In order to kill weeds in asparagus beds, apply salt or a weed killer in spring or fall, when asparagus is dormant. To prevent new weeds from sprouting, use a pre-emergent herbicide, such as Preen or Corn Gluten Meal in spring. Top the soil in your asparagus bed with 3–4 inches of mulch to keep weeds out. Don’t worry, your asparagus spears will shoot up through the mulch.
How to Kill Weeds in Asparagus Patch
It may seem like a daunting task to reclaim an overgrown asparagus patch, but there are several tried-and-true methods for killing weeds in asparagus and maintaining a healthy asparagus bed.
Salting Asparagus Beds
Salting asparagus beds is a natural tactic for killing weeds and preventing their return. Asparagus is very salt-tolerant and can grow in soils with higher saline levels than most plants (including weeds). One trick for asparagus cultivation is to lay seaweed as a winter fertilizer and ground cover—it introduces both salt and nutrients to the soil as it decomposes.
If you don’t have access to seaweed, adding salt directly to the soil will be just as effective., Whether it’s rock salt, table salt, or sea salt, it all works. Apply up to 1 pound of salt per each 10-foot row of asparagus each year. Keep in mind, an overabundance of salt can eventually harm asparagus. If the ground has become compacted and shows white traces of salt when it’s dry, it’s a good idea to cease salting the ground for a year or two.
Exercise caution when applying salt to asparagus beds. Much like the weeds you’re trying to kill, other garden plants don’t tolerate salt well. If there’s a risk of water runoff affecting desirable grass or other plants, refrain from using salt.
Manually Removing Weeds
Hand weeding can be laborious, time-consuming work. The good news is, you can add some tools to your arsenal to make this tactic faster and more efficient.
Asparagus crowns are planted 6–8 inches below the soil, and between fall and spring, the plant dies back to the crown. During this time of dormancy, you can manually remove weeds by hoeing at a depth of 3–4 inches or even by carefully tilling the earth at this depth. This is much faster than pulling weeds individually by hand.
By taking advantage of the dormancy of your asparagus plants, you can use more aggressive measures to get rid of weeds by hand.
Asparagus beds are one of the absolute best places to use mulch. You can spread a thick layer of mulch (anything from 3 inches all the way up to 6 inches) and your asparagus will spear up through the mulch in spring. At the same time, this mulch layer will keep the ground moist, maintain healthy soil temperatures, and discourage weeds from taking root.
A thick layer of wood or bark mulch is essential for an asparagus bed, as it provides benefits for your plants and is a simple way to keep weeds out.
Herbicides for Asparagus
Emergent Weed Killers
Because asparagus is a perennial plant with long periods of dormancy where it dies back to the “crown,” several inches below the topsoil, it affords the opportunity to use powerful weed killers without risking harm to your asparagus plants. We recommend spraying the entire bed with a Glyphosate-based weed killer, such as RoundUp, at this time. Alternatively, you can use a natural, vinegar-based weed killer.
The best times to use weed killers on asparagus beds are in spring before the asparagus has sprouted, or in fall, after the ferns have died back and been removed. During these times, you can use weed killers in your asparagus bed without risking harm to the asparagus itself!
Pre-Emergent Weed Killers
Do you know what’s better than killing weeds in your asparagus bed? Stopping them before they start. In spring, before your asparagus sprouts, apply a pre-emergent weed killer. You can use chemical pre-emergents at this time, or apply Corn Gluten Meal, a natural corn byproduct that dries out weed seedlings. Either of these measures will prevent weeds from coming up without harming your asparagus plants.
When applying any pre-emergent weed killers to your asparagus bed, make sure to rake mulch or any other ground covering to the side so you apply your weed killer directly to the soil. After application, rake the mulch back into place.
Can You Use Preen in an Asparagus Bed?
Preen is a chemical pre-emergent weed killer that is safe to use on asparagus beds. It targets weed seedlings and kills them before they sprout, but won’t harm your mature asparagus plants.
Make sure to apply Preen in early spring. It won’t kill any sprouted weeds but will keep new ones from popping up. When applied early, using Preen on asparagus beds is a very good option for weed control.
Will Roundup Kill Asparagus?
Roundup is a Glyphosate-based product, meaning it will kill any actively growing plant it is sprayed on. If you spray it on asparagus beds with actively growing spears or ferns, you will kill the asparagus along with the weeds.
However, you can apply RoundUp to your asparagus bed in spring (before the asparagus has sprouted) or in fall (after you have removed asparagus ferns). There’s a good chance you’ll still have actively growing weeds in your asparagus bed at these times of the year. Spray them with RoundUp while your asparagus is dormant and you’ll kill the weeds without harming your asparagus.
Weed Control for Asparagus
Weed control for asparagus can be accomplished through several methods: salting, hand weeding, hoeing, tilling, weed killers, and even pre-emergent herbicides. The key to these methods is to attack the weeds during the period of dormancy between fall and spring, when asparagus is dormant, with the living “crown” sleeping 6–8 inches below the topsoil. At this time, you can go all out killing weeds and reclaim even the most overgrown asparagus bed.
Once weeding is complete, top your asparagus bed off with a thick layer of mulch to ensure you maintain a food-producing, weed-free haven in your garden.