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Bottlebrush Tree - Tips on Growing and Caring For Callistemons

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by Max - last update on May 7, 2019, 8:07 pm
Bottlebrush Tree

The bottlebrush tree, despite its name, is actually a shrub. It is most often grown as a large shrub or shaped into a small tree with particular pruning. The common name of bottlebrush refers to the plant’s blooms, which are a spiked flower sitting at the very end of a stem, looking remarkably like a brush used to clean bottles or jars. They can be quite large, reaching up to 12 inches long in some species. Made up of many individual blossoms, these flowers are typically produced in various shades of red, and are a good way to attract hummingbirds, butterflies, and other wildlife.

Quick Facts

OriginAustralia
Scientific NameCallistemon
FamilyMyrtaceae
TypeEvergreen shrub
Common NamesBottlebrush tree, crimson bottlebrush, red bottlebrush, green bottlebrush, yellow bottlebrush, bottlebrush plant, bottlebrush shrub, weeping bottlebrush
Ideal Temperature50- 90° F
LightFull sun
WateringModerate
HumidityModerate

Caring for Your Bottlebrush Tree

Callistemon bottlebrush care

Watering

This plant should be moderately watered when it is young, though it will become drought-tolerant once it is established (Australian National Botanic Gardens). In spring and summer, you should water the plant once a week if it hasn’t recently rained, showering the plant slowly to give the water a chance to be full absorbed deep into the soil.

Layering mulch over the soil will help with water-retention, reducing the amount of water that evaporates, leaving the soil in a more moist condition. As with any plant, be careful not to over water in order to prevent root rot. Root rot is usually fatal for bottlebrush trees and cannot be remedied. Your best protection against root rot is prevention, ensuring you don’t provide the plant with more water than it needs. This is especially important if you grow your bottlebrush tree in a container, as the soil will hold onto the water due to it having less opportunity to drain than ground soil.

This plant is not especially fussy when it comes to soil and will happily grow in any type of well-draining soil. You can always add builders sand to your soil mix to help it drain better and reduce the chances of root rot occurring.

Temperature

As a native of Australia, this plant likes to be kept warm. In mild climates, it can live all year round, though if you live in an environment where winters are cold, then you will need to grow the bottlebrush tree in a container so that it can be moved inside during chilly months.

Light

bottlebrush callistemon shrub blooming outside
The bottlebrush tree thrives in full sun and needs plenty of direct sunlight to produce the striking brush-like flowers

The bottlebrush tree thrives in full sun and needs plenty of direct sunlight to produce the striking brush-like flowers. If you are planting this tree directly into the ground in your garden, ensure it is in an area that will get at least six hours of sun a day. Watch out for neighboring plants which might grow bigger than the bottlebrush tree, resulting in it being put in the shade by the bigger plant.

For encroaching plants, cut them back to enable the bottlebrush tree to have full access to daylight, or dig up your bottlebrush tree and replant it in a more suitable location. Bottlebrush trees in containers will need to be positioned in a sunny spot and can be moved around if necessary to give them the best chance of good health and flower production.

Pruning

The bottlebrush tree only requires a light pruning. The time of year you prune this plant will directly affect its ability to flower, with continual pruning often leading to a lack of blooms the following year. The basic rules are that pruning for size or shape should be done in early spring while pruning for health and maintenance should be done in both early spring and late summer.

Bottlebrush trees can typically grow to around 15 feet in height, but if this isn’t ideal for your space, then you can trim it back each year and maintain an appropriate height. If aggressively pruned each year, you can keep the bottlebrush tree at a very compact size in an 8-inch sized pot. Although the plant is actually a shrub, some people like to prune it into the style of a tree, with long stems in place of the trunk, and an umbrella-shaped upper section forming the leafy part of the tree. This sort of pruning should take place annually in early spring before any flower buds form, as this will prevent interference with flower production.

