Introduction to the Butterfly Bushes (Buddleias)
Buddleias are wonderful woody shrubs with large, fragrant, colorful flowers that attract a flutter of butterflies into your summer garden. Buddleias are extremely easy to grow and any novice gardener will have success with this genus. Buddleia breeders are hard at work creating marvelous new cultivars with novel flower colors, flower shapes, leaf colors, and dwarf habits. If you are still growing some of the older cultivars, you will be amazed how far they have come in recent years.
Buddleia History and Background
The common names for buddleia are butterfly bush and summer lilac. Butterfly bush should not be confused with the common herbaceous perennial butterfly weed, Asclepias tuberosa (a plant smoked by delinquent Lepidoptera). The first species of buddleia known to science was tropical, the Central American Buddleia americana which made its way to Europe from the Caribbean Islands in the 1730s. The buddleia that we commonly grow today, Buddleia davidii, was not discovered and brought into gardens until the 1890s.
The hundred or so wild buddleia species have a worldwide distribution between 40N to 40S latitude. Buddleias are divided into two groups, the new world buddleias, which are native from the southeastern United States to Chile, and the old world buddleias which are native to Africa and Asia.
The commonly grown Buddleia davidii is native from central China to Tibet at elevations up to 7800′ (2600m) and is one of the most cold hardy buddleia species. There is a large species diversity of buddleia in Asia and the Americas, but the highest is in South Africa which leads scientists to speculate that they originally evolved there. Some species have a very wide natural range (Buddleia americana, Buddleia asiatica, Buddleia crispa) while others are rare and exist only in a small region (Buddleia coriacea, Buddleia utahensis). Most buddleias are woody shrubs from 6′ to 16′ in height. Others are 40-80′ tall trees (e.g., Buddleia cordata, Buddleia limitanea, Buddleia saligna), some are dwarf shrubs less than 3′ tall (e.g., Buddleia pterocaulis, Buddleia utahensis), some are woody vines (e.g., Buddleia madagascariensis), and at the northern edge of their geographic range some are herbaceous perennials. Buddleia davidii is a widely grown ornamental plant in temperate areas around the world. Dozens of cultivars have been released covering a wide range of flower color, leaf color, and plant size. It is a very successful ornamental crop for landscape use, container gardening, and cut flowers. In the United States, buddleias are grown mainly in USDA hardiness zones 5-10, and are herbaceous perennials in the Zone 5 end of the range.
Outside of the garden, buddleias have only a few economic uses. Some cultures extract dyes or essential oils from the stems or the flowers. Others use extractions from the leaves to treat headaches, burns, wounds, or ulcers. Some species produce important secondary metabolites such as flavinoids, terpenoids, iridoids, or phenylethanoids that may have economic value. The Chinese mix Buddleia lindleyana leaves with coal and throw them into waterways to intoxicate fish who then float to the surface and are easier to harvest. It must be something in the buddleia leaves since most rivers in China are already full of coal and petroleum products.
The native Chinese species, Buddleia davidii, has a reputation for being weedy in some places. Buddleias are pioneer successionary species: each plant produces millions of seeds and a plant can grow from seed to a mature flowering adult in a single year. The seeds have tiny wings on them and can float a long distance on the wind. Buddleia davidii plants will colonize any piece of bare soil in sunny locations such as roadsides, riparian areas, pastures, and other disturbed areas. After World War II, many of England’s bombed-out home sites had buddleias growing on them. Even today, the English countryside is painted with buddleia flowers every summer. Buddleias do not like direct competition from trees or other tall plants, and therefore will die out in area with a climax forest successionary regime.
Buddleia davidii is considered to be an invasive weed in New Zealand, England, France, Oregon and Washington state. Similarly, Australia, Fiji, and Hawaii consider it to be potentially invasive and maintain a careful watch. Buddleia davidii has naturalized in England, as well as many US states such as California, Pennsylvania, North Carolina, Virginia, Delaware, Maryland, New Jersey, Kentucky, and West Virginia but is not considered invasive or harmful.
For gardeners whose property borders a non-forested natural area, use the sterile or low fertility cultivars or remove the seed heads in the fall before they open. Many of the modern cultivars of Buddleia davidii have dramatically reduced fertility and are not invasive. Some hybrid cultivars (such as ‘Blue Chip’) are almost completely sterile and pose no threat. Some low viability selections include Buddleia weyeriana, Buddleia fallowiana, Buddleia hemsleyana, Buddleia longifolia, Buddleia macrostachya, and Buddleia nivea.
Buddleia Morphology
Buddleia leaves are lance-shaped (lanceolate) and are arranged oppositely along the branch (except Buddleia alternifolia). The leaves range in size from ” to 11″ long (1 to 30cm). Some species are deciduous, some are semi-evergreen, and some are evergreen. The common Buddleia davidii is semi-deciduous in North Carolina. Many butterfly bush leaves have small white hairs on their surface and some cultivars such as Buddleia marrubifolia are hirsute enough to give the leaf an attractive silvery-grey appearance. The hairy cultivars are also more resistant to spider mites and the hairs also reduce water loss which make the plants more drought tolerant.
Buddleia “flowers” are actually inflorescences; a collection of many small “florets” on a single floral structure. Each inflorescence consists of dozens of small tubular florets that are 0.5″ long and 0.1″ wide (1cm by 3mm) each with 4 spreading petals.
Most common garden varieties of buddleia are old world species and the inflorescence is a cone-shaped panicle. However, new world buddleia species tend to have spherical inflorescences called globose cymes or racemes. The inflorescences may occur at the tips of the stems, or along the length of the stem. In some species, the inflorescences span dozens of nodