How Deep Should You Plant a Plant? The Mistake That Can Kill an Otherwise Healthy Garden

Your plant might be dying because you buried it alive.

Not deliberately, obviously.

You bought a perfectly healthy plant. Dug a lovely big hole. Added some beautiful soil. Tucked it in nice and deep, gave it a drink and stood back feeling rather pleased with yourself.

Three months later, it's yellow.

Six months later, it's looking miserable.

And now you're standing in the garden wondering whether the nursery sold you a dud.

But the problem might have started the day you planted it.

Because there's something surprisingly important about the depth of a planting hole.

Most plants don't want to be planted deeper than they were growing in their pot.

And while that sounds ridiculously simple, getting it wrong can cause problems that don't become obvious until weeks or months later.

Let's talk about why.

How deep should you plant a plant?

For most ordinary garden shrubs, groundcovers, grasses and strappy-leaved plants, the top of the root ball should finish approximately level with the surrounding soil.

Not buried under another ten centimetres of dirt.

Not sitting in a deep little crater.

And not sticking halfway out of the ground with its roots exposed.

The aim is to position the plant so its roots can grow into the surrounding soil while the stem base or crown remains at the appropriate level.

There are exceptions, of course. Some plants have specific planting requirements, and grafted plants, certain trees and particular bulbs need extra consideration.

But for the majority of plants people buy from an Australian nursery, planting at approximately the same depth as the original root ball is a very good starting point.

And here's the part people get wrong.

The depth of the hole isn't necessarily the depth the plant should sit.

A bigger hole isn't always a better hole

There's a wonderful gardening instinct that says if a little preparation is good, a lot must be better.

So we dig enormous holes.

Deep ones.

Wide ones.

Sometimes holes that look as though we're preparing to install a swimming pool rather than a Westringia.

But while loosening the surrounding soil can be useful, digging unnecessarily deep creates another problem.

The plant can settle.

If you place a root ball on a thick layer of loose backfill, that soil may compress after watering.

And down goes the plant.

What started at the correct height can end up sitting several centimetres below the surrounding ground.

Now water collects around it.

Soil gradually washes towards the stem.

Mulch gets piled on top.

And before long, the plant is considerably deeper than it was ever meant to be.

For most ordinary garden plants, dig the hole wide enough to accommodate the roots and encourage outward growth, but no deeper than necessary to position the root ball correctly.

The bottom should be firm enough to support the plant without excessive settling.

Why is planting too deep bad for plants?

Roots need more than water.

They also need oxygen.

And while roots naturally grow underground, the upper root system and stem base of many plants are adapted to particular conditions.

Burying the stem base or crown too deeply can keep sensitive tissues excessively moist.

In poorly drained soils, this may encourage rot or other problems.

Deep planting can also affect root development and make it harder for some plants to establish properly.

The severity depends on the plant, the soil and the growing conditions.

A plant buried too deeply in free-draining sandy soil may behave differently from one sitting in heavy clay that remains wet for days.

But the general principle remains:

Don't bury parts of the plant that weren't meant to be buried.

What is the crown of a plant?

This is one of those gardening terms worth knowing.

The crown is the region where the roots and above-ground growth meet.

In many clumping plants, it's where the leaves or shoots emerge from the base.

Think about a Lomandra.

Or a Dianella.

Or a Liriope.

The leaves emerge from a basal growing area.

That area is important.

If you bury it deeply under soil or keep it smothered beneath wet mulch, you may create conditions that encourage crown problems in susceptible plants.

This doesn't mean every crown must be exposed above the ground.

It means the plant should be positioned at the appropriate level for its species.

And for most nursery-grown strappy plants, that generally means keeping the original crown at approximately its previous growing level.

How deep should I plant Lomandra?

Lomandra is one of the most widely used plants in Australian landscaping.

And one of the easiest ways to create unnecessary problems is to bury the crown too deeply.

When planting Lomandra tubestock or potted plants, position the root ball so the crown remains at approximately its original growing level.

Backfill around the root ball.

Firm the soil gently.

Water thoroughly.

And avoid piling mulch directly over the crown.

Lomandras are famously useful landscape plants, but they're still living plants with roots and growing points.

They don't need to be buried halfway up their leaves to stop them falling over.

If a plant is unstable, check the planting hole and root ball rather than simply adding another shovel of soil over the top.

How deep should I plant Dianella?

Much the same principle applies.

Dianellas grow from basal crowns and, depending on the species and cultivar, may spread through underground stems or form clumps.

Position the root ball correctly.

Keep the crown at its appropriate level.

Don't bury the base under excessive soil or mulch.

And remember that Dianella varieties differ in their tolerance of wet conditions.

A plant that handles occasional wet soil may still struggle if its crown is continuously buried in saturated material.

How deep should I plant groundcovers?

Groundcovers are particularly easy to plant too deeply because they're small.

You take a little tube out of its pot.

Dig a hole.

Pop it in.

Then backfill enthusiastically until half the foliage has disappeared.

Please don't.

Groundcovers such as Myoporum, Hardenbergia, Westringia and other spreading plants should generally be planted with the top of their root ball approximately level with the surrounding soil.

Keep healthy stems and growing points above ground unless the species has a specific reason to be planted differently.

The fact that a plant eventually spreads across the ground doesn't mean it wants to be buried underneath it.

How deep should I plant tubestock?

This is particularly important if you're planting a large quantity of young plants.

Tubestock is small.

Which is wonderful for affordability and mass planting.

But small root balls are also easy to bury accidentally.

Here's a simple method.

First, water the tube if the mix is dry.

Remove the plant carefully, supporting the root ball rather than pulling hard on the foliage.

Dig a hole that comfortably accommodates the root system.

Position the plant so the top of the root ball is approximately level with the surrounding ground.

Backfill around the roots.

Firm gently to remove large air pockets without compacting the soil excessively.

Water thoroughly to settle the soil around the root ball.

Then check the finished level.

If the root ball has sunk, correct it before walking away.

And if you're planting fifty or a hundred tubes, make a habit of checking the depth as you go.

Because repeating the same little mistake fifty times is still fifty mistakes.

Just considerably more expensive.

Should I cover the root ball with soil?

This is where people can get confused.

You want the roots properly surrounded by soil.

But you generally don't want to bury the stem base under a thick additional layer.

The top of the potting mix should sit approximately level with the surrounding soil, with any exposed roots appropriately covered.

The exact treatment can vary depending on the plant and site.

For trees, identifying the root flare is particularly important.

For ordinary tubestock, aim for a neat transition between the original root ball and the surrounding garden soil.

The goal is to integrate the roots into the ground.

Not build a little mountain over the stem.

What happens if you plant too shallow?

Yes, you can get this wrong in the other direction too.

If the root ball sits too high, roots may become exposed.

The original potting mix may dry out more quickly than the surrounding soil.

The plant may be unstable.

And water may run away from the root ball rather than soaking into it effectively.

This is particularly important with small tubestock because the root volume is initially limited.

You don't want the roots sitting exposed to hot, drying air.

But you also don't want the crown buried.

The aim is the correct level.

Not the deepest possible hole.

What about planting in clay soil?

Clay changes the conversation because drainage becomes important.

If you dig a deep hole in poorly drained clay, fill it with a very different loose potting mix and plant something that hates wet feet, you may inadvertently create a place where water accumulates.

People sometimes call this the bathtub effect.

Water enters the planting hole but moves slowly into the surrounding clay.

The root zone stays wet.

And the plant struggles.

This doesn't mean clay soil is bad.

Plenty of plants grow beautifully in clay.

It means you need to understand the drainage and choose plants accordingly.

In some poorly drained situations, planting into a properly designed raised bed or broad mound may be more appropriate than burying the plant deeply in a hole.

But don't simply perch a root ball on a little pile of soil and assume the drainage problem is solved.

The entire root zone needs to function properly.

Should I put gravel in the bottom of the planting hole?

Usually, no.

This is one of those gardening ideas that sounds logical.

Water drains through gravel, so surely gravel at the bottom of the hole improves drainage?

