Buddleia davidii is one of around 140 recognized species in the Buddleia or buddleija genus and is the most well-known. Native to China and Japan, this is a widely grown ornamental plant.
This perennial, also commonly known as the butterfly bush, is grown for its abundance of long purple flowering racemes, and fast-growing habit. Butterfly bush shrub is one of the most cold-hardy buddleia species.
Unfortunately, despite its beautiful summer flowering display, it is considered invasive in many regions and can pose a threat to native species.
The buddleia genus hails from China and was introduced first into Europe in the late 1800s and, soon afterward, into America, Australasia, and parts of Africa.
|Scientific name||Buddleia Davidii or Buddleja Davidii|
|Common names||Summer lilac, buddleia, butterfly-bush, orange-eye|
|Height||6 – 7 feet (2 m)|
|Width||Up to 5 ½ feet (1.5 m)|
|USDA Plant Hardiness Zone||Zones 5 to 10|
|Native to||China, Japan|
|Flower colors||Shades of purple, lilac|
|Plant specific features||Considered invasive in many regions|
How to Plant and Grow a Butterfly Bush
Before planting Buddleia davidii, remember that it is a non-native shrub, fast-growing and spreads rapidly by wind-dispersed seeds. In many regions, it is considered invasive and a threat to native flora.
Where to Plant
Buddleia shrubs have naturalized around the world, and are often seen growing wild along rail tracks, roadsides, riverbanks, and on disused urban sites. In the United Kingdom after World War 2, the butterfly bush appeared on land destroyed by the bombing campaigns.
It became known as the bomb site flower for obvious reasons. Until this time, Buddleia davidii was known as B. variabilis due to its significant presence in the wild.
Choose a sunny location if you want the best results from your butterfly bush. You can also grow this perennial in a container.
If grown in a pot, make sure you provide a good drainage system to allow the roots to breathe and not sit in soggy, water-retaining soil.
A container-grown shrub will require regular watering, particularly in the summer months. Place the container somewhere where it will receive plenty of sun.
Select a deep and heavy container so that the plant will not topple over during windy weather. There are some dwarf cultivars of Buddleia davidii that are particularly well-suited to container growing.
One downside of container-grown buddleia is their cold hardiness. Whilst most varieties are frost-hardy when grown in garden soil, in pots the same is not true.
Unprotected during the winter, a buddleia is likely to die, so will need to move to a cold frame or unheated greenhouse.
When to Plant
Plant the shrub in the spring or the fall before the first frost. Like all shrubs, avoid planting during extreme climatic conditions, as this puts unnecessary stress on the plant.
Butterfly Shrub Care and Maintenance
Soil should ideally be fertile, and well-drained. Whether grown in garden soil or in a container, good drainage is essential. Without this, the plant’s roots will rot, and the shrub will die.
Butterfly bush is not a fussy shrub when it comes to soil type. If the soil is very heavy, water-retaining, or clay, then it is a good idea to use a soil conditioner before planting. Add some grit if it is very wet, and enrich poor soil with some organic compost.
With regard to pH levels in the soil, a buddleia prefers the soil to be slightly alkaline. This is why they tend to be successful at roadside edges and on disused building land. If your soil is acidic, you can add some limestone chippings to the soil; this will also aid with drainage.
Immediately after planting, make sure you give the butterfly bush a good soaking. For the first growing season, make sure it doesn’t dry out, as it will be developing a robust root system at this stage. But once it is established, cut down on the watering.
Subsequently, during the early part of the growing season, water is only during dry weather. In the summer, when the plant is flowering, avoid over-watering as this will encourage foliage rather than flowers. A buddleia is considered to be a fairly drought-tolerant plant once it is mature.
In the spring, after you have cut back your shrub, apply a top dressing of general purpose, slow-release fertilizer. Preferably use a product that is high in potassium as this will result in better flower production.
Never use a fertilizer that is high in nitrogen, as this will encourage leaf growth at the expense of flower production.
Buddleia shrubs don’t need much feeding, in order to survive. But you will notice much improved blooming with additional nutrition, providing you don’t’ over-feed.
Plant the buddleia in a spot where it is going to get a lot of sunlight. If possible, plant in full sun, where the shrub will get over six hours of sunshine.
Although they will grow in some shade, more butterflies and bees will be attracted to the buddleia if it is in a sunny location.
Pruning and Repotting
Pruning buddleia is best carried out twice a year. In the early spring, cut the main branches back to about 10 inches (25 cm) from the ground. Only leave about four or five main growing branches.
At the same time as this first pruning, check the plant for any diseased, damaged or dead wood which should also be cut off and removed. Make sure you use clean tools so that you won’t introduce disease into your shrub.
Deadheading the buddleia isn’t essential for the plant’s health or for its flowering potential. However, it is important to cut down on the risk of the plant developing seeds. So, as blooms finish, cut them off and remove them.
Once the plant has finished flowering in the fall, cut off all the rest of the remaining dead flowers. This is done to reduce the chance of the buddleia self-seeding.
