Will Preen Kill Asparagus

Preen will kill asparagus, and it’s important to know this before you reach for that familiar green bottle.
 
Preen is a popular pre-emergent weed killer, but it doesn’t distinguish between weeds and your precious asparagus crowns.
 
In this post, we’ll explore exactly why Preen will kill asparagus, what happens to your plants, and what you can do instead to keep your asparagus bed healthy and weed-free.
 
Let’s dig in.
 

Why Preen Will Kill Asparagus

Preen will kill asparagus because it contains trifluralin or other pre-emergent herbicides that target germinating seeds.
 
Asparagus is a perennial that spreads through both seeds and underground crowns, and Preen doesn’t know the difference between a weed seedling and an asparagus seedling.
 
If you apply Preen to your asparagus bed, you’re putting your entire crop at risk.
 
Here’s why:
 

1. Preen Stops Seed Germination

Preen works by creating a chemical barrier in the top layer of soil.
 
When weed seeds try to sprout, they absorb the herbicide and die before they can grow.
 
But asparagus also reproduces by seed, and those seeds are just as vulnerable.
 
That means Preen will kill asparagus seedlings before they ever break the surface.
 

2. Asparagus Crowns Can Absorb the Chemical

Even if you have mature asparagus crowns, Preen can still cause damage.
 
The roots of asparagus are shallow and feed near the soil surface where Preen sits.
 
Over time, the herbicide can accumulate in the crown and weaken the plant.
 
You might not see immediate death, but you’ll notice fewer spears, thinner stalks, and a slow decline.
 
That’s why Preen will kill asparagus in the long run, even if it doesn’t happen overnight.
 

3. Preen Harms Ferns and Future Harvests

Asparagus ferns are the leafy tops that grow after harvest.
 
They’re essential for photosynthesis and storing energy for next year’s crop.
 
If Preen damages the ferns, the plant can’t produce food, and the crowns starve.
 
This leads to a weak asparagus bed that never fully recovers.
 
So yes, Preen will kill asparagus, or at least ruin your harvest for seasons to come.
 

Signs Preen Has Damaged Your Asparagus

Sometimes damage isn’t obvious right away.
 
Here’s what to look for if you suspect Preen will kill asparagus in your garden:
 

1. Yellowing or Brown Ferns

Healthy asparagus ferns are bright green and feathery.
 
If they turn yellow, brown, or crispy before fall, Preen may be the culprit.
 
The herbicide interferes with nutrient uptake and causes stress.
 

2. Fewer Spears in Spring

If your asparagus bed produces fewer spears than usual, that’s a red flag.
 
Preen will kill asparagus productivity by weakening the crowns over winter.
 
You might get a few skinny spears, but the bed won’t thrive.
 

3. Stunted or Twisted Growth

Herbicide damage often shows up as twisted, curling, or stunted spears.
 
If your asparagus looks deformed, Preen could be the reason.
 
Stop using it immediately and give your plants time to recover.
 

What to Use Instead of Preen for Asparagus

Don’t worry, you have options.
 
You can control weeds in your asparagus bed without risking your crop.
 
Here are safer alternatives:
 

1. Mulch Heavily

A thick layer of straw, shredded leaves, or wood chips smothers weed seeds.
 
It also keeps moisture in and moderates soil temperature.
 
Just keep mulch a few inches away from the spears to avoid rot.
 

2. Hand Pull Weeds Early

Weeds are easiest to pull when they’re small.
 
Walk your asparagus bed weekly and yank them out before they set seed.
 
It’s more work than spraying Preen, but it won’t kill your asparagus.
 

3. Use a Safe Pre-Emergent

Not all pre-emergents are created equal.
 
Look for products labeled for asparagus, like those containing pendimethalin or metribuzin.
 
Always read the label carefully, because even safe options can harm your plants if misapplied.
 

4. Plant a Cover Crop

In late fall, sow a cover crop like winter rye or crimson clover.
 
It outcompetes weeds and adds organic matter when you till it in.
 
Just don’t let the cover crop go to seed and become a weed itself.
 

So, Will Preen Kill Asparagus?

Preen will kill asparagus, plain and simple.
 
It stops seed germination, damages crowns, and weakens ferns over time.
 
Even if your plants survive the first application, repeated use will ruin your harvest.
 
Instead of Preen, use mulch, hand weeding, or asparagus-safe herbicides.
 
Your asparagus bed will thank you with thick, tender spears for years to come.
 
So skip the Preen, protect your crowns, and enjoy a thriving asparagus patch.