To prune back the plant, whether it be to shape it specifically or to cut back its size, you should make your cuts on each branch just above a node. Bottlebrush trees, when done correctly, respond well to pruning. As with most shrubs, a light pruning of the stems diverts the plant's energy into flower production, so cutting your plant back will be beneficial if you enjoy the bottlebrush tree in bloom.

Pruning for the plant's health should be addressed twice a year, both in early spring and late summer. If flowers are still in bloom, you should delay pruning the plant, only going ahead once flowers have faded to prevent problems with growth in the future. Cut back any dead or damaged stems, and look for any inner stems which have gone brown. Brown stems on the interior of the plant are a result of lack of sunlight. To resolve this problem, you should lightly thin out the plant to enable the sun to reach more of the inner branches.

Feeding

This plant will benefit from a monthly feeding during warmer months of a fertilizer high in phosphorus. This will help the plant to produce an abundance of flowers. If you find your bottlebrush tree is struggling with flower production despite you getting all of the caring conditions seemingly just right, it could be down to using the wrong fertilizer.

Different nutrients in fertilizer have different uses. Phosphorus aids in flower development, while nitrogen encourages foliage growth. If you use a fertilizer that has a high percentage of nitrogen, then your plant will become very leafy, and this is often at the detriment to flower production. Ensure your fertilizer is either a general-purpose fertilizer with equal parts of the three main plant nutrients or one that has a higher proportion of phosphorus.

The method you use to fertilize the bottlebrush tree is personal preference and will not affect the health of the plant, providing you follow the instructions on the packaging. Many people opt for granular fertilizers for outdoor plants growing directly in the soil, while liquid fertilizer is better suited to container plants.

The bottlebrush tree is susceptible to fertilizer burn, which can cause leaf discoloration, so if you are new to using fertilizer or are unsure of the amounts to use, err on the side of caution and use less than you think necessary. A lack of fertilizer will cause less damage than using too much.

Do not fertilize this plant in the colder months as it will not be growing and therefore not need the extra nutrients.

Propagation

If you want to propagate your bottlebrush tree, you can do so from seeds or from stem cuttings (Royal Horticultural Society). Both options are easy and very rewarding to do.

To collect seeds from your bottlebrush, you will need to locate the woody fruit produced by each blossom on the plant. You will be able to find these small fruits growing along the flower stems in clusters. Remove them from your plant, unopened, and store them in a cool, dry place inside a paper bag. Then, wait for the fruits to open, revealing hundreds of tiny seeds from each fruit. Sow the seeds during spring in moist soil and wait for seedlings to appear, transferring them to slightly larger pots when mature enough and continuing care as usual for young shrubs.

Due to the common cross-pollination of bottlebrush trees, growing the plant from seed does not guarantee that the new plant will be the same variety as the mother plant. If you are keen to ensure your new plants are a direct copy of the parent plant, you will need to propagate using stem cuttings instead of seeds.

Propagation by stem cuttings can be done during summer with semi-mature woody stems. Make your cut with clean shears at a 45-degree angle to create the most surface area from which roots can form. Your cutting will need to be around six inches in length, with all of the lower leaves removed. Any flowers or flower buds will also need to be snipped from the cutting. You can dip the raw end of the cutting in rooting hormone to encourage roots to form and increase your chances of successful propagation, but it isn’t entirely essential and can be skipped if you wish.

Stand the cutting in either a jar half filled with water or in a small pot filled with soil, ensuring that the soil is packed tightly enough around the stem to prevent it from falling over. If you are using soil to propagate your stem, keep it moist but not wet, and, ideally, cover it with a plastic bag to help increase humidity.

If you are using water to propagate your stem, change it at least every other day to keep it fresh. Place the stem cuttings in a warm place, ideally with bottom heat, and no direct sunlight. In eight to twelve weeks, your stems should have rooted. If you are propagating in water, then the development of stems is easy to witness.

If the stems are in the soil, you can check to see if roots have formed by gently tugging on the stem and seeing if it offers any resistance. Stems which will easily be pulled from the soil do not have any roots, while those that hold onto the soil are showing evidence of root development. Once roots are present, you can remove the plastic covering and move the pot outside to a warm and sunny spot. Ensure the young plant is well-protected from strong winds and continue care as normal, either planting directly into the ground or into a bigger pot when the plant is strong enough.