Butterfly bush is a plant that is considered an invasive species. As a responsible gardener, you should do all you can to prevent its seeds from forming or dispersing into surrounding land and germinating outside your garden.
Pruning the butterfly bush effectively is the best way to keep the desired shape and size of the shrub. It also encourages new growth and more flowers for the following season.
Before propagating buddleia, remember the plant’s status in many regions as an invasive species, or weed.
Buddleia produces a lot of seeds, and if they are left on the shrub, they will be dispersed into the surrounding land by wind and birds.
Seeds will germinate easily, and often you will see seedlings popping up around the base of your buddleia. However, if you try to propagate them from seed, you have to provide a period of cold stratification before they will germinate.
And they can take up to four months to germinate, so it is not the quickest or easiest method to choose.
If you wish to propagate your buddleia, and haven’t allowed the flower heads to set seed, you can take stem cuttings. They will root easily and quickly. In the spring or the summer, you can take stem cuttings.
The pieces of the stem should be taken from new growth and about 3 inches (7.62 cm) long. The use of a hormone rooting powder will speed up the rooting process.
Removing the lower leaves will help the cutting root easier, and you should use good quality potting compost. Keep the cuttings warm and damp, and they should start to form small roots within a few weeks.
Another easy way in which you can propagate your butterfly bush is by root division. If you wish, you can dig up the butterfly bush and tease the roots apart.
Either do this by hand, or by carefully using a garden spade. You can plant the divided pieces directly in the ground, or plant them up into containers. Root division can be carried out either in the spring or the fall.
Pests and diseases
This relatively easy-to-grow plant is not usually severely troubled by pests and diseases. This is one of the reasons it does so well in the wild and has become a species considered a threat to native flora and fauna.
Ensuring the well-being of your plant is key to preventing the onset of pests and diseases.
Maintaining good air circulation around the plant’s foliage and stems will help to prevent diseases such as downy mildew or root rot. Equally critical is the drainage of the soil.
It is essential that the butterfly bush is not left to sit in water-logged soil for extended periods of time. However, the more mature the shrub, the better it will be able to tolerate less than optimal growing conditions.
Fungal diseases such as mildew and root rot are observed by yellowing of the leaves. The roots will rot, and if left untreated, the plant will die.
This is often caused by long spells of cold, damp, or wet weather. Although it is difficult to get rid of the fungal spores, treatment with a soil fungicide can help. This treatment usually needs to be repeated on a regular basis.
Temperature and Humidity
Although this shrub grows wild in China and Japan and is considered hardy in USDA zones 5 to 10, it is a very tolerant plant. It is tolerant of both winter cold and summer heat.
In colder regions, it will die back to the ground level each winter. In the spring, it will re-sprout from the base, and be completely unaffected by its winter die-back.
Conversely, in hotter climates, the buddleia will be semi-evergreen. Because it doesn’t die back each winter, it has the potential to grow into a much larger shrub or tree. If hot temperatures continue over 90° F, then the shrub will stop producing flower buds.
However, more flowers should arrive once the temperatures start to fall. This means that the flowering season can continue well into the fall in hotter climates.
Other Uses for Buddleia Davidii
Buddleia bushes are resistant to deer and attract butterflies, which feed on the nectar contained in the flowers.
In China, the butterfly bush is called the skin-care plant. Both the flower buds and leaf extracts are used in Chinese medicine.
Types of Buddleia Davidii You Can Grow
There are several cultivars of Buddleia davidii, including ones that are sterile. This factor eliminates their ability to reproduce viable seeds for dispersal into the wild.
These cultivars can be distinguished by their flower shape, foliage form, size, and color.
Buddleia davidii “Adonis Blue” is a dwarf variety that will not exceed 5 feet (1.52 meters) in either width or height even when the shrub reaches maturity.
Buddleia davidii “Black Knight” flowers profusely and produces deep purple, fragrant blooms mid and late summer.
Some species and cultivars can also produce white flowers, such as Buddleia davidii “Buzz ivory”. The flowers of this cultivar are sweet smelling and the plant won’t grow more than 5 feet tall.
However, the majority of these plants bear a shade of purple, violet, lilac, or blue panicles.
Buddleia davidii var. magnifica has lilac flower spikes that can be 24 inches,(60 cm) in length.
Buddleia shrubs are unpopular with local authorities due to their ability to thrive and spread on wasteland, railway track sides, and in the mortar of walls of buildings.
However, their bad reputation is not always justified. Too often, it is caused by the neglect of the corporate bodies that allows the shrubs to grow out of control.
Many other garden plants that are considered invasive do far greater damage to their surroundings than the butterfly bush.
Butterfly bush shrubs offer a brilliant floral display in the summer garden, and are a low-maintenance, easy-to-care-for shrub that can be kept at any desired size.
Responsible gardeners however may prefer to steer clear of this plant and consider growing a native species instead such as a variety of Ceanothus thyrsiflorus (blue blossom).
*image by katerynka/depositphotos