when does mimosa flower in the uk?

The name ‘Mimosa’ is most commonly used to refer to two non-native tree species – Albizia julibrissin and Acacia dealbata, though, confusingly, neither of these is actually classified currently in 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.

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:

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.

One of the main reasons why this can be a very useful plant in many regions is that it is a nitrogen-fixing plant, which 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.

The variety ‘Rosea’ is hardier and more compact than other cultivars, and is the best choice for 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.

One other interesting plus point of this tree is that it is notably resistant to honey fungus.

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

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

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.

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.

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.

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.

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.

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.

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.

Like silk tree, silver wattle can only be grown without protection in milder parts of the British Isles.

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.

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:

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

At this time of year, when so much pink and white blossom is about, rounding a corner and coming upon a mimosa, with its masses of fluffy bright yellow flowers cascading from the arched branches, stops you in your tracks. Mimosas evoke a racy Thirties world of extended out-of-season stays on the Cote d'Azur. It seems to go with neatly pressed yachting clothes and lounging on teak steamer chairs. But some mimosas are pretty hardy, so you don't have to be very rich or live in the south of France to keep them happy.

Several will live in warm sheltered corners, while others will survive in cool glasshouses. The small spherical flowers, which grow in huge clusters, are actually made up entirely of stamens: mimosa flowers have no petals. Some mimosas have no leaves, either. The leaf-like structures are phyllodes, flattened triangular leaf stalks which grow straight on the branches.

Acacia dealbata, the silver wattle, is one of the easiest to obtain and easiest to grow in this country. It is the same one which is often seen by the side of the road in the south of France. The Mediterranean mimosas can blossom at other times, too. They have fern-like silvery leaves and their scent makes up for the rather harsh yellow flowers.

Acacia dealbata is worth trying in a sheltered spot anywhere in the south of England, where it can grow to 30 feet. In suitable conditions, mimosas grow fast: at Abbotsbury Sub-Tropical Gardens in Dorset they grow some species from seed - in less than a year these are three feet tall and ready to sell.

There are 1,500 different species of Acacia, all of which originated in Australia and Africa. Many need enough room to grow into a small tree, will sulk if they are cut down too much, and won't stand frost - so there is a limited choice for gardeners without double-height conservatories.

If you're on the trail of hardy mimosas you could try A retinodes. This is an attractive tree with narrow willow-like leaves, which flowers in late summer. But the best of all is probably A pravissima.

This is one which has phyllodes instead of leaves. They are silver-grey and arrow shaped, growing all along the branches, so they make good cut foliage even without the flowers. The flowers are a softer yellow than the silver wattle, and clusters of them are slightly smaller. They are spread all along the branches, so rather than making a solid block of yellow, the overall effect is of a mingled yellow and soft green. The branches flow in elegant arches, and seen from underneath, with a backdrop of a clear spring sky, the effect is totally magical. My plant flowered in January last year, but this year it is just about to flower as late as April, presumably because of the cold weather at the beginning of the year.

For a glasshouse, one of the best is A baileyana. It has frond-like, blue-grey leaves, and clusters of flowers in the early spring. Several nurseries now offer a cultivar, A baileyana Purpurea, which has a mauvish tinge to the young shoots. It needs the shelter of a conservatory, and a large pot of John Innes No 3, plus regular feeding. Acacias are part of the pea family, and produce a certain amount of nitrogen on their roots, so they don't need quite so much feeding as some other pot-grown shrubs. As Roger Clark, of Greenway Gardens near Brixham in Devon explained, they need well drained soil, and plenty of room to grow. If they are cut back too much it may prevent them from flowering freely.

As with many other plants, trial and error is proving that more and more mimosas will survive in this country. A flower which 20 or 30 years ago we expected to see only on holiday, is now being persuaded to thrive here. And as growers experiment with species, we can expect the range of mimosas to widen over the next few years.

Mimosa makes a beautiful evergreen shrub for the conservatory or greenhouse. It also makes an attractive small tree or shrub for sheltered gardens. The architectural silvery leaves are complemented by long, bobbly, fragrant yellow flower heads in late winter and early spring.