Will Arborvitae Grow Near Black Walnut Trees

Arborvitae will not grow well near black walnut trees.
 
That’s the short answer, and it’s rooted in a fascinating chemical process called allelopathy.
 
Black walnut trees produce a substance called juglone, which is toxic to many plants, and arborvitae is one of the plants that can struggle when planted too close.
 
If you’ve been wondering whether arborvitae will grow near black walnut trees, this post will walk you through why it’s a risky pairing, the signs of juglone damage, and what you can do if you already have both in your yard.
 
Let’s dig into the details so you can make an informed decision for your landscape.
 

Why Arborvitae Won’t Grow Near Black Walnut Trees

Arborvitae will struggle to grow near black walnut trees because of juglone, a natural chemical the tree releases into the soil.
 
Juglone is a defense mechanism that helps black walnut trees eliminate competition from other plants.
 
For arborvitae, this chemical can cause stunted growth, yellowing foliage, and even death over time.
 
Here’s why arborvitae is particularly vulnerable.
 

1. Juglone Sensitivity in Arborvitae

Arborvitae, also known as Thuja, is highly sensitive to juglone.
 
Unlike some juglone-tolerant plants like yews or junipers, arborvitae doesn’t have the same ability to detoxify or tolerate this chemical.
 
When arborvitae roots come into contact with juglone in the soil, they absorb it, and the chemical interferes with their metabolic processes.
 
This is why arborvitae planted near black walnut trees often fail to thrive.
 

2. How Black Walnut Trees Release Juglone

Black walnut trees release juglone from their roots, leaves, bark, and even their nut hulls.
 
The highest concentration is found in the roots, which can extend far beyond the tree’s canopy.
 
In fact, arborvitae planted anywhere within the root zone of a black walnut tree could be affected.
 
That zone can extend up to 50 feet or more from the trunk, depending on the tree’s size.
 

3. Soil and Environmental Factors

Juglone is more persistent in certain soil conditions.
 
For example, in poorly drained or compacted soil, juglone breaks down more slowly, which means it lingers longer and affects arborvitae more severely.
 
On the flip side, well-drained, aerated soil with plenty of organic matter can help dilute and break down juglone faster.
 
But even then, arborvitae growing near black walnut trees will likely still suffer.
 

Signs Arborvitae Is Suffering Near Black Walnut

If you’ve already planted arborvitae near a black walnut tree, you’ll want to watch for telltale signs of juglone damage.
 
These signs can take weeks or even months to appear, depending on the size of the tree and the concentration of juglone in the soil.
 
Here’s what to look for.
 

1. Yellowing and Browning Foliage

One of the first signs arborvitae is struggling near black walnut is yellowing foliage.
 
The needles may turn pale green, then yellow, and eventually brown.
 
This often starts at the tips of the branches and works its way inward.
 

2. Stunted Growth

If your arborvitae isn’t growing as quickly as it should, juglone could be the culprit.
 
New growth may be sparse, and the plant may fail to put on the usual amount of height and width each year.
 

3. Wilting and Dieback

In severe cases, arborvitae will wilt even when soil moisture is adequate.
 
Branches may die back, and the plant may eventually collapse.
 
By the time these symptoms appear, it’s often too late to save the arborvitae.
 

Can You Grow Arborvitae Near Black Walnut Trees With Protection?

You might be able to grow arborvitae near black walnut trees if you take protective measures.
 
But it’s important to understand that these solutions aren’t guaranteed to work, especially if the black walnut tree is large and established.
 

1. Physical Barriers

One option is to install a physical barrier between the arborvitae and the black walnut roots.
 
You can dig a trench and line it with a heavy-duty root barrier or a raised bed with an impermeable bottom.
 
This can help block juglone from reaching the arborvitae roots.
 

2. Improved Soil Conditions

Amending the soil with organic matter can help break down juglone.
 
You can mix in compost, aged manure, or other organic materials to improve drainage and microbial activity.
 
Healthy soil microbes can help neutralize juglone over time.
 

3. Regular Watering and Mulching

Keeping arborvitae well-watered and mulched can reduce stress and help them cope with juglone exposure.
 
But be careful not to overwater, as soggy soil can make the problem worse.
 
Apply a layer of mulch around the base of the arborvitae, but keep it a few inches away from the trunk.
 

So, Will Arborvitae Grow Near Black Walnut Trees?

Arborvitae will not grow well near black walnut trees because of juglone toxicity.
 
While some plants can tolerate juglone, arborvitae is not one of them.
 
If you already have arborvitae near a black walnut tree, watch for signs of decline and take action quickly.
 
But in most cases, the best solution is to plant arborvitae far away from black walnut trees to give them the best chance to thrive.
 
If you’re planning your landscape, keep this in mind so you can avoid the frustration of watching your arborvitae struggle.