Mimosa Tree

TREES > MIMOSA

The name ‘Mimosa Tree’ is the common name for two non-native tree species – Albizia julibrissin and Acacia dealbata, even though neither belong to the Mimosiae genus.

Online and in books, you will frequently hear horror stories about these plants, which can be hugely invasive in some areas.

You may also read, however, about how they can help in sustainable design and ecosystem restoration…

However, the pros and cons of these trees very much depend on where they are grown.

Overview

Botanical Names	Albizia julibrissin / Acacia dealbata
Common Name(s)	Mimosa Tree, Pink Silk Tree, Silver Wattle, Blue Wattle
Plant Type	Tree
Native Area	E. Transcaucasus to Japan and South East Australia
Hardiness Rating	H3-H4
Foliage	Deciduous / evergreen
Flowers	Yellow / pink-white blooms
When To Sow	April, May, June / September, October
Flowering Months	March to April or July to August
When To Prune	May / October

While Mimosa trees can certainly bring serious issues for local ecosystems where they become invasive, this is typically not an issue in UK gardens, where these trees are much harder to grow.

Still, though they can bring certain benefits, there are a number of reasons why they may not be the best choices for many UK gardens (which have nothing to do with their potentially invasive nature).

Read on to learn a little more about the pros and cons of both of these mimosa trees:

Pink Silk Tree

Botanical Name: Albizia julibrissin

Albizia julibrissin, also known as ‘Pink Silk Tree’ and commonly referred to as ‘Mimosa’ in the US, certainly is an attractive flowering tree.

It is a deciduous tree with rose-pink fluffy flower heads which open in the summer months, and features interesting and exotic-looking bipinnate leaves.

This plant is native to Ethiopia, Iran to Japan and China, though it has extensively naturalised elsewhere.

Pros

Nitrogen Fixation

One of the main reasons why this can be a very useful plant in many regions is that. because it belongs to the Pea family Fabaceae, it is a nitrogen-fixing plant, meaning it deposits nitrogen in the soil it grows.

As it can cope with a huge range of different soil and climatic conditions, this can make it a useful pioneer plant, which can be used to reclaim degraded landscapes and as a key species in forest gardens and agroforestry schemes.

Not Typically Invasive (In The UK)

This tree is H4 hardy and can be grown in some UK gardens with sufficient sun, warmth and shelter. However, in the climate of the British Isles, it rarely sets seed.

This means that it is not as problematic as an invasive as it can be in parts of the US, and other areas.

In southern, sheltered gardens, this can be an interesting option to consider – the tree is a suitable size for small gardens so can work well in some sheltered urban plots, and it is ideal for training against a sunny south-facing wall, or for container growing.

Honey Fungus Resistance

One other interesting plus point of this tree is that it is notably rarely affected by honey fungus.

So for gardeners who have had issues with this fungal disease, it could be a good choice.

Cons

It really only succeeds in the very mildest parts of the British Isles without protection, or being brought under cover during the winter months.

Hardiness

If you do not have a particularly warm, sunny and sheltered garden then this may not be the easiest plant to grow and lower maintenance alternatives may be a better choice.

Remember, this is a non-native plant and native options can often be better for your garden.

Alternating spells of mild and cold weather can damage the top growth, and though these can and do often regrow from the ground when damaged by frost, the damage can be unsightly.

“Newer growth over the summer can become damaged by winter frost, but these stems can be pruned out in the late spring to improve the appearance of the plant which produces the fern-like foliage from the early summer,” says Master Horticulturist Roy Nicol.

It is also worth noting that though it is notably resistant to honey fungus, it can be affected by other diseases, such as verticillium wilt.

Tendency To Spread

Though the plant will not usually set seed in the UK, it can still spread.

Plants often produce suckers and send up saplings, sometimes quite far from the parent tree.

The strong root system can make these difficult to remove.

The strong root system can crack concrete pavers or driveways, damaging the infrastructure in your garden.

Though of course, this is not an issue when grown in containers.

Mess below the tree is also a concern to some – flowers dropping off the tree can be a problem for some very neat and tidy gardeners.

Silver Wattle

Botanical Name: Acacia dealbata

Acacia dealbata, also known as mimosa, silver wattle or blue wattle, is also sometimes grown in the UK.

It is native to Tasmania and parts of mainland Australia.

Pros

Nitrogen Fixing

This plant is H3 hardy, but where it can be grown, this is another useful nitrogen-fixing plant.

Remember, nitrogen-fixing plants have symbiotic relationships with bacteria in their root nodules which can turn nitrogen from the air into nitrogen in the soil.

Some of the nitrogen is used by the plant itself, but some may also be taken up by other plants in the vicinity.

Drought Tolerant

Like the above, this is a good pioneer plant for some climate zones.

It is drought-tolerant and may be a good choice for lower rainfall areas.

Preventing Soil Erosion

This tree also has an extensive root system, which helps prevent soil erosion.

So it can be a useful addition in areas with poor, light soils which can easily be eroded.

Like the above, this mimosa is also a good choice for small spaces, and it can also be grown in containers, or trained against sunny, south-facing walls.

The flowers of silver wattle are fragrant, so can be pleasant when located close to windows or seating areas, and the flowers are edible too.

Cons

Hardiness & Soil Requirements

Like silk trees, silver wattle can only be grown without winter protection in milder parts of the British Isles, and requires a sheltered position.

So again, it is not the most low-maintenance choice and you may find many of the same benefits with other lower-maintenance trees and plants.

It is also worth noting that while Acacia dealbata can work well in many different conditions, it is not suitable for heavy clay or limey soils.

Remember, as an H3 hardy plant, this tree must usually be moved under cover in winter unless you live in a particularly mild and warm part of the British Isles.

They really do need hot, sunny summers to mature and flower successfully.

Invasiveness

Mature specimens sucker very freely, just like the Albizia julibrissin, so this too can be a plant that can spread and pose a problem in your garden.

Mess dispersed below this tree may also be annoying for neat and tidy gardeners.

While both of these mimosa trees can bring benefits, neither may be the right choice for most UK gardeners.

Here are some alternatives to consider:

Other Flowering Trees

• Flowering Cherries
• Crab apples
• Amelanchier
• Magnolias
• Paulownia

Nitrogen Fixing Trees

Some good nitrogen-fixing options for growing in the UK include:

• Alders
• Common laburnum
• Laburnum x watereri
• Laburnocytisus adamii
• Caragana arborensis

Trees With Edible Yields

As well as the usual range of fruit trees including apples, pears, plums, cherries and more, you can also consider growing trees with edible leaves, such as:

• Hawthorn
• Lime / Linden
• Beech
• Birch
• Mulberry

Even if mimosa trees are not the right choice for your garden, you should still be able to find other trees which provide many of the same benefits, without the cons mentioned above.