With the arrival of March there are many plants bursting into bloom and vying for your attention. One that will always catch your eye is Acacia pravissima which makes a shapely, large shrub or small tree. Its flower buds begin to form in mid winter, giving the plant a gentle yellow haze and as the feathery flowers slowly open they turn bright yellow to produce a stunning effect. This acacia is not completely hardy but it has been growing at RHS Garden Hyde Hall for 10 years and it has survived temperatures down to -9. It prefers to be grown in a warm, sheltered situation and does well in our south-facing Dry Garden where the soil is free draining.
- Common name
- Oven’s wattle
- Height & spread
- 3-8m (10-25ft) x 3-7m (10-22ft)
- Evergreen shrub or small tree
- Moderately fertile, neutral to acid
- Full sun
- Half hardy (can withstand temperatures down to 0C (32F) or a little lower
Acacia is a very large genus of trees and shrubs found in many tropical and warm temperate regions, but especially Australia and Africa. Acacias occur naturally in an extraordinary range of habitats from sea level on coastal plains to high sub-alpine zones and from arid climates to high rainfall regions at the rainforest margin.
The apparent leaves of many acacias are not actually the true leaves. In many species the leaves become much reduced and 'disappear' after the seedling stage to be replaced in form and function by phyllodes - flattened leaf stalks, which appear like, and serve the same function as leaves.
The many yellow stamens are the most conspicuous feature of the flowers, varying in shade from bright to very pale. The flowers are borne in clusters or in cylindrical spikes, which look like miniature bottle brushes.
Many species have sharp thorns to protect the foliage from browsing animals. In Africa the acacias are commonly referred to as thorn trees.
The common name, wattle, came from the early Australian settlers who would build houses using the 'wattle and daub' method. They would use the abundant, pliable Acacia branches to weave the wall, which was then covered with mud.
This half-hardy species is found growing in the hills of south-eastern Australia.
It is a small tree or spreading shrub with pendant branches and small, triangular, grey-green phyllodes, 0.5-2cm (0.25-0.75in) long. The name pravissima means 'very crooked', referring to the phyllodes.
Flowers are produced in spring, and have profuse, fragrant, bright golden yellow, spherical, fluffy flowerheads, 5mm (0.25in) across.
The prostrate form ‘Golden Carpet’ spreads to 4.5m (15ft). Acacia pravissima is a good tree for a small garden, if adequate shelter can be provided.
- Acacias are susceptible to frost so only grow them outside in areas with relatively mild winters. Frost hardiness seems to increase greatly with age. Temperatures much below -10ºC will kill most specimens very quickly.
- Grow outside in a fertile, neutral to acid soil in a sheltered position in full sun. In areas at the limits of hardiness, plant near the base of a sheltered south facing wall.
- Under glass grow in direct sun in free-draining compost. Water moderately when in growth and sparingly in winter ensuring that a liquid feed is applied at fortnightly intervals. They flower more freely if placed outside in summer after the danger of frost has passed.
- Regular pruning is not necessary except for pot-grown specimens. Established plants resent hard pruning.
- Grown under glass, acacias can become infested with a wide range of glasshouse pests including tortrix moth, scale, red spider mites and mealybugs which should be treated accordingly.
- If grown outside they are relatively pest free, though any damage caused by frosts should be pruned out to stop any infections.
- Acacias are easily raised from seed but take semi-ripe cuttings of cultivars.
- Sow seeds in spring at 20-25ºC (68-77ºF) when they will take between one and three weeks to germinate if the dormancy mechanism has been broken. To break the dormancy mechanism, naturally triggered by fire, soak the seeds with scalding water and allow them to soak in the cooled liquid for up to 48 hours before sowing the viable swollen seeds.
- Semi-ripe heel cuttings should be taken in summer. Use a sandy propagation mix and provide a gentle bottom heat at 16-18ºC (60-65ºF) for the best results.
The RHS Woody Plant Committee awarded Acacia pravissima an Award of Garden Merit on account of its good foliage and flower.