Acacia dealbata

Acacia dealbata

Common Names

Silver Wattle, Mimosa

Family

Fabaceae

Description

Fast-growing shrub or tree, leaves are blue-green to silvery-grey, rich yellow nectar flowers are enjoyed by bees, susceptible to frost. Popular as an ornamental street tree in Mediterranean countries but does not grow as well in cooler climates further north.

foliage	flowers
File:88 D.jpg bark	File:88 E.jpg fruit	File:88 F.jpg nut

Foliage	evergreen
Group	broadleaf
Toxic Parts?	no
Height	15 - 25m
Crown Diameter	8m
Crown Shape	variable
Shade Tree?	no
Autumn Colour?	no
Age	30-40 years
Time to Maturity	- years
Flower Colour	yellow
Fruit Colour
Bee Friendly?	yes

Native Areas

Native to southeastern Australia in New South Wales, Victoria, Tasmania, and the Australian Capital Territory.

Preferred growing conditions

Soil pH Range	5 - 7.5 (acidic - slightly acidic - neutral )
Soil Types	sand, silt, clay, loam, chalk
Drainage	well drained
Soil Fertility	medium
Sunshine	part sun and full sun
Soil Moisture	moist
Tolerates Exposure	no
Growth Rate	- fast

Hardiness

RHS	USDA	EGF
	10

How to plant

Water container-grown and rootballed trees well and allow to drain an hour before planting. While it drains dig out an area for the tree that is about 2 to 3 times the diameter of the container or rootball and the same depth as the container or rootball. If the soil is compacted loosen with a fork (this includes the sides of the hole). But beware of having soil that is too loose on the bottom as this will cause the tree to be lower than desired upon watering.

• If container-grown, put the tree on its side and remove the container. Place in the hole and loosen the roots around the edges without breaking up the root ball too much. Check the depth by place a cane or stick across the diameter - only the root collar should be below and not the main stem.

• If planting a balled and burlapped tree, remove ties or nails from the burlap at the top of the ball and using a knife if necessary, pull the top of the burlap back, so it does not stick out of the hole when the soil is replaced. Synthetic burlap should be completely removed as it will not decompose. Note burlap sticking out of the hole can wick water away from the tree.

• For bareroot trees, feel the moisture of the roots by hand - if dry, dunk them in an bucket of water for 10-15 seconds and replace the packaging (if you are not going to plant at that time). Do not plant too deeply - only plant up to the root collar. i.e. the stem should not be covered in soil. Ensure roots are planted firmly and have good contact with the soil.

Fill in the hole with soil and compost, but do not add less than half of the original soil.

Using the soil, create a water ring around the outer edge of the hole. Not only does this conserve water, but it will also direct moisture to the perimeter roots, encouraging outer growth. Once the tree is established, the water ring may be levelled. Studies show that mulched trees grow faster than those unmulched, so add a 3 inch layer of pinestraw, compost, or pulverized bark over backfilled area.

Only prune lower damaged branches if necessary. Water newly planted trees regularly in their first year. Staking is also important in new trees and in exposed areas - a 1 m stake at 45 degrees crossing the stem at a height of 15 cm can provide good support. Be careful of the binding of the stake to ensure the tree is not strangled. Binding should be checked in the second year, as the stem will thicken.

When to plant

Container grown trees can be planted at any time of the year, but be sure there is suitable light and the area is not too cold. Frost will damage mimosa. It has been known to flower more plentifully if put outside in summer after the frost has passed.

Tree care

Hedging Potential	no
Balcony/Roof Terrace	no
Indoors	no

Potential Pests and Diseases

Pests	galling insects
Diseases	fungal galls

Ecology

Considered an invasive species in several countries, especially South Africa. In its native habitat it provides food and habitat for fauna and fixing atmospheric nitrogen.

History and Human Connection

In Europe, A. dealbata was introduced around 1816 where acacias (‘mimosa’) are grown for horticultural and floricultural purposes. The ‘mimosa’ cut flower industry in France occupies around 200 ha with an estimated value of €3–4 million/year.

Uses

• As an ornamental tree in warm temperate regions
• Its timber is used in craft furniture work
• Flowers are used ornamentally (mimosa)
• Flower essences provide a base for perfumes (opopanax)
• Leaves can be used to make chutney
• In Australia, A. dealbata is utilized in habitat restoration programs and urban landscaping projects

References

• List of Trees