Unfortunately, soil physics is more complicated.

Adding a coarse layer beneath finer soil doesn't automatically improve drainage and can create an interface that affects how water moves through the root zone.

If you've got a drainage problem, a handful of gravel at the bottom of the planting hole is unlikely to fix it.

You're generally better off understanding the soil, improving the planting area where appropriate and choosing plants suited to the conditions.

The answer to poor drainage isn't always more things in the hole.

Should I add fertiliser underneath the plant?

Not automatically.

And certainly not a random handful of strong fertiliser directly against tender roots.

Newly planted roots can be sensitive to excessive fertiliser salts.

Some Australian native plants also have particular nutrient requirements, including sensitivity to excessive phosphorus in certain groups.

If fertiliser is appropriate, use a suitable product according to its directions and the plant's needs.

But remember:

The first job of a newly planted plant is to establish a healthy root system.

Correct planting depth, suitable moisture and appropriate soil conditions are more important than trying to force instant growth with fertiliser.

Should I add compost or potting mix to the hole?

This depends on the soil and the plant.

A little soil improvement can be useful in some situations.

But filling a narrow planting hole with an entirely different growing medium can create sharp differences between the root ball, the backfill and the surrounding soil.

Roots need to grow out into the garden.

They shouldn't be encouraged to remain in a small pocket of unusually soft, rich material while the surrounding soil remains compacted and unsuitable.

Where soil improvement is needed, improving a broader planting area is often more useful than creating one isolated pocket.

And sometimes the best approach is simply to choose plants suited to the soil you already have.

Should I press the soil down after planting?

Yes, gently.

You want good contact between the root ball and surrounding soil.

Large air pockets can interfere with water movement and root contact.

But there's a difference between firming soil and compacting it.

You don't need to stand on the planting hole and perform a small ceremonial dance.

Use your hands or gentle pressure to settle the backfill.

Then water thoroughly.

Water helps settle soil around the roots and can reveal areas that need a little more backfill.

Should I make a watering basin around the plant?

A shallow watering basin can be useful in some garden situations, particularly during establishment.

It helps direct water towards the root zone.

But be careful not to create a deep permanent depression around plants that dislike prolonged wet conditions.

And don't pile the basin wall against the stem.

In heavy clay or poorly drained areas, trapping water around the crown may be the opposite of what you want.

The goal is to get water into the root zone and allow excess water to move away appropriately.

Not create a miniature dam around every plant.

How much mulch should I put around new plants?

Mulch is enormously useful.

It can reduce evaporation, moderate soil temperature, protect the soil surface and help suppress weeds.

But mulch should generally be kept away from direct contact with sensitive stems and crowns.

Don't bury the base of the plant beneath a thick mound of wet mulch.

And please don't create enormous mulch volcanoes around trees.

The trunk is not supposed to look like it's erupting from Mount Vesuvius.

Spread mulch over the surrounding soil at a suitable depth for the material and conditions.

Leave breathing room around the stem or crown.

Your plant will appreciate the distinction.

Why do trees need special attention?

Trees are particularly vulnerable to certain deep-planting problems.

Many trees have a root flare, the area where the trunk widens as it transitions into the main roots.

This should generally be visible at or near the finished soil surface rather than buried deeply.

A tree planted too deeply can experience problems involving root development, moisture around the trunk and, in some circumstances, girdling roots.

And because trees can take years to show the consequences, the original planting mistake may be long forgotten by the time symptoms appear.

If you're planting a tree, don't assume the top of the nursery potting mix automatically marks the correct depth.

Sometimes trees have already been potted too deeply.

Find the root flare and follow species-appropriate planting guidance.

What about grafted plants?

Grafted plants require extra attention because they contain a graft union where two plant parts have been joined.

Depending on the species and rootstock, burying that graft union can cause problems or change how the plant grows.

Some grafted plants have specific planting-depth requirements.

Always follow the instructions for the particular plant.

This is one of those situations where the general “same depth as the pot” rule may not be enough.

What about bulbs?

Bulbs are another exception.

