<em>Grevillea</em>: planting, pruning and care

Description and botany

Genus Grevillea comprises nearly 250 species of trees or bushes, sometimes creeping, with highly variable evergreen foliage. It belongs to family Proteaceae, widespread in South Africa and including genera Protea, Banksia, Hakea, Telopea, Leucodendron. Grevilleas are mainly native to Australia with a few specimens in New Caledonia and Papua New Guinea. They are pioneering plants with rapid growth, growing in wooded areas, moist forests and clearings. They tolerate fairly poor dry soils but dislike calcareous conditions, and require full sun to flower. Size ranges from 30 cm to 35 m tall (G. robusta) with habits from erect tree-like to bushy, dense or creeping.

Leaves have a lamina with reduced surface area, either needle-shaped as in Grevillea juniperina or rosmarinifolia, slightly broader with revolute margins in G. olivacea (olive-leaved), fern-like finely divided fronds (bipinnate) as in Grevillea robusta (15 to 30 cm long) or ‘Robyn Gordon’, or short succulent leaves as in Grevillea lanigera ‘Mount Tamboritha’. Foliage colour ranges from light green to dark green and silver. In all cases, the leaf shows adaptations to drought whether by a waxy layer on the upper surface, hairs on the underside, succulence, etc.

Grevillea oleoides – botanical illustration

Grevilleas generally display abundant, very exotic flowering in an arachnid-like form, with reduced tepals rolled like snail shells opening to reveal 4 stamens at their tip and 1 long protruding pistil curved like a pin before opening. Terminal inflorescences form in some species such as robusta unilaterally arranged spikes reminiscent of a toothbrush; others are cylindrical and others globular. Flowers sometimes appear directly on the trunk (cauliflory). Flowering offers a wide palette of colours: red, pink, orange, yellow, white. The flowering is highly nectariferous for birds and insects, a boon as it lasts a long time, often starting in winter followed by a burst of flowers in spring and a repeat in autumn. Bushes grow very rapidly and reach adult size within 3 years. Flowering occurs from the second or third year after sowing.

Botanical species produce a lignified and hard fruit that opens at ripeness. Cultivated Grevillea produces relatively few fruits compared with number of flowers and hybrids are often sterile.

Wood of the tree species Grevillea robusta is valued for furniture making.

Warning: some species of the ‘Robyn Gordon’ group in particular cause allergic reactions on contact in some sensitive people.

Grevillea juniperina

Main varieties of Grevillea

Varieties with needle leaves

Varieties with broad leaves

Variety with creeping habit

Grevillea rosmarinifolia

Arguably most widespread Grevillea thanks to good cold hardiness (-15°C) and ease of cultivation. Its narrow bright-green foliage is studded with frilly bright-red inflorescences for many weeks from February to May. Resistant to disease and drought.

• Flowering time March to July
• Height at maturity 2 m

See the product sheet

Grevillea Canberra Gem

A hybrid between juniperina and rosmarinifolia, Grevillea 'Canberra Gem' has a dense habit up to 2 m in all directions and needle-like sharp light-green leaves studded with red flowers from March to July. Hardy to about -10 to -12°C.

• Flowering time April to August
• Height at maturity 2 m

See the product sheet

Grevillea johnsonii

It bears long, fine leaves reminiscent of dark-green pine needles. Delicate flowering occurs from late winter to late spring as erect terminal clusters composed of curious bright-pink, cream-washed flowers coiled like snail shells and topped by long styles. An excellent bush for borders or hedging in coastal gardens (-11°C) or for container growing.

• Flowering time April to August
• Height at maturity 3 m

See the product sheet

Grevillea rosmarinifolia Rosa Jenkinsii

Compact variety ideal for containers, with very ornamental light-green foliage and a beautiful bright-pink spring flowering. Resistant to disease, drought and cold (to -10°C in well-drained soil); perfect by the sea, in a flowering hedge or as a specimen.

• Flowering time April to October
• Height at maturity 1,30 m

See the product sheet

Grevillea rhyolitica

Rare Grevillea species presenting lanceolate foliage. Its slightly trailing inflorescences of coral-red tubular flowers somewhat resemble those of Embothrium. Rounded compact habit suits container growing well. Not very hardy (-5°C).

• Flowering time March to October
• Height at maturity 2 m

See the product sheet

Grevillea lanigera Mount Tamboritha

Creeping bush forming an attractive groundcover with leathery grey-green succulent foliage with a slightly wooly appearance, spreading to about 1.5 m across. Pink and cream flowering from late winter into spring brings a soft touch to borders and rockeries at a time of year when flowering bushes are still scarce. Hardy to -10°C in acidic to neutral, well-drained soil.

• Flowering time March to June
• Height at maturity 15 cm

See the product sheet

Planting

Where to plant Grevillea?

