Did you know that many newly planted trees don’t survive because they are planted incorrectly? It may not seem too important, but it’s surprising how picky young trees can be about how and where they are planted.
One of the most common issues with tree planting that we come across is trees being planted too deep. In fact, we wrote an entire blog post on how deep you should plant a tree.
But, when you’re planting a tree, you not only need to focus on the depth but also the width of the planting hole.
In this article, we go over everything you need to know to choose the best planting hole size for a young tree, including:
- how wide the hole should be (and why),
- what happens to a tree if the planting hole is not wide enough,
- what tree roots need and what they provide,
- and more!
What to do Before You Plant
Before you start digging, double check that you are planting the right tree in the right place. Pay attention to the following:
- how much sunlight the area receives,
- what the fully grown size of the tree will be (including the width and how much room the tree roots need to grow!),
- if the area is near a walkway,
- if the tree will have thorns or fruit, and
- whether the tree is native to our area.
We recommend moistening the area where you want to plant a few days before digging. This will make digging in tough garden soil slightly easier.
Reminder: Don’t Dig Too Deep!
Planting a tree too deeply can cause serious health issues for your tree. Ensure that any planting soil is removed from the root flare (it can often become buried at nurseries) and dig a hole that is no deeper than the length from the bottom of the root ball to the root flare.
If you place the tree in the planting hole and the top of the root flare is below ground level, you have dug too deep. Add some of the soil you removed back into the hole and make sure it’s firmly tamped down (but don’t stomp on it!) before placing the tree into the planting hole.
How wide should the planting hole be?
The planting hole width should generally be 2 to 3 times as wide as the hole is deep (and remember that depth should equal the height of the root ball).
For example, if the root ball is 1 foot tall, your planting hole should be 1 foot deep and 2 to 3 feet wide at the top.
There’s no need to dig the hole 1 foot deep AND 2 to 3 feet wide. Instead, once you’ve dug a hole that’s 1 foot deep and roughly 1 foot wide, you can start to taper the sides upward as you widen the hole. The goal is to create a bowl-shaped hole that’s flat on the bottom.
Unlike the depth of the planting hole, it’s okay if you dig a hole that’s wider than it needs to be. We cover more about why this is the case later in this article.
The worst thing you can do is to dig a hole the same size (depth and width) as the container the tree comes in. We get it – it can be tough to dig a large hole and it probably seems that it won’t do much harm to cut a few corners when planting. But doing this is just asking for problems that will often cost you far more money and effort than planting the tree properly.
What happens if the planting hole isn’t wide enough?
If the planting hole isn’t wide enough, your tree won’t grow properly. It will likely develop root problems that compromise its health, stability, and long-term survival.
Most newly planted trees were previously in nursery containers. Often, we see that the roots have started to grow in circles inside the pot. If planted in a hole that is not much wider than the space they had in the nursery container, the roots will simply continue to grow in a circle.
Circling roots can become girdled roots as the tree grows, causing the roots to essentially choke the tree. Girdled roots are roots that are so close to the tree’s trunk that they restrict the tree’s growth and ability to take up water and nutrients. You may notice girdled roots near the base of your tree, or they may be underground and not as noticeable.
While girdled roots may not become an issue for several years, they will greatly reduce the lifespan of your tree.
Roots That Don’t Anchor Your Tree
Roots that are confined to a small area also mean that your tree will be less firmly anchored in the soil. This can become a problem during high winds or monsoons when trees are more easily uprooted. Without an expansive root system, your tree will be more likely to fall over. This not only kills the tree but can cause damage or injury to anything in the drop zone of the tree.
It’s All About the Roots!
Despite popular belief (and many incorrect drawings), tree roots do not grow down into the soil and create a mirror image of the tree above ground. Rather, they spread out like a frisbee and are often no more than 8 to 12 inches below the surface at any point (they sometimes grow above ground as well).
As you can imagine, a narrow (and deep) planting hole will make it difficult for roots to spread out. This limits the ability of tree roots to support the tree.
Small Planting Hole = Less Water
Tree roots carry water to the rest of the tree. Most rainwater is found closer to the soil surface, especially in the desert. While some trees and cacti such as the saguaro also have a taproot that helps them to survive long periods of drought, desert trees are more likely to depend on their wide-spreading roots that gather water from the surrounding area closer to the surface.
This is also why it is vital to provide water to a newly planted tree for the first several years – the roots have not yet branched out far enough to receive enough water just from our native rainfall.
