Adding a garden arbor to your front or backyard is a great way to add charm and character to your outdoor space. However, placing an arbor in an existing garden requires extra care because you want to avoid harming established root systems or injuring your plants. 

You can preserve the health of your garden by taking measurements ahead of time and estimating the size of your plant’s root balls. This precaution will allow you to install your arbor without disturbing root systems. 

The first measurement you should take is the size of your arbor’s post holes. 

Post Hole Size Requirements

The appropriate post-hole size depends on your arbor’s design. Lightweight soil-mounted arbors only require holes 12 inches in diameter. Poles with poured concrete reinforcements provide more stability but require holes that are  2–3 feet deep and 1–2 feet wide.

Concrete reinforcements also require you to be more careful while digging, as creating larger holes could lead to more root disturbance. 

Garden arbor over path in yard

Estimating Plant Root Spread

To avoid damaging existing root systems, you need to estimate your plants’ root spread. You can use one of two methods to do so.

As a general rule, roots extend at least as wide as a plant’s foliage diameter. Measure the widest point of a plant to estimate the minimum spread of the roots. For example, a 3-foot wide rose bush likely has roots extending 3 feet from the main stem. 

You can estimate how far a shrub or tree’s roots extend outwards by using the size of the trunk. According to the Generic Root Ball Size Guide from the Tennessee Arboretum, the formula for estimating root ball size is as follows : 

  • 1⁄2 to 1-inch trunks: Multiply the trunk’s diameter by eighteen. Thus, a 1-inch trunk likely has roots reaching 18 inches. 
  • 1 to 1 1⁄2-inch trunks: Multiply the trunk’s diameter by sixteen.

Using the above methods to estimate plant root spread can save you time and unnecessary digging. 

Planning Pole Placement

You can now create a visual plan for your arbor’s location using these measurements. Start by indicating the estimated dimensions of the root ball sizes on your blueprint. Then mark your proposed post-hole locations so they are well away from these areas. Including a buffer zone of at least a few inches around each post hole is a good idea. 

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If your arbor includes a swing, you should place the entire structure several feet away from existing plants. This is because load shifts can occur when using an arbor swing, which in turn can cause soil disturbances and unintentional uprooting.

Building your arbor swing well away from your plants’ root systems can prevent this issue.

Installing the Arbor

When your blueprint is complete, you can begin building your arbor. Begin by digging your post holes. It is best to use hand tools, like a trowel or a shovel, for this task. Avoid tearing or cutting exposed roots that you find. If you do slice a root, prune it cleanly to encourage new growth. 

Insert the posts into the post holes and backfill with concrete or existing soil. You can then firmly tamp the solid down around your post placements. This action will stabilize the posts and provide a secure foundation for the overhead arbor. 

After installation, water your plants, monitor them for stress, and prune them as necessary. 

FAQs About Installing a Garden Arbor Near Existing Plants

How close can garden arbor posts be to plants?

You should plan to place your post holes at least as far from stems and trunks as the estimated root spread. Leave a larger buffer of a few extra feet if possible.

What precautions should be taken when digging near roots?

It is best to use hand tools and dig carefully to cause as little disturbance as possible. You also want to avoid tearing or slicing roots. If you do damage a root, be sure to prune it cleanly. Keep in mind that the majority of plant roots are located just below the surface of the soil. 

Should I use new soil to backfill my arbor’s post holes?

It is best to backfill with existing soil. Adding fertilizer or new dirt could change your yard’s soil composition and unnecessarily stress your plants. 

How can I help plants recover after installing my arbor?

You can keep your plants healthy by watering them after you finish building your arbor. You can also prune any roots damaged during the building process to encourage them to regrow. Finally, you should monitor your plants’ health for the remainder of the growing season. 

Editorial Contributors
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Sabrina Lopez


Sabrina Lopez is a senior editor for Today’s Homeowner with over 7 years of writing and editing experience in digital media. She has reviewed content across categories that matter to homeowners, including HVAC services, home renovations, lawn and garden care, products for the home, and insurance services. When she’s not reviewing articles to make sure they are helpful, accessible, and engaging for homeowners like herself, Sabrina enjoys spending time with her family and their two parrots.

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