Grevillea - Cultivation

Introduction

With many different forms, growth habits and flower colours, grevilleas can be used for many different purposes in the garden. In addition, the flowers of many species and cultivars produce nectar and are excellent for attracting birds. Although grevilleas are popular garden plants, those species native to Western Australia are generally difficult to maintain for any length of time in areas of high summer humidity and rainfall (such as the eastern coastal strip of Australia). Similarly, eastern species may not thrive in the west.

Proteoid roots   
Proteoid roots can often be seen by carefully removing a proteaceous plant from its pot, as shown here.
Photo: Brian Walters

  

Like most members of the Protea family, grevilleas have a distinctive root system ("proteoid roots") consisting of tight groupings of many small "rootlets". These are believed to enable the plants to more efficiently take up nutrients from the nutrient-deficient soils where many of the species occur naturally. In cultivation this means that the plants can be adversely affected by fertilizers, particularly phosphorus. It is generally recommended that grevilleas and other Proteaceae be fertilised only with low-phosphorus, slow-release fertilisers or not be fertilised at all.

Virtually all species and cultivars perform best in well-drained soils and flower best in open, sunny positions. They prefer acidic soils.

Grevilleas respond well to regular, annual pruning where about one-third of the plant is removed. This promotes branching and produces a plant with a bushy shape. Some plants can be cut back severly if they develop a "straggly" shape. Some of the popular hybrids (eg G."Robyn Gordon", G."Honey Gem") are in this category. Others, however, will not tolerate this treatment. If in doubt, always leave some green foliage on the plant.

There are few serious pests that attack grevilleas. Borers may occasionally be a problem but will usually be noticed by the sawdust around the entrance to their tunnels. Inserting a piece of wire into the hole will often remove the pest, or the hole can be sealed with plastic wood. A variety of other pests such as caterpillars, sooty mould and scale may appear but they are no more of a problem on grevilleas than on any other plant and can often be ignored, allowing natural control methods (eg birds) to operate. If treatment is necessary, conventional pest control methods are suitable.

Allergic Reactions

The foliage of several grevilleas is known to cause skin irritations to individuals who are sensitive to compounds contained in the leaves. This occurs when the bare skin of sensitive individuals comes into contact with the foliage of the plants (contact dermatitis). Sensitivity varies considerably between individuals and between the different species and hybrids. The group of grevilleas most commonly impiclated in causing contact dermatitis is the "Robyn Gordon" group of cultivars. As these are very popular in cultivation, care should be exercised in locating these plants in the garden - it would be best to avoid locating them where people would need to regularly brush past the plants and it would also be best to avoid planting them in school playgrounds.

Further information can be found in the article "Grevilleas as Plant Allergens".


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