be killed with glyphosate applied in the spring. If only very small seedlings have emerged, paraquat should kill most of them. If the field is known to have glyphosate or PS II-resistant broadleaves (e.g., horseweed, pigweeds, lambsquarters), and those species have emerged, consider adding 2,4-D to the glyphosate. If horseweed is the primary broadleaf weed present, include 5-10 fluid ounces of clopyralid (Spur) in the mix. Clopyralid is very active against all composites, such as horseweed, ragweed, dandelion, mayweed and skeletonweed.

Pre-emergence herbicides should be rotated for spring and summer application and year to year. Diuron (Karmex) is a good photosynthesis (PS II) inhibitor with a broad range of activity. Because of the presence of PS II-resistant Powell amaranth (and other resistant pigweeds) in most Michigan asparagus areas, always add another pre-emergence herbicide with a mode of action different from diuron. Good choices are Solicam, Spartan, Dual Magnum, Prowl H2O or Callisto. During the growing season, note the weeds that emerge and survive. For the residual application after harvest, select two herbicides with modes of action different from those used in the spring.

During harvest, growers may apply halosulfuron (Sandea), linuron (Lorox), 2,4-D (Formula 40), dicamba (Clarity) or clopyralid (Spur) to control broadleaves, and fluazifop (Fusilade), sethoxydim (Poast) or clethodim (Select Max) to control grasses. With correct use of these herbicides, few weeds should survive. Check labels for pre-harvest intervals for all herbicides.

Growers have many options for weed control in asparagus. With knowledge of weeds present and herbicides registered for use in asparagus, growers should be able to control most weeds in asparagus throughout the growing season.

Current vegetable herbicide recommendations are available in Michigan State University Extension Bulletin E0433, “Weed Control Guide for Vegetable Crops.”

This article was published by Michigan State University Extension. For more information, visit To have a digest of information delivered straight to your email inbox, visit To contact an expert in your area, visit, or call 888-MSUE4MI (888-678-3464).

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Weed Management Options for Asparagus

Photo: Annie Klodd

As we reach the end of asparagus harvest, growers are probably thinking, “Oh great, now I get to get rid of all these weeds.” Late June is a good time to wrap up harvest and clean up the field to make room for fern growth.

This article will discuss weed management from the framework of IWM (Integrated weed management). It will describe cultural and mechanical methods of weed management followed by chemical options.

Because asparagus is a perennial crop that has green tissue from April to December, one of the biggest challenges is managing weeds within the asparagus rows. Growers must look for methods and windows of time for weed management that do not harm the growth of the plant. They also must develop a strategy for perennial weeds such as Canada thistle and quack grass, which thrive in asparagus beds due to the open soil and lack of tillage.

Managing weeds between the rows is much easier in comparison to the rows themselves. Aisles can be kept weed free without the use of herbicides via cultivation, flaming, mulching, or cover crops.

Non-chemical weed management

Cultivation: Cultivation can be used cautiously and at specific times in the rows, when the spears and ferns are not present. Additionally, cultivation can be used throughout the season to eliminate small weeds in the row aisles. Some asparagus producers cultivate the rows in the early spring, after snow melt but before spear emergence. If all spears are harvested below the soil surface at the end of the harvest season, cultivation may also be possible in the rows immediately following the last harvest. At both timings, the cultivation must be very shallow, less than 3 inches, and should be done before new spears start emerging. Understandably, this presents challenges.

Before spear emergence, the main role of spring cultivation is to incorporate fertilizer. However, it can also eliminate winter annual weeds that have started to resume growth. The action of cultivating in the spring can also stimulate growth of weed seeds that were previously buried. Therefore, growers should consider whether it is really necessary to cultivate each spring.

Post-harvest cultivation should be done immediately following the final harvest, and only if spears were harvested below the soil surface. Post-harvest cultivation can uproot small emerged weeds to keep the soil relatively weed free until the ferns become established enough to outcompete weeds. Shallow cultivation is not likely to control thistles or other weeds with taproots and rhizomes, or large established annual weeds.

Cover crops: Rather than cultivating between the rows, asparagus growers can avoid tillage and increase their soil health by planting cover crops in the aisles. Usually, these are perennial cover crop mixes such as fescues, perennial ryegrass, and clover. Annual cover crops may be a good choice for newly planted fields, as they are quicker to establish. More details on cover cropping asparagus will be provided in a future article.

An asparagus field with a perennial cover crop. The spears are easier to see in person! Photo: Annie Klodd

Flaming (propane weeding): Flame weeders, also called propane weeders, emit heat from propane-powered torches that kill weeds by heat. Despite the name “flame weeder” this tool is not meant to burn the weeds. Flame weeds come in many different shapes and sizes, from individual torches on a backpack model, to pull-behind implements for tractors. Flaming can be used carefully within the rows, or in the aisles.

