There seems to be an assumption amongst some gardeners that hydrangeas can cause issues with tree roots.
This might account for the fact a question I see asked regularly is will hydrangeas grow under oak trees?
In fact not just oak trees, but pine trees, cedar trees and many others.
So let’s get to the root of the problem (pun intended).
Will Hydrangeas Grow Under Oak Trees?
As long as you don’t plant your hydrangea too close to the base of an oak tree, it will grow just fine. When choosing a spot to plant make sure there aren’t lots of tree roots around competing for moisture and nutrients and make sure it will receive at least some sunlight. Hydrangeas will also grow well under pine, cedar and redwood trees, but will struggle under walnut and gum trees.
Yes, As Long As You Plant Them Sensibly
Hydrangeas and oak trees should be able to exist and flourish together as long as you take a little care when planting.
When you choose a spot to plant, you want to make sure there are not lots of tree roots around.
If you plant hydrangeas too close to an oak tree, the tree will outcompete the hydrangeas for water and your hydrangeas will wilt, a lot.
They both have a shallow root system and don’t need a lot of groundwater, so in that respect they make good companions.
However, you still need to make sure your hydrangeas get some sun.
Hydrangeas bloom best with a few hours of sun. Ideally, this will be in the morning when the sun isn’t yet at its strongest.
There are two things you want to avoid:
- Your hydrangea being in the sun all day. Planting under the canopy of a tree this is unlikely.
- Your hydrangea being in dense shade all day. Planting under the canopy of a tree, this is more likely.
So planting it too close to the tree will deprive it of the sun it needs and also mean it will be fighting with the oak tree for moisture etc.
Certain types of hydrangeas can withstand more shade than others, varieties like oakleaf and climbing hydrangeas being examples.
If you have any concerns, test the water with a few shrubs at first and see how they do.
But as long as you plant sensibly, hydrangeas should do just fine under oak trees.
But what about other trees?
Let’s take a look…
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Will Hydrangeas Grow Under Pine Trees?
Growing hydrangeas under a pine tree is trickier but definitely possible.
Pine trees have an extensive and shallow root system, and digging through the surface roots to plant your hydrangea can be difficult.
One thing that will benefit hydrangeas is the fact the soil pH under pine trees is acidic.
That is the type of soil both hydrangeas and pine trees prefer. Also, decomposing pine needles that fall from the tree and decompose are slightly acidic.
But pine trees suck a lot of moisture from the soil, which could leave any hydrangeas you plant around a pine tree struggling.
You would need to add some organic material to the soil to help it retain moisture that the hydrangea can take up to account for the lack of water in the soil due to the thirsty pine tree.
On top of that, you will probably need to water the hydrangeas regularly during the growing season every two or three days.
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Also, as we touched on when discussing if hydrangeas will grow under oak trees, hydrangeas do like some sun.
Certain types of pine trees can have very dense canopies which will deprive the plant of both sun and rain.
Hydrangeas will therefore fare much better under a white pine, which has a loose canopy, than a stone pine, which has a denser canopy.
So as long as you meet a few conditions hydrangeas should grow well under a pine tree.
Make sure the canopy isn’t too dense, make sure you don’t plant too close to the trunk, amend the soil with organic matter and mulch and water regularly.
Do all of that and you should get some lovely blooms from your hydrangeas.
Will Hydrangeas Grow Under Cedar Trees?
The good news here is that both hydrangeas and cedar trees have a lot of the same growth requirements.
Both like morning sun and afternoon shade, both like moist, rich, well-draining soil and both like soil that is slightly acidic.
Both will also benefit from top dressing with good quality compost and a couple of inches of mulch to help with moisture retention.
Again a few variables are at play here, ie where you live, what variety of hydrangea you want to plant, but generally hydrangeas and cedar trees are compatible.
You just need to remember to make sure your hydrangea gets the sun it needs and is regularly watered and it should thrive.
Will Hydrangeas Grow Under Walnut Trees?
All species of walnut tree produce a substance called hydrojuglone.
When this substance is exposed to air or soil it gets oxidized and turns into juglone. Juglone is harmful to many plants as it starves them of water and oxygen.
It is the walnut tree’s way of defending its territory.
Many plants are tolerant of juglone and, as a result, can’t be planted under a walnut tree.
But are hydrangeas juglone tolerant?
The answer to this varies.
There are very few studies on the impact of juglone on particular plant species, and as a result it can be difficult to say with 100% certainty whether hydrangeas will grow well under a walnut tree.
Again there are variables that come into play, including the species of hydrangea and the level of toxicity of the walnut tree.
Nonetheless, during my research, I did find a number of people saying there were growing hydrangeas under walnut trees successfully.
If you are going to try, then remember to plant in a spot that gets some morning sun and then shade later in the day, and follow all the other guidelines for growing healthy hydrangeas, ie making sure the soil remains moist, etc.
I’d love to hear how you get on in the comments section.
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Will Hydrangeas Grow Under Redwood Trees?
The one issue in general with redwood trees is that they are usually so dense very little rainfall gets through their canopies.
As with pine trees, the key to successfully growing hydrangeas under redwood trees is ensuring they get the moisture they need.
Place mulch around the soil and water regularly.
Make sure they aren’t planted too deep in the shade of the tree.
Keep a close eye on them, but providing they get sufficient amounts of moisture and nutrients they should be fine.
Will Hydrangeas Grow Under Gum Trees?
Like walnut trees, gum trees or eucalyptus trees as they are more commonly known, are allelopathic.
This means they produce compounds that can stop any plants nearby from growing. This compound is in the leaves of gum trees.
On top of that large amounts of biomass build up when eucalyptus leaves and bark are shed, which limits the light and oxygen surrounding plants can receive.
These two factors make it even more difficult to grow hydrangeas under gum trees and the list of plants that can grow under Gum trees is relatively limited.
Hydrangeas will grow well under most trees, namely oak trees, pine trees, redwood trees and cedar trees.
When it comes to walnut trees and gum trees, like many plants, they are much less likely to thrive.
Hydrangeas will not cause issues to trees, it is more likely to be the other way around.
So if you want to plant your hydrangea under an oak tree (or any of the other trees mentioned above) make sure it is planted sufficiently far enough from the base of the tree to:
- Not be competing with it for water and other nutrients.
- Not be in full shade all of the time.
Remember those two principles and makes sure there is plenty of moisture in the soil at all times and they will grow just fine.