Treating Sick Bottlebrush Plants: Learn About Diseases Of Bottlebrush

By: Teo Spengler

Few plants fit their common names better than bottlebrush shrubs. The spikes of flowers, so attractive to hummingbirds and butterflies, look exactly like the brushes you might use to clean a baby’s bottle or a narrow vase. These eye-catching plants are generally vital, healthy shrubs, but occasionally bottlebrush diseases strike. If you have sick bottlebrush plants, read on for helpful information about bottlebrush disease treatment.

About Sick Bottlebrush Plants

Gardeners love bottlebrush plants (Callisteman spp.) for their brilliant blood-red flowers, evergreen foliage, and easy-care ways. These shrubs are so vital that they can become invasive if left to their own devices. But that doesn’t mean that you won’t have to deal with a few diseases that attack these bushes. If you know the signs of different bottlebrush diseases, you’ll be able to jump right into bottlebrush disease treatment.

Diseases of Bottlebrush

The most common bottlebrush diseases include both easy-to-remedy problems, like twig gall or mildew, and serious issues like root rot and verticillium wilt. Many of the issues are caused by excessive moisture in the soil or on the foliage of the plants.

For example, wet soil is the direct cause of twig gall, a fungal disease. If you see many new twigs growing from the tree and branches that bloat, the shrub may have twig gall, one of the most common bottlebrush diseases. Cut off the unhealthy growth and dispose of it, then correct the overly wet soil.

Powdery mildew is also one of the diseases of bottle brush caused by too much water. But the main cause of powdery mildew is water on the foliage. Bottlebrush disease treatment for powdery mildew is fungicide spray, but you can prevent a reappearance by watering the shrub from below, not above.

Both root rot and verticillium wilt are serious bottlebrush diseases that are difficult or impossible to treat. Both are caused by fungus.

Root rot results from too much water in the soil. Bottlebrushes need well drained soil, not wet soil. When the soil is too moist, the root rot fungus can attack the shrub’s roots as well as the plant’s neighbors. You’ll see the branches dying back, leaves yellowing and falling, and the trunk turning strange colors. Bottlebrush disease treatment here is applying fungicides, but it’s much easier to prevent this disease than to cure it.

Verticillium wilt is another of the diseases of bottlebrush that causes yellowing leaves and branch dieback. It is not likely to kill bottlebrush plants, but it is hard to rid the soil of the fungus. Your best bet is to treat the area with fungicides and move the tree to another location.

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Root Rot

Poor soil conditions and over-watering combine to kill bottle brush trees through root rot. Caused by several different fungi, root rot affects stressed roots, especially those that are in soggy soil. Because roots cannot absorb oxygen from the soil, they slowly die, allowing fungi to proliferate across the entire root structure. As a result, moisture and nutrients cannot reach the stems and leaves. The leaves turn yellow as chlorophyll degrades. Bottle brush trees easily succumb to root rot if soggy conditions persist because leaves eventually drop -- no photosynthesis can be performed and the tree dies.

Common Bottlebrush Diseases - Learn About Bottlebrush Disease Treatment - garden

The flower spikes of bottlebrushes form in spring and summer and are made up of a number of individual flowers. The pollen of the flower forms on the tip of a long coloured stalk called a filament. It is these filaments which give the flower spike its colour and distinctive 'bottlebrush' shape. The filaments are usually yellow or red, sometimes the pollen also adds a bright yellow flush to the flower spikes. [ drawing web view or PDF to print ]
Each flower produces a small woody fruit containing hundreds of tiny seeds. These fruits form in clusters along the stem, and are usually held on the plant for many years. The seeds are usually not released from the fruits for several years, but in some species the fruits open after about a year. Fire also stimulates the opening of the fruits in some bottlebrushes.
The new leaves of many bottlebrushes are very ornamental. The leaves are often coloured and, in some species, they are covered with fine, soft hairs.

Bottlebrushes as Garden Plants

Bottlebrushes make excellent garden plants. Plants are all woody shrubs which range from 0.5 m to 4 m tall. The flowers can be spectacular and are irresistible to nectar-feeding birds and insects. Most species are frost tolerant.
The popularity of bottlebrushes as garden plants commenced soon after European settlement and Crimson Bottlebrush ( Callistemon citrinus ) was introduced to Britain by Joseph Banks in 1789.
Many species can tolerate (or thrive in) damp conditions, yet most are very hardy and will tolerate drought and limited maintenance. They grow well in a wide variety of soils, except those which are highly alkaline. Plants grown in full sun produce the best flowers.
Plants can be lightly pruned after flowering to keep them in shape. A low-phosphorous fertiliser should be applied in spring and autumn. Mulching will help retain soil moisture and reduce weed growth.
Many cultivars have been selected from natural variants and hybrids between species. Some of these are very good garden plants.


'Tip pruning' undertaken as new growth appears (bearing in mind that the next lot of flowers are formed on the end of this growth after it has hardened and therefore you may be sacrificing some flowers if you do not do this early enough), or

pruning just behind the flowers , as they are finishing, probably the preferred option unless prior to winter when subsequent new growth may be damaged by frost.


Commonly Grown Bottlebrushes

Callistemon brachyandrus - Prickly Bottlebrush

This prickly-leaved shrub grows best in well-drained soils in full sun and is an excellent plant for hot, dry areas. The tips of the small red flower-spikes are covered in yellow pollen and are most attractive. The rounded shrubs grow to about 3 m.

Callistemon citrinus - Crimson Bottlebrush

This hardy shrub is probably the best known bottlebrush and is widely cultivated. The bright red flower-spikes appear in summer and autumn. Crimson Bottlebrush grows well in wet conditions and usually reaches 4 m. Plants should be lightly pruned and fertilised after flowering. Neglected or mis-shapen plants respond to hard pruning.

Callistemon formosus - Kingaroy Bottlebrush

This attractive shrub is suitable for tropical and frost-free areas. Plants grow to 3 m tall and have weeping branches. Lemon-coloured flower spikes are produced throughout the year. It is planted as street tree in Kingaroy, Queensland.

Callistemon pallidus - Lemon Bottlebrush

A tough, frost tolerant species which grows well in most soil conditions. Plants grow and flower best in full sun. The lemon-coloured flower spikes are produced in summer. Plants grow to about 3 m.

Callistemon pityoides - Alpine Bottlebrush

This very hardy and attractive bottlebrush is available in several forms. The alpine form is especially attractive and grows as a compact bush to about 1 m tall. Other forms grow as erect shrubs to about 2 m. Yellow flower spikes are produced in spring and summer. Plants grow best in moist soils. Alpine Bottlebrush can withstand heavy pruning if required. It is frost hardy.

Callistemon salignus - Willow Bottlebrush

This small tree has attractive narrow foliage and white papery bark. It is drought resistant and quite hardy, although it can be affected by the frost in cold climates. The flower-spikes are generally white or greenish but pink, red and mauve forms can be found. An excellent garden and street tree which grows 5 to 12 m tall.

Callistemon subulatus

This compact shrub grows from 1 to 3 m tall and is able to tolerate quite wet conditions. Callistemon subulatus is a freely flowering plant which produces red flower spikes over summer. Light pruning after flowering will keep the shrub compact.

Callistemon viminalis - Weeping Bottlebrush

Callistemon cultivars

Callistemon 'Harkness' , Callistemon 'Hannah Ray' and Callistemon 'Dawson River Weeper' are large shrubs growing 4 to 5 m tall. All have an attractive weeping habit.

Callistemon 'Little John' is a dwarf cultivar which produces masses of flowers, and which has blue-green foliage.

Callistemon 'Reeve's Pink' and Callistemon 'Mauve Mist' produce attractive pink flowers and grow well near a wall in cold areas and flourish in warmer climates.

Frequently Asked Questions

When will a bottlebrush bloom in the northern hemisphere?

In areas where it can be planted outdoors, such as California, a bottlebrush might begin blooming as early as late December and bloom through late spring. These are the same months in which it will bloom in Australia, where it takes advantage of combined warmth and moisture during summer and fall.

What is the lowest tolerable temperature for a bottlebrush?

When planted in a sheltered area with plenty of direct sunlight, a bottlebrush is hardy down to 45 degrees Fahrenheit.

How much sunlight does a bottlebrush require?

Your bottlebrush plant is a sun lover. It likes six to eight hours of direct sunlight per day. Try to avoid planting it where it will be shaded a majority of the time.

Should I fertilize my bottlebrush in winter?

No. You should not fertilize your bottlebrush in winter. As for many plants, winter is a period of dormancy for your bottlebrush and it will not use the nutrients in the soil.

In which USDA growing zones will bottlebrush flourish outdoors?

Zones 8 through 11. These zones include states such as California, Florida, and Texas.

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