Hand-removal: Despite our best efforts, asparagus production sometimes requires removing weeds by hand. Hand removal comes in when large annual weeds and perennial weeds are too well established to control via shallow cultivation or flaming. It is also necessary to remove weeds in the rows during the peak growing season, when the presence of spears precludes the use of cultivation, flaming, or herbicides. Hand-removal can also be used to eliminate any weeds that escape through cover crops and mulches.

In the absence of herbicides, hand removal is the most effective choice for managing Canada thistle. While thistles can be mowed and cultivated, this cannot easily be done in the rows with enough frequency to control an established thistle population. Flaming has not been shown as an effective tool against thistles or quack grass, as it only burns the tops and does not impact the belowground rhizomes (spreading roots) that these plants use for reproduction. Therefore, growers resort to hand-removal for stubborn perennial weeds as well as large, established annuals.

Canada thistle can be a very aggressive weed in asparagus stands and usually requires either hand removal or herbicides. Photo: Annie Klodd

Mulching: While not a commonly used practice, the aisles between the rows can be mulched using wood chips, straw, or landscape fabric in order to smother weeds between rows. Mulch is not recommended in the rows, and it can lead to high pest pressure from asparagus beetle and asparagus aphid.

Herbicide Options for Asparagus

Herbicide Types and Application Timings

There are legitimate reasons why many growers choose to use herbicides (either synthetic or organic) in asparagus. First, many Minnesota asparagus growers are also growing strawberries, and therefore are too busy in late June to spend a considerable amount of time with weed management after asparagus harvest is complete. Just a couple of well-timed herbicide applications drastically reduces the amount of time spent on good weed management. Secondly, using herbicides reduces the need to cultivate, thereby presenting an opportunity to move the system toward no-till or minimal-till and improving soil health.

A wide selection of herbicides can be applied before, during, or after the harvest. There are multiple options for pre-emergent and post-emergent herbicides labeled for asparagus. While post-emergent herbicides target actively growing weeds, pre-emergent herbicides have soil activity that prevents new weeds from emerging. The problems facing the grower are choosing an application method that complements the operation and choosing a chemical and rate that will control weeds after harvest for the duration of the growing season.

Herbicide application timings include:
• Before planting crowns
• Early spring before spears emerge
• After final harvest but before ferns grow
• During harvest after cutting all emerged spears*
• To ferns during the post-harvest period

*Because asparagus spears continually emerge and are harvested frequently during the harvest period, herbicide application during this time is mostly not possible. The exception to this is that select products can be applied during harvest if all spears are harvested first, regardless of size.

When to use pre-emergent herbicides: The use of a pre-emergent herbicide in the spring is beneficial for this crop, because it reduces the amount of weeds emerging during the busy harvest period. A second pre-emergent application may be done after harvest, to keep weeds down until the ferns are large enough to outcompete them.

When to use post-emergent herbicides: Post-emergent herbicides can be used in the early spring to kill winter annual weeds, and after harvest to kill weeds that came up during harvest. In general, weeds are more susceptible to herbicide control when they are less than six inches tall. Larger weeds will still require hand removal, as described above.

Organic Herbicides:

Ammonium nonanoate: an organic, non-selective post-emergent herbicide. It can be used in the rows before planting new crowns, or before spear emergence in mature stands. It has effectiveness on many annual weed species, and will suppress growth of some perennial weeds. More concentrated solutions should be used for larger weeds. See the label for more information.

Caprylic or capric acid: an organic, non-selective post-emergent herbicide. Like ammonium nonanoate, it can be used in the rows before planting new crowns, or before spear emergence in mature stands to kill actively growing weeds. It has some activity on most annual weeds and suppresses growth of perennials. For best results, leaves should be thoroughly wetted. See the label for more information.

Below is a table of herbicides labeled for use in asparagus. The table shows when each product can be used, whether it is a pre-emergent or post-emergent herbicide, what types of weeds it targets, and whether it can be used on new plantings. This table is found in the Midwest Vegetable Production Guide for Commercial Growers, page 92.

New Crown Plantings

Good weed management is critical for establishing high yielding, healthy new asparagus beds. The newly planted crowns have very small root systems, so just a few weeds around each plant can drastically decrease fern growth and subsequent yields.

As described previously, most new asparagus production fields are established by planting one-year-old nursery grown asparagus crowns into deep furrows. Since the first new shoots take several weeks to emerge and grow to a size that can be safely cultivated, weeds in the furrow may become too large to cultivate. Therefore, a pre-emergence herbicide with long residual activity will reduce early season weed populations and decrease the number of cultivations needed to keep fields weed-free.

Preventing Herbicide Injury

Herbicide injury can occur to asparagus stands if herbicides are applied against the label guidelines. Common causes of herbicide injury include exceeding labeled rates, failing to calibrate the sprayer before spraying, and spraying at a time in the season that is not permitted by the label.

For example, while halsulfuron (i.e. Sandea) can be applied after harvest, it should not be broadcast over the rows it must be applied using a directed or shielded sprayer to prevent direct damage to ferns. Additionally, if broadleaf herbicides such as dicamba or 2,4-D are applied in the spring slightly too late, once spears start to emerge, that can cause spear damage.

Another common scenario for herbicide injury is when part of the field finishes harvest and starts producing ferns before the whole field is ready for the final harvest. In this case, growers may mow the entire field a few inches above the soil surface, and then apply a labeled herbicide before ferns begin to grow back.

Herbicide damage in one year can decrease yield the following year by injuring the ferns and crowns. If herbicide damage is severe, such as if it killed a significant portion of the ferns, the grower may consider doing a reduced harvest the following year in order to allow the stand to recover. Monitor rate of spear emergence the following spring to determine if this is necessary.

Answers to Frequently Asked Asparagus Questions

Asparagus is one of the most popular vegetables in the home garden. If given good care, an asparagus planting may be productive for 15 or more years. Answers to several frequently asked questions on asparagus care and maintenance are provided below.

When and how do I plant an asparagus bed?

A. Early spring (April) is the best time to plant an asparagus bed in Iowa. Since asparagus is a perennial crop, carefully consider possible sites. Asparagus performs best in well-drained soils in full sun. In poorly drained sites, raised beds may be a solution. Avoid shady sites near large trees and buildings.

Asparagus can be grown from seeds. However, asparagus is most commonly established by planting one-year-old asparagus plants or crowns. Asparagus crowns should be planted in shallow trenches or furrows. The planting depth depends on the soil type. Asparagus crowns should be planted 6 to 8 inches deep in light, sandy soils, but only 4 inches deep in heavier soils. A small amount of manure can be worked into the soil at the bottom of the trench before planting. Space the crowns 12 to 18 inches apart in rows that are 4 to 5 feet apart. Spread the roots out in the trench with the buds pointing upward. After planting, completely fill in the trench with soil. (Though commonly done in the past, it's not necessary to gradually fill in the furrow as the plants grow.) Male hybrid asparagus varieties are more productive and longer-lived than other varieties. Suggested male asparagus varieties for Iowa include Jersey Giant, Jersey Knight, and Jersey King.

Is it possible to move an established asparagus bed?

A. The roots of established asparagus plants are deep and quite extensive. As a result, transplanting attempts are usually unsuccessful. Large, old plants will be severely injured during the transplanting procedure. Some may actually die. Those that survive may never produce a good crop. The best way to establish an asparagus planting is to purchase one-year-old plants or crowns from a garden center or mail-order nursery.

When can I start harvesting my asparagus?

A. Asparagus plants should be allowed to become well established before any spears are harvested. No spears should be harvested during the first growing season. Asparagus can be harvested over a three to four week period during its second growing season. In following years, asparagus plantings can be harvested until early to mid-June. Harvest asparagus by cutting or snapping the spears when they reach a height of 6 to 8 inches.

When should I stop harvesting asparagus?

A. Discontinue harvesting well established asparagus plantings in early June in southern Iowa and mid-June in northern portions of the state. If harvested over a longer period, the plants may be weakened and less productive in future years. Allow the asparagus stalks to grow after the last harvest.

When should I fertilize my asparagus bed?

A. Asparagus can be fertilized in early spring before the spears emerge. An application of 1 to 1.5 pounds of an all-purpose garden fertilizer, such as 10-10-10, per 100 square feet should be adequate. Asparagus can also be fertilized after the last harvest in June. Using a nitrogen fertilizer, apply .10 pound of actual nitrogen per 100 square feet. For example, an application of .3 pound of ammonium nitrate (34-0-0) per 100 square feet will supply .10 pound of actual nitrogen.

How do I control weeds in my asparagus planting?

A. The best way to control weeds in a home asparagus planting is by hoeing or tilling. Hoe or till the planting periodically in spring and early summer. Cultivate lightly to avoid damage to emerging spears.

How do I control perennial grasses in my asparagus bed?

A. Because of their extensive root systems, perennial grasses can be difficult to control in asparagus. Hoeing or tilling will simply not work. The best option is to spot treat with glyphosate (Roundup) immediately after the last harvest of the season. During the last harvest, cut or snap off all asparagus spears at the soil surface. Then immediately spot treat the grass-infested areas with Roundup. Do not allow Roundup to get on any emerged asparagus growth as injury or death may result.

Is salt beneficial to asparagus?

A. Applying salt to an asparagus planting is not beneficial. In years past, some gardeners used salt to control weeds in asparagus. However, salt is not effective in controlling many weeds, especially grasses. Plus, continued use of salt may result in high salt levels in the soil. High levels of salt may actually damage the asparagus planting. In the home garden, shallow hoeing or tilling is the best way to control most weeds.

When can the asparagus foliage be cut back?

A. It's imperative not to cut back the asparagus foliage while it is still green. To produce a good crop next spring, the asparagus plants must manufacture and store adequate levels of food in their roots and crowns. The dead (brown) tops can be cut back in late fall. However, it's generally recommended that the dead top growth be allowed to stand over winter. The dead growth will catch and hold snow. The snow insulates the asparagus crowns and also provides moisture.

This article originally appeared in the 3/26/2004 issue.

Watch the video: How to Keep Your Asparagus Bed Weed Free

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