Note: Mesquite trees also have a taproot. You can learn more about mesquites and their (sometimes invasive) roots in this article: The Pros and Cons of Mesquite Trees.
Small Planting Hole = Less Oxygen
Roots also provide oxygen for the tree. The air pockets in soil are important not only for roots to grow and move, but for the tree to receive oxygen. Roots not only carry water to the tree, but also oxygen and nutrients found in the soil. There is more oxygen found in soil near the surface than deeper in the ground.
Small Planting Hole = Fewer Nutrients
Lastly, tree roots absorb vital nutrients that are found in the top layers of soil. Again, looking at nature, there are always decaying plants and animals found throughout the desert, leaving valuable nutrients behind. Leaves, branches, decaying trees and cacti, fungi, flower petals and more are being broken down and added to the soil, increasing the nutrients available for growing trees and plants.
These nutrients are not as common in urban and suburban environments, which is why we encourage the use of organic wood mulch whenever possible. You may also consider fertilizing your trees after a few years if they are struggling.
What if I can’t dig a wide enough hole?
The Phoenix and Anthem areas have soil that is sometimes filled with caliche, or soil that is compacted and has become rock-hard. We’ve seen people use a jackhammer to dig a planting hole!
Not only does caliche make it very difficult to dig a planting hole, it can also make it difficult for tree roots to grow outward or downward to firmly anchor the tree and access moisture deeper in the soil. Conversely, caliche can also “drown” a tree by preventing water from soaking deeper into the soil; instead, it stays in the soil around the tree’s roots.
How do you know if there’s caliche where you want to plant your tree? Once your planting hole is dug, fill the hole with water and wait for it to drain. If it has not drained within 24 hours, you may be dealing with caliche in the soil.
If there is caliche, your best bet is to choose another location in which to plant your tree. But if your only option is to plant where there is caliche, you will have to make some adjustments to your planting hole.
Not sure what to do? Check these adjustments to make when there is caliche where you want to plant a tree. Note that these adjustments don’t include digging a narrower planting hole!
What else can impede a new tree’s root growth?
Not removing nursery containers
Trees may be transported in a variety of containers. Most come in a five-gallon bucket from a nursery when they are still quite small, and may have a single stake next to the tree trunk. Others may have a wire basket or burlap around the root ball to protect it.
While these items are useful for growing at a nursery or for transporting the tree, they absolutely must be removed before planting, including the nursery stake. We have seen plants that were planted with the wire basket or burlap still wrapped around the root ball. The reason we have seen it is because these trees eventually fall over, with most of their roots still stuck inside the container that was only meant to be temporary.
The nursery stake is not appropriate for “staking” a young tree so get rid of that too.
Watering the trunk
We’ve written often about the importance of watering young trees, but how you water them is also important. If you’re watering the trunk, you are encouraging the roots to stay near the trunk. Instead, you want to encourage them to branch out. This is why you should always water the “drip line” of a tree, or where the water would naturally drip off of the edge of the tree’s canopy.
If you have an irrigation system set up near your tree, make sure it is not too close to the trunk of the tree. We don’t recommend watering your tree through irrigation unless the tree is on a separate zone than landscape plants or lawn. Trees need slow and deep watering, not the frequent and light watering that most other plants receive.
Planting too close to a structure, sidewalk, or roadway
Compacted soil is even more compacted when it is covered by a structure or walkway. Planting a tree next to a driveway, sidewalk, or building will make it difficult for tree roots to expand.
Additionally, if the roots do grow beneath a sidewalk or driveway, they won’t receive enough oxygen. This may result in tree roots growing upwards, breaking the sidewalk or driveway and causing more problems in the long run.
No Mycorrhizae in the Soil
Compacted and nutritionally depleted soil can reduce the chances of this friendly fungus in your soil. While property owners often think of fungi as a bad thing, mycorrhizae act as an extension of your tree’s roots, bringing more nutrients and water to the roots and helping plants and trees communicate through a fascinating underground web.
Tree roots are the lifeblood of a tree. They bring water, nutrients, and oxygen to the rest of the tree and allow it to grow and thrive. While roots keep growing as long as a tree is alive, giving them a good start when a tree is planted is the first step in ensuring you have a healthy tree that will provide shade and other benefits for a long time to come.
The next time you add a tree to your property, remember to keep the planting hole the right depth and 2 to 3 times wider (or more) than the size of the root ball.
If you have any questions about tree planting or a tree’s root system, contact Titan Tree Care to schedule a tree consultation.