Most Grevillea do not tolerate temperatures below -5°C. Their cultivation is therefore limited to coastal areas of the Atlantic or Mediterranean. The hardiest species, rated to -12 to -15°C, include Grevillea rosmarinifolia, as well as cultivars such as G. juniperina Camberra Gem tolerating down to -10/-12°C with peaks to -15°C, and less commonly grown species here such as G. australis, G. diminuta or G. victoriae.
Plant Grevillea in full sun, possibly with light shade if you are in the Midi to encourage generous flowering.
They prefer well-drained soils with low nutrient content, acidic to neutral except for species robusta which tolerates calcareous soil.
Regarding winter hardiness, everything of course depends on other environmental factors: soil type, moisture level, duration and frequency of frost periods, presence of protective elements near the plant, such as other plants or a wall, for example…

When to plant?

Plant Grevillea preferably in spring to avoid exposing it to freezing temperatures before it is established.

How to plant?

This plant establishes and grows very quickly if climate and soil suit it, but it also grows very well in a container.

1. Dip the bucket into a bucket of water to thoroughly moisten it.
2. Dig a hole three times wider than the rootball and loosen the soil around it with the tines of a digging fork.
3. Add a few handfuls of sand and gravel to ensure good drainage around the roots. In heavy soil, opt for planting on a raised mound or within a rockery.
4. Place the plant in the planting hole.
5. Replace the soil and firm lightly.
6. Water.

In a container, make a mix of potting compost, heather soil and sand and choose species with compact growth such as rhyolitica or Jenkynsii. Potting compost must be very well drained, yet retain enough water. A good mix can also approximate this composition: 60% pine bark, 20% coarse river sand, 10% fine river sand and 10% clayey soil to retain water. pH must be below 7.

→ Find out more in our advice sheet: Growing Grevillea in a pot

Grevillea ‘Robyn Gordon’ in situ

Pruning and care

Monitor watering during first summers to stimulate establishment and vigour of plant. However avoid any excess water; soil should dry out to about 1 cm depth between waterings. Avoid using hard water, which causes leaf yellowing.

Cover plant with horticultural fleece to protect from cold if necessary but above all to prevent excess water at relating to root level.

On poor soil, mulch base of Grevillea in autumn with debris to a depth of 8 to 10 cm (dead leaves, shredded twigs, grass clippings). Plant thus produces a dense superficial mass of root hairs capable of capturing maximum minerals and water contained in humus.

In pot, feed with a low-phosphorus fertiliser (P) such as 18-2-10 so as not to reduce flowering. Take care not to subject it to severe drought stress that can kill it suddenly, while also avoiding stagnant water in saucer. During winter let it dry out to about half pot height (a terracotta pot makes it easier to visualise moisture level). Consider repotting in spring, especially initially, then simply renew surface compost of pot.

Pruning of Grevillea

Reduce shoots by one-third of their length after flowering or during growth period if you wish to keep plant more compact.

Potential diseases

Grevillea are rarely diseased except for shoots sometimes drying out or becoming covered with black spots after fungal attacks. Promptly prune dead shoots, open up base of bush so it is not buried and protect it from excess moisture. Apply a copper-based fungicidal treatment to spotted foliage.

Phytophtora cinnamonii which affects many Australian and native plants is active during wet winters by blocking sap-conducting vessels. When first warm weather arrives bush suddenly desiccates partially or entirely. Watering soil with a systemic fungicide such as Aliette reduces its impact.

Yellowing of foliage is often due to excess lime in soil or in water used for watering.

Propagation

Multiplying Grevillea is fairly tricky, both propagation by cuttings and sowing. You can try sowing after scarifying seeds or by separating suckers when plant is producing suckers.

Sowing

1. Scarify seeds with sandpaper or soak seeds in water for 24 hours.
2. Sow seeds in a tray or in cells filled with seed compost moistened the day before. Cover with a thin layer of vermiculite and place in indirect light.
3. Place in a mini greenhouse maintained between 10 and 15 °C, in indirect light until seeds germinate.
4. Prick out into bucket as soon as you can handle seedlings without disturbing roots too much.

Uses and companion plants

In an exotic or Mediterranean garden on neutral to acidic soil, it can be included in a large rockery planted with structural, upright plants such as Agave, Beschorneria, Aloe, Cordyline australis, Canary viper’s-bugloss (Echium pininana), palms, combined with more massive forms such as Euphorbia mellifera, Protea, evergreen Ceanothus, Melianthus major, Euryops, Callistemon and Leptospermum. The creeping form Mount Tamboritha can cover rocks in the foreground while other Grevillea species are better placed at the back of the bed or at the very top of the slope.

An example of a combination: Ceanothus ‘Skylark’, Grevillea ‘Robyn Gordon’, Leptospemum scoparium ‘Martini’, Euphorbia mellifera (photo H.U. Küenle)

Grevillea generally form masses of interlaced, quite spiky branches that make impenetrable hedges, flowering for a very long period, within 3–4 years. This essential oil, sun-loving, robust and tolerant of sea spray and requiring quite poor soil, grows perfectly by the seaside.

In containers, pair it with Mediterranean plants such as Cassia florinbunda, Cape Plumbago, Leptospermum, Caesalpinia gilliesii, Sesbania punicea, palms and citrus trees which you will bring into an unheated greenhouse or a very bright, lightly heated conservatory over winter.