Acacia dealbata, the winter mimosa tree

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Golden yellow blooms smother the evergreen foliage at the heart of winter, releasing a fresh, appealing scent. The winter mimosa tree (Acacia dealbata) is grown for exactly that midwinter colour and fragrance, and it asks only for full sun and sandy, well-drained soil — meet that and the perfume drifts right through the neighbourhood.

Planting Acacia dealbata

Plant this indifferently in spring or fall in a sunny spot and, ideally, sheltered from wind. Note also  that Acacia dealbata tolerates slightly windy spots.

The acacia dealbata tree thus likes rather sun-endowed emplacements and especially well-drained soil.

• Acacia dealbata is especially suited to the Mediterranean area and along the Atlantic coastline.
• You’ll have to avoid heavy clay soil.
• In chalky soil, select a grafted tree for which the root stock will be better suited to that particular soil type. Acacia retinodes (also called swamp wattle) is a great choice for the root stock.
• Follow our guidance on how to plant your Acacia dealbata shrub.
• Propagate your A. dealbata tree through cuttings in summer.

If you choose to grow your acacia dealbata in a pot for a deck, balcony or terrace, its fragrance will spread in the entire vicinity as soon as the first flowers open.

Actually, in regions with harsh winters, it’s better to plant Acacia dealbata in pots or large containers so that you may bring the shrub indoors over winter.

Acacia dealbata in winter

The Acacia dealbata tree can resist freezing, if moderate. 23°F (-5°C) is the coldest temperature it can survive, especially when bouts of freezing only last a short while.

When in pots, this Acacia isn’t as hardy to the cold, so bring it indoors for shelter in a cool spot over the winter if it freezes in your area.

• You can also put horticultural fleece to good use, wrapping it around the branches at the onset of the first frost spells. This will be very effective in protecting the mimosa tree from freezing.
• Also protect the base with a good layer of dried leaf mulch.

When growing directly in the ground and if the weather freezes deeply in your area, protect your tree by implementing our advice on protecting plants against the cold.

Pruning and caring for Acacia dealbata

Pruning of your A. dealbata takes place after the blooming because if you cut the tree in winter, you won’t have a single flower.

• Lightly cut back branches that have born flowers.
• As soon as they appear, pinch off suckers that shoot out at ground level, because these will weaken the rest of the tree.
• If your Acacia dealbata is grafted, remove any suckers that emerge from the root stock.
• Detailed run-through on how to prune Acacia dealbata

If, at the end of winter, you notice broken and blackened branches because of freezing, feel free to cut them off because they, too, would weaken the tree.

• Never cut back into thick, leafless old wood, because Acacia dealbata rarely reshoots from it.
• Shorten each flowered shoot by no more than a third, cutting just above a leaf, so the crown stays bushy instead of bare and leggy.
• Snip off the flat seed pods that follow the blooms: this wattle self-seeds freely.
• If frost kills the top, wait for shoots to rise from the base before giving up on the tree, but on a grafted plant rub out anything appearing below the graft union.

Watering acacia dealbata

Acacia dealbata isn’t a tree that requires much watering, except if potted.

It hates excess moisture which has a tendency to rot roots, eventually killing the tree.

Watering acacia dealbata planted in the ground

You must water in case of prolonged dry spells, but otherwise stocks of water contained in the tree itself should answer the acacia dealbata tree’s needs.

Watering acacia dealbata planted in pots

Mimosa trees grown in pots demand regular watering which should be moderate in quantity over winter and provided only when it isn’t freezing.

In summer, and in case of hot weather, water in the evening to avoid having the water evaporate immediately.

• Water a newly planted Acacia dealbata regularly through its first summer, since the roots need a full growing season before the tree can fend for itself.
• Empty the saucer under the pot after every watering.
• Between waterings, push a finger into the compost and only water again once the top feels dry.

Diseases, pests & problems with Acacia dealbata

A very vigorous tree, Acacia dealbata is only rarely subject to disease.

Acacia dealbata dripping sticky sap from bark

After a heat wave, if it rains or too much water is provided, sometimes the tree builds up excess pressure in its trunk and stems. Too much sap and water swell up from the root system.

To avoid bursting entirely, special cells along the trunk wall break open and release extra pressure. These act like natural valves or nozzles that ooze out a sticky, sappy substance. This is called gummosis.

It’s a healthy sign when it only occurs occasionally. If it repeats often, perhaps the growing conditions of the tree should be looked at.

• Although this substance is mostly water, you should rinse it off with a hose. If not, you’ll risk stains on your car, concrete driveway, or pavement.

In a way, this is a similar process to that of guttation, where plants start weeping tears from leaves.

All there is to know about the acacia dealbata

Acacia dealbata is famous for its superb golden yellow blooming that decorates gardens and decks at the heart of winter or at the beginning of spring.

Its foliage is evergreen and its blooming has a fresh, appealing smell.

The middle of winter is when this tree drapes itself in full color, and releases its distinctive odor throughout the neighborhood.

You can highlight Acacia dealbata’s perks on your terrace or deck if you plant it in a large garden box and water it as soon as the soil turns dry.

Acacia dealbata was introduced in Southern France in 1820 and over 1200 mimosa tree species have been numbered throughout the world.

Note that there is a certain confusion in terms: the tree that is commonly called Mimosa tree is actually an Acacia, whereas the tree that is commonly called acacia is really the locust tree.