What are Banksias, and How do you Grow them
There are over 70 species of woody trees and shrubs; plus 15-16 recognized sub species. They are used mainly in shrubberies for foliage or flower effects, or for cut flowers. Some grow well in tubs. Some suit small gardens, others do not.
The most popular cut flower species is B. coccinea. Others are grown cut flowers (and in some cases cut foliage), include: B. prionotes, B. hookeriana, B. burdettii, B. victoriae, B. baxteri, B. menziesii, etc.
B. ashbyi is particularly popular as a cut flower in Israel.
Flower heads are brush like, usually colourful, and large. Most Banksias produce flowers on the sides of stems (in which case, the leaves partially hide the flowers).
Some however, flower on the ends of stems (terminal flowering), which makes the flowers less obscure both on the plant, and a better selection as a cut flower.
Leaves dry and stiff, often with serrated edges (not always), and lighter colouring on underside.
Soil must be well drained for most varieties, particularly those from Western Australia. Most popular varieties prefer sandy soils. Banksias generally prefer an acidic soil, though many of the West Australian species grow on acidic top soils with alkaline sub soils.
Most grow fast, though some varieties may be slow. Transplanting larger plants is very difficult.
Plant on slopes, in raised beds or sandy soils. Do not feed with fertilisers containing phosphorus.
Responds well to iron (place some rusty nails around plants). Do not over-water.
Most are highly susceptible to cinnamon fungus (ie. Phytopthera cinnamomi).
Limestone underlay technique (ie. building a bed of acidic soil over the top of a layer of agricultural lime), has proven useful to enable more difficult W.A. species to grow outside of their natural habitat.
Propagation is normally by seed. Collect seed cones when seed is ripe, but before seed drops (for some varieties this is easy, for others, there is a relatively short period when seed can be collected). Seed remains viable longer if stored in cones (but cones can be prone to insect attack and may need to be treated with a pesticide). Store seed cones in a cool place. When ready to plant, place cones in a warm place for them to open and release seed. If seed does not release easily, soak the cone in water for 2 days then place in a warm place immediately. Day temperatures of 20 to 25 degrees Celsius are best for seed germination. They are best left in a pot of seed raising mix in the open or an unheated greenhouse (do not place in a heated greenhouse). Damping off diseases can be a problem during early growth, and should be closely watched. Germination can take 3 weeks to 3 months. Some species can be grown from cuttings (mainly the fine leafed types such as Banksia ericifolia).
There are few pests & diseases. Banksias are very hardy in cultivation if conditions are appropriate, however many West Australian species have difficulty adapting to soils and climates beyond their natural area, but can do well if grafted onto hardier species.
If drainage is likely to be a problem, try to grow them in raised beds, on mounds, slopes or in sandy soils. Consider growing them even in pots. Many of the West Australian species prove difficult to grow in the eastern states of Australia or other parts of the world; it would appear partially because of higher humidity, and partially due to soil conditions. Those that have been grown successfully must usually be provided with excellent drainage, sometimes lime in the soil, and good ventilation (do not crowd amongst other plants).
Success has also sometimes been achieved by using Eastern species as a rootstock and grafting the WA species onto a root system that better tolerates wet and sometimes acidic soils.
Though Banksias are particularly susceptible to fungal diseases, pest problems are relatively little.
Cinnamon Fungus (Phytopthera cinnamomi) is perhaps the most serious problem. Most Banksias are highly susceptible! Other diseases which Banksias are susceptible to include:
Other species of the fungus Phytopthera, Grey Mould or Flower Blight (Botrytis cinerea)
Shoot Tip Blight (Drechslera spp.), Anthracnose, Armillaria root rot, Verticillium Wilt
Damping Off (in seedlings), Scab or Cork Bark (Elsinoe spp.), Silver leaf (Chondrostereum purpureum)
White Root Rot (Rosellinia spp.), Bacterial Leaf Spot
Pest problems though relatively few, can include: Root Knot (caused by a nematode), Caterpillars (attacking the flowers or occasionally leaves), Beetle damage to leaves, Birds eating seeds (mainly parrots & cockatoos), Insects eating seeds.
B. baueri -2m X 2m, large furry orange flowers winter-spring.
B. baxteri -3m tall and 2m spread, yellow flowers in summer, grows well in Adelaide on an acidic sand over a limestone sub soil, has been flowered successfully as far north as Sydney.
B. brownii -2m tall and 3m spread, red/gold flowers autumn-winter.
B. caleyi -2m X 3m, prickly foliage; yellow or red flowers spring-summer. Grows well as a grafted plant in Victoria, but results are unreliable in NSW.
B. conferta -3m X 3m, yellow flowers summer-autumn, cultivation has been limited, but some success has been reported on east coast Australia.
B. dryandroides -1m X 1 to 2m, brown flowers spring-summer, has been grown successfully in Melbourne and Sydney in a partly shaded position, with perfect drainage in a rockery.
B. ericifolia –hardy variety, can get to 4 X 4m, but there are different varieties, some varieties have smaller “candles” (flowers), or grow smaller; one variety is prostrate.
B. laricina -2m X 3m, yellow flowers in winter, needs well drained spot, very decorative sought after cones.
B. nutans -1 to 2m X 2m, brown to purple brown in spring and summer.
B. occidentalis -3m X 1.5m, red-gold flowers late summer-autumn; reasonably adaptable in eastern Australia, has been grown successfully in Hawaii, excellent results if grafted onto B. integrifolia.
B. spinulosa -3m X 3m, rich yellow and black flowers.
B. robur -suited to coastal areas from warm temperate into sub tropics, to around 2m tall, very hardy, growing successfully from tropical north Qld to southern Victoria, but best in sands or at least well drained soils.
A number of selected cultivars are in increasingly wide cultivation, particularly varieties of B. ericifolia, varying in shape and growth habit. One variety is even largely prostrate.
‘Giant Candles’ is suspected to be a hybrid that emerged accidentally from B. ericifolia and B. spinulosa. It is a medium shrub with particularly stunning flowers. This cultivar is only propagated by cuttings (in order to ensure required characteristics are carried over to the new plants).
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