Different bulbs require different planting depths.

Some are planted relatively shallowly.

Others are planted considerably deeper.

Some have particular requirements around which parts remain exposed.

So don't apply ordinary shrub-planting instructions to every bulb in the garden.

Read the instructions for the actual species.

Why does my plant look fine for months and then suddenly decline?

This is what makes planting-depth problems frustrating.

The consequences aren't always immediate.

A plant may initially survive on the root system it arrived with.

Then as time passes, poor root-zone conditions begin affecting establishment.

The plant might grow slowly.

Leaves may yellow.

New growth may become weak.

The crown may begin to deteriorate.

And by the time the symptoms become obvious, the original planting day feels like ancient history.

But deep planting is only one possible cause.

Similar symptoms can result from overwatering, underwatering, root disease, nutrient problems, unsuitable light and many other issues.

So investigate before deciding you've found the answer.

How can I tell if my plant was planted too deep?

Start by looking at the base.

Has soil accumulated around the stem?

Is the original root ball sitting well below the surrounding soil?

Has mulch buried the crown?

For a tree, can you locate the root flare?

Does the area remain wet for long periods?

Are there signs of crown or stem-base deterioration?

You may need to carefully move loose soil or mulch away to inspect the planting level.

Be gentle.

Don't damage healthy roots while investigating.

And don't assume every plant with yellow leaves is planted too deeply.

We're looking for evidence.

Not a convenient explanation.

Can I fix a plant that's been planted too deep?

Sometimes.

If the plant is otherwise healthy and the problem is simply excess mulch or loose soil around the crown, carefully correcting that level may help.

If the entire root ball is significantly too deep, the appropriate solution depends on the plant's size, establishment and condition.

A recently planted small shrub may be relatively straightforward to lift and reset at the correct depth.

A mature tree is another matter entirely.

And if substantial root or crown damage has already occurred, correcting the level may not reverse the damage.

For valuable established trees, seek qualified arboricultural advice.

Should I plant higher in wet soil?

Sometimes, yes.

In poorly drained conditions, a properly designed raised planting area can help position the root system above persistently saturated soil.

But the important phrase is properly designed.

A broad raised bed or mound that integrates with the surrounding soil is different from leaving a root ball half exposed on top of a tiny pile.

And plant choice remains essential.

If the area is naturally wet, you may be better off using plants that actually enjoy wet conditions.

Rushes and sedges, for example, can be excellent choices for appropriate wet-area planting.

Sometimes the solution isn't forcing a dry-loving shrub into a swamp.

It's planting the swamp.

The five-minute planting check

Before you walk away from a newly planted shrub, groundcover or strappy plant, check five things.

1. Is the root ball at the correct level?

The top should generally be approximately level with the surrounding soil unless the species requires something different.

2. Is the crown or stem base clear?

Don't bury sensitive growing points beneath excess soil or mulch.

3. Is the soil firm but not compacted?

Good contact around the roots without crushing the root zone.

4. Has the plant been watered thoroughly?

Water the root ball and surrounding soil, then check whether the plant has settled.

5. Will the area drain appropriately?

Don't leave a plant that hates wet feet sitting in a hole that remains saturated.

That's it.

Five minutes of checking can prevent months of wondering why the plant isn't growing.

The Plant Hub rule

We spend an extraordinary amount of time choosing the right plant.

We research sunlight.

Compare mature sizes.

Read about soil.

Think about flowers.

Measure spacing.

Then we finally get the plant home and bury it three inches too deep because the hole looked a bit empty.

And that's the bit that gets me.

Because you can choose the perfect plant for the perfect position and still give it a terrible start.

So here's the rule:

The roots belong underground. The crown belongs where the plant is designed to have it.

Don't bury the stem just because you've got leftover soil.

Don't dig a deeper hole because it feels more generous.

And don't assume that a plant sitting in the ground is automatically planted correctly.

Sometimes the difference between a thriving garden and a very expensive collection of disappointments is nothing more exciting than getting the planting depth right.

The plant doesn't need a deeper hole. It needs a better start.