Will Rhododendrons Grow Under Oak Trees?

Having an oak tree in your yard provides a focal point that may be in need of other plants to enhance the garden. Several companion plants support their growth, but will rhododendrons thrive under oak trees? We have researched this, and here's what we've found.

Rhododendrons can be grown under oak trees several feet from the trunk close to the drip line. Since they have shallow roots and the tree has deep ones, there will be no competition for water and nutrients. Most companion plants of oak trees thrive better when grown outside the canopy.

Oak trees have been a symbol of strength, longevity, and endurance. Ironically, they are actually very sensitive to their environment, and the root system is particularly averse to changes in air, nutrient, and water conditions. Before we discuss rhododendrons, it is necessary to understand the nature of oak trees.

How To Plant Around And Under An Oak

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How Sensitive Is The Root System Of An Oak Tree?

Planting under and around oak trees has to be approached with careful selection, placement, and compatibility. The main consideration is to preserve its immediate vicinity and to avoid harming the delicate root system.

An oak tree's roots grow far beyond the canopy or drip line, and the area around the trunk base is the "critical zone" approximately 10 feet in all directions.

Usually, it is best to avoid planting over the critical zone since it could lead to soil compaction and competition for nutrients. However, certain varieties can thrive if selected, positioned, and grown properly.

What Do You Put Around The Base Of An Oak Tree?

Add a layer of organic mulch to act as a growing medium for select plants under and around your oak to avoid having to excavate and risk damaging the roots.

A combination of dried leaves, twigs, tree bark, wood chips, and peat would create a lightweight elevated bed that will not compact the soil and suffocate the roots.

Scatter the mulch evenly around the tree about a foot away from the base of the trunk and extend the layer beyond the drip line. The decomposition process would release organic matter into the soil while maintaining moisture and regulating temperature.

Can Plants Grow Around An Oak Tree?

Plant minimally and choose native or local varieties that naturally grow around oak trees. You need to avoid crowding so there is no competition for soil nutrients and water and adequate ground aeration is maintained.

Select plants with shallow roots and are tolerant to partial shade since the canopy would prevent full sunlight exposure.

It is always an option to simply arrange plants in lightweight containers over a thin layer of pebbles around the tree. Small bushes, shrubs, and other ornamentals in pots would not interfere with the oak's delicate root system. You can change or rotate the arrangements when desired.

How Often To Water Oak?

Once oak trees become established and begin to mature, they require little water and are sensitive to saturation. Choose plants that are tolerant to certain degrees of drought, and if you need to water newly sowed seeds or buds, limit the irrigation to the layer of mulch growth medium.

As much as possible, gradually water the area around the oak tree by hand and avoid using hoses or sprinklers. Hydrate the companion plants only, especially over the critical zone. During the summer, amend the top layer of the compost heap with moistened leaves weekly or when they dry out.

How To Care For Rhododendrons Planted Under Oak Trees

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Rhododendrons are an ideal companion plant for oak trees since they have shallow roots and are able to complement the tree’s growing conditions.

Although they do not have extensive roots, smaller varieties that reach five to six feet in height have shorter root systems as opposed to larger cultivars growing up to 20 feet tall.

Some cultivars are cold hardy, while others are not. It is advisable to know which variety can grow and thrive in the area where you live so that you can provide them with their proper growing environment.

Here are simple ways you can care for rhododendrons planted under oak trees.

Do Rhododendrons Need Plenty Of Water?

Newly-planted rhododendrons require frequent hydration to help establish their roots. Since oak trees are sensitive to moist environments, it is suggested to water them by hand.

Do not install irrigation systems around the perimeter since this can damage the tree considerably.

Once the plant is already established, regular hydration is not necessary anymore. Rhododendrons are fairly drought-tolerant and will only require deep watering once the soil is thoroughly dry.

Where Do Rhododendrons Grow Best?

Make sure that the growing medium is acidic and not too compact. The root system will suffocate and may eventually die when planted in clay soil.

If this is the case, amend the soil by adding organic material, including leaves, compost, and composted manure, to make the medium well-draining and able to support plant life.

Be sure to only amend the portion where the rhododendrons will be planted to not disturb and damage the oak tree’s root system.

How Many Hours Of Sun Can Rhododendrons Tolerate?

The plant should be grown outside the tree’s canopy or drip line to ensure they receive its needed sunlight exposure. They require at least six hours of light per day.

Traditional varieties cannot tolerate direct sunlight, while newer cultivars are able to thrive under such conditions. Be sure to determine which rhododendron species are planted under the oak tree.

What Is The Best Time To Fertilize Rhododendrons?

The plant is not very particular about fertilizing. You are only required to feed rhododendrons during spring or the growing season to help promote flowering. Use plant food specifically formulated for acid-loving growth and vegetation. Organic fertilizers are more advisable for application.

You can use fertilizers with high phosphorus (P) content to encourage the blooms to develop. However, if phosphorus is already present in the soil’s composition and is enough to accommodate the plant’s needs, then it won’t be necessary.

Check out Miracle-Gro Water Soluble Acid-Loving Plant Food on Amazon.

When Should Rhododendrons Be Pruned?

Rhododendrons are sensitive to pruning. Only trim the flowers when they begin to wilt. This way, the roots will concentrate on storing nutrients for next year’s blooming season instead of producing seeds.

You can remove dead and damaged branches at any time of the year.

Cold Hardy Rhododendrons

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Tropical Rhododendrons

What Grows Best Under Oak Tree?

old oak tree english meadow on the middle of the mountain field, Will Rhododendrons Grow Under Oak Trees?

One way to possibly determine which plants grow best under oak trees is through their natural habitat. Any forms of vegetation you can see thriving around and underneath the tree’s canopy are viable options you can choose.

Aside from rhododendrons, there are several other companion plants for oak trees since they do not interfere with the root system and affect their growth.

Grape hyacinth, California iris, coal bells, shooting star perennials, ferns, and hostas to name a few are plants best grown under oaks.

Grape Hyacinth

Grape hyacinth is a perennial that produces purple flowers. They can be planted as border plants under the tree’s canopy since they thrive best in partial shade. They are not particular about their hydration needs. Keep the soil thoroughly dry in between watering.

Get grapy hyacinth bulbs on Amazon.

Coral Bells

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Coral bells produce pink, red, and white clusters of bell-shaped flowers that attract beneficial insects, hummingbirds, and butterflies. They reach a mature height of only 12 to 36 inches (1 to 3 feet).

Get coral bell seeds on Amazon.

Shooting Star Perennials

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Shooting star perennials should be grown a few feet away from the tree’s drip line since they require slightly moist environments. Although this is the case, frequent hydration is not necessary – an inch of watering once a week is beneficial.

Get shooting star seeds on Amazon.


Ferns can be grown closer or at the tree’s trunk because they do not compete for nutrients found underneath the ground. Their roots gather nutrients from airborne dust. The plant’s growing conditions are similar to an oak tree in terms of watering and soil requirements.


Hostas are perennial plants best grown underneath old oak trees since most varieties prefer shady environments. They have a shallow root system and are drought-tolerant. They only require additional watering during periods of extreme heat and long dry spells.

In Closing

old oak tree English meadow on the middle of the mountain field

Rhododendrons as well as a few other select plants can be grown under and around oak trees. The article has demonstrated that it is the environment and conditions surrounding the tree that is the critical factor in the process. We hope the article helped you in this regard.

You might also find these topics informative:

How Far From House Should Oak Tree Be Planted?

How Much Water Does An Oak Tree Need?

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