In many cases, that's true.

As the days become cooler, the soil is often still warm from summer, giving roots the opportunity to establish before the burst of growth that comes with spring. For many trees and shrubs, this combination of warm soil, cooler air and more reliable rainfall creates excellent planting conditions.

But like most gardening advice, there isn't a one-size-fits-all answer.

A tree planted into waterlogged clay or an exposed, windswept corner won't thrive simply because it went into the ground in September. The success of any planting depends just as much on the conditions in your garden as it does on the season.

If you're considering a larger purchase, understanding why autumn is usually recommended—and when it might be better to wait—can help you make a decision you'll still be happy with years from now.

Why autumn planting works so well

Plants don't stop growing the moment summer ends.

While many deciduous trees and shrubs begin to lose their leaves and enter dormancy above ground, their roots can continue growing as long as soil conditions remain suitable. Instead of using energy to produce fresh leaves and shoots, the plant focuses on establishing a stronger root system.

That early root growth gives plants a valuable head start before spring arrives.

By the time warmer weather returns, an autumn-planted tree or shrub has often already begun settling into its new home, making it better prepared to support fresh growth.

For gardeners, autumn planting can also be easier to manage.

Lower temperatures mean plants lose less moisture through their leaves, while autumn rainfall often reduces how frequently you'll need to water compared with planting during late spring or summer. Newly planted trees still need checking—especially during dry spells—but the conditions are generally more forgiving.

Why it's especially worthwhile for larger trees and shrubs

Buying a tree or mature shrub is an investment in the future of your garden.

Whether you're creating privacy, adding structure or planting a feature tree, you want it to establish successfully from the beginning.

Larger plants naturally have a bigger root system to support. Giving those roots several months to settle before the demands of spring and summer can make establishment easier than planting into warm, drying conditions later in the year.

That doesn't mean bigger plants are maintenance free.

Every newly planted tree or shrub needs regular attention during its first growing season. Water thoroughly after planting, keep an eye on soil moisture during dry weather and apply mulch where appropriate to help conserve moisture and reduce weed competition.

Autumn isn't always the best time

Here's the part that's often left out.

Autumn is usually the best time to plant—not always.

If your garden suffers from standing water throughout winter or the planting area remains saturated after rain, waiting until conditions improve may be the wiser choice.

Roots need oxygen as much as they need water. In permanently waterlogged soil, they struggle to establish and may eventually decline.

Likewise, frozen ground isn't suitable for planting, and very exposed sites may present additional challenges for less hardy plants during their first winter.

The calendar alone doesn't determine whether it's the right time to plant. Your garden does.

Check your drainage before you buy

One of the most important things you can do before buying a tree or shrub is to understand how well your soil drains.

After heavy rain, ask yourself:

If the planting hole fills with water and stays that way, simply digging a larger hole won't necessarily solve the problem. In some situations, it can create a basin that holds water around the roots rather than allowing it to drain away.

Where winter wet is a recurring issue, improving the wider soil structure, planting slightly proud where appropriate, or choosing plants better suited to damp conditions is often a more effective long-term solution.

Don't forget about wind and exposure

Sunlight isn't the only thing that determines whether a tree or shrub will thrive.

Exposure is just as important.

Many Dublin gardens experience varying degrees of wind, from sheltered suburban gardens to more exposed sites where strong winds can make establishment difficult.

Young trees can rock backwards and forwards before their roots have properly anchored, while evergreen shrubs may lose moisture from their leaves during cold, drying winter winds.

If your garden is particularly exposed, you may need to:

A plant that performs beautifully in a sheltered garden may struggle in an exposed one, even if both are planted on the same day.

Should you wait until spring?

Sometimes, yes.

If your soil is frozen, heavily waterlogged or your planting area isn't properly prepared, waiting until spring is often the better decision.

Likewise, if you're unsure whether the location is suitable, it's worth taking a little more time rather than rushing because autumn is considered the traditional planting season.

Successful gardening isn't about following rules blindly.

It's about matching the right plant to the right place.

Before investing in a tree or shrub

Before making your final decision, it's worth considering a few practical questions.

Answering these questions now can prevent disappointment later.

A tree that outgrows its space or struggles in unsuitable conditions is far more frustrating than waiting a few weeks for better planting conditions.

The bottom line

For many gardens, autumn really is one of the best times to plant trees and shrubs.

Warm soil encourages root growth, cooler temperatures reduce stress and more reliable rainfall often makes establishment easier than planting during the height of summer.

But successful planting isn't just about timing.

Good drainage, suitable exposure and choosing the right plant for your particular garden will always have a greater impact than simply planting in the "right" month.