How to grow Acacia Dealbata
‘Acacia dealbata’ is a fast-growing evergreen shrub, commonly referred to as Mimosa or Blue Wattle. This acacia’s greyish-green foliage is finely divided, giving the leaf blades a fern-like quality. In winter and spring, bright racemes of fuzzy, yellow ball-like blooms cover the shrub. First used to make incense, the powdery, straw-like, honey scent of ‘Acacia dealbata’ has long been used in mainstream perfumes. In recent decades, there has also been considerable interest in the acacia’s ability to fix nitrogen levels and increase soil fertility. The flowers on this Australian native are nectar-rich, making the shrub highly attractive to bees and other pollinators. Maturing in 10-20 years, ‘Acacia dealbata’ will reach a height and spread of 12m x 5m. A winner of RHS’s Award of Garden Merit.
Key Information
Soil pH
Position
Hardiness
Where & when to plant Acacia dealbata
Initially, young ‘Acacia dealbata’ plants should be kept in containers in a frost-free environment until they have reached a reasonable size. Once well grown, your shrub can be hardened to outdoor conditions and can be planted out in areas of the UK with milder winters. However, in frosty weather, protect your shrub with fleece and add a good layer of dried leaf mulch around the base. In the garden, your shrub will require a sunny, sheltered position. Plant your acacia in well-drained, loamy or sandy soil which is acidic to neutral. A west or south facing location against a wall is ideal. This half-hardy mimosa can be planted all year-round, as long as the ground is not waterlogged or frozen. Alternatively, keep your acacia in a large container of loamy compost as a patio and conservatory plant which can live outdoors during the warmer, summer months.
How to plant Acacia dealbata
- Water your plant well while it is still in its container.
- Remove the shrub from the pot and gently tease out any matted roots.
- Dig a planting hole the same depth and at least 3 or 4 times the width of the root mass.
- With a fork, loosen compacted soil on the base and sides of the hole. Mix a good quantity of compost into the soil in the hole.
- Young acacia plants require moist, soft soil, so fill the hole with water a couple of times and allow the water to drain away before planting.
- Place the shrub in the centre of the hole and fan out the roots. Back fill the hole with soil, taking care not to leave air pockets.
- Firm the soil gently and water to help settle the earth around the shrub.
- A mulch around the plant is a good idea, however, keep mulch 10cms away from the plant’s base to prevent rot.
- Stake your ‘Acacia dealbata’ firmly and keep the shrub well-watered when first planted.
What to plant with Acacia dealbata
Direct attention to this architectural shrub’s glorious blooms by combining it with plants which flower in summer, after your acacia has finished blooming. Good choices are other spreading shrubs with contrasting leaf structures to your acacia’s delicate ferny foliage. As a patio plant, group your ‘acacia dealbata’ with other southern hemisphere natives to create a fascinating antipodean garden.
If you would like any further planting ideas or growing advice for your ‘Acacia dealbata’, please contact our friendly and knowledgeable Customer Care Team - we will be more than happy to help you.
How to care for Acacia dealbata
Pruning and Deadheading
Never trim this plant in winter as your acacia will not flower the following season if you do so. In general, these shrubs do not respond well to excessive pruning, so shape the tree while it is young and avoid excessively pruning the mature plant. ‘Acacia dealbata’ are best pruned in mid-April.
Standard Tree
To grow your acacia as a standard tree, pruning will be needed to shape the tree during the first 5 years.
For the first 3 years, prune your young shrub in three clear divisions. Generally, leave the top third of the tree alone, only remove any dead, diseased or badly placed growth. In the middle third of the tree, halve the length of all the side shoots. Cut these shoots just above a node which directs new growth in an outward direction. Finally, on the lower third of your shrub, completely clear the main stem of all side growth.
In the 4th and 5th years, continue to clear the main stem (lower third) of all side growth until the tree’s trunk fits your requirements. Always remove dead, diseased or badly placed stems on the top two thirds of the tree.
Once mature, only lightly prune your acacia, removing dead or diseased branches.
Multi-branched shrub
After the first year of growth, cut back the main stem of the young plant approximately 8cm from the ground to encourage the shrub to spread.
By the second year, multiple stems should have appeared. Cut all these stems back to the base except for 3 or 4 sturdy specimens which are nicely spaced.
In the third and fourth years of development, the main stems you retained should develop side shoots. When pruning, remove low hanging side shoots and any new stems growing directly from the base. If necessary, also thin out the side shoots in places where new growth is too crowded.
Once the shrub is mature, remove dead or damaged branches after flowering and thin out crowded growth. Side shoots can also be trimmed. Cut these 2 or 3 buds below the spent flowers.
Watering
‘Acacia dealbata’ are considered drought tolerant, although your shrub will require a weekly watering in summer until fully established. When planted in the garden, your mature shrub should only need watering every few weeks during hot weather. Acacias kept in containers should be watered regularly. Keep the soil moist, not drenched, and ensure there are adequate drainage holes to avoid water-logged soil.
Cold Protection
In frosty conditions, protect your young shrub by wintering container plantings in a conservatory, or covering immature garden shrubs with horticultural fleece.
Pests and Diseases
‘Acacia Dealbata’ can occasionally be susceptible to glasshouse red spider mite, fluted scale and mealybugs, although it is mostly disease free.
How to propagate Acacia dealbata
‘Acacia dealbata’ can be propagated from semi-hardwood cuttings (and seed). Below are instructions for taking semi-hardwood cuttings from your shrub.
Take your cuttings in the early morning after flowering has finished. Select shoots which are healthy and free from disease. The shoots must have hardened but still have a soft tip from the new summer’s growth. Using a knife or secateurs, cut diagonally across stems just below a leaf to take cuttings of 10-15 cm. Place the cuttings in a plastic bag and keep them in the shade. Pot them out within 12 hours.
Trim your cuttings just below a lower leaf node and pinch out the tip. Remove all except 4 of the leaf blades on your cuttings. Be careful not to tear the bark while doing so. Trim down the remaining leaf blades a little to stimulate your cuttings’ growth hormones and reduce water loss. You can simply cut off half of each leaf blade if you prefer. Dip the base of each cutting in hormone rooting powder and gently tap off any excess.
Plant your cuttings in pots with a mix of 50% cuttings compost and 50% sand or perlite. Remember to label your cuttings with the plant name and the date taken. Water the cuttings well and either store them in a greenhouse or cover them with plastic bags. Initially, keep these young plants in good light (away from direct sunlight) and then gradually introduce the plants to gentle sunshine. The soil should be kept moist. Monitor root growth and pot on as and when required. Harden off the young plants gradually before planting them out.
Common Acacia dealbata questions
What temperatures can an ‘Acacia dealbata withstand?’
This shrub can withstand brief cold spells. It is most suited to milder parts of the UK with temperatures no lower than -5 to 1°C.
Why is my ‘Acacia dealbata’ not flowering?
If a healthy and well-watered shrub is not blooming, then it is likely the plant is not mature enough yet to bear flowers.
What does the name ‘acacia’ mean?
Acacia is derived from the Greek term ‘akakia’ which refers to a ‘thorny plant’.