Disease

The bottlebrush tree, in general, is quite a robust and healthy shrub, but there are some diseases that can strike the plant and cause lasting damage if not correctly treated. The most common diseases affecting the bottlebrush tree are listed below.

Powdery Mildew

Powdery Mildew

This is a disease that commonly occurs in moist or damp conditions. It presents itself as a powdery white or gray covering on the plant and can appear anywhere from leaves, stems, flowers, and fruits. In severe cases, it will turn the leaves brown or yellow.

If your bottlebrush tree suffers from powdery mildew, you will need to treat it with a fungicide. The best defense against powdery mildew is prevention. Try to plant your bottlebrush tree in a bright and sunny spot away from dark and damp corners where mildew thrives. Moisture on the surface of the leaves will help mildew to develop, so try to keep the foliage dry by watering the plant from underneath. If you use sprinklers to water your plants, do so during the morning so that the sun has a chance to dry the leaves off during the day, instead of using sprinklers in the late evening.

Twig Gall

Twig Gall

This plant problem is a direct result of overly wet soil. If you notice that your bottlebrush tree has branches and stems which are bloated in appearance, and your soil is constantly wet, then your plant is most likely suffering from twig gall. This is a fungal disease that can be fatal if left untreated but is easy to treat with high levels of recovery when spotted in good time. Simply remove any diseased branches from your bottlebrush tree and dispose of them. Sort out your wet soil problem by correcting your watering schedule, watering the plant with less frequency and with less water. Consider adding sand to the soil and mixing it in to aid with better drainage.

Verticillium Wilt

Verticillium Wilt infection wilting

This difficult-to-diagnose disease is caused by a fungus that lives in the soil. It enters the plant from the roots and travels up the plant's vascular system, leaving a trail of curled and yellow or brown leaves as it goes. Plants suffering from verticillium wilt also experience leaf loss and branches which die back.

Due to the fact that many other diseases or pest infestations can present in similar ways, it’s hard to diagnose verticillium wilt. One way to identify it is to slice through a stem or branch on your suspected plant. If you see dark rings of color on the cross-section, then this is a good indication that your plant has verticillium wilt. The dark circles are made by the fungal disease as it travels throughout the plant.

If your bottlebrush tree is suffering from verticillium wilt, then you have two options. You can remove and dispose of the plant, or you can try to build up the plants resistance against the disease. The fungus will remain in the soil and is hard to get rid of. If you choose to dispose of your plant, be sure not to replant anything that is susceptible to verticillium wilt in the same area. If you want to try to save the plant, prune off any infected branches and try to improve the health of the plant so that it is strong enough to fight off the disease. Use monthly fertilizer and ensure the plant has adequate water and sunlight.

Root Rot

This disease is more common in houseplants, but it can affect plants living outside as well. It is directly caused by the soil being too wet, in which a fungus develops. The fungus attacks the roots and leaves the roots unable to absorb moisture or nutrients that the plant needs, which will result in a plant that looks as though it has been suffering from drought, even though the opposite is actually the case. Plants suffering from root rot will have yellow or browning foliage, stunted growth, leaf loss, and branches that die back.

Root rot is one of the most common problems affecting plants and trees, and it is also one of the most fatal. If your bottlebrush tree has root rot, it will be difficult to save it unless you have noticed it in the very early stages. For root rot, prevention is much better than a cure. You should ensure your soil drains well, adding sand or organic matter to your soil to improve any drainage issues. Take note of your plant’s watering requirements and don’t water too frequently or too heavily. Your bottlebrush plant will much prefer to live through occasional periods of drought than continuously wet soil.

Do you have any questions about Bottlebrush trees? Let us know in the comments. And share this page with others who might be interested in this type of plant!

Bottlebrush Tree - Tips On Growing And Caring For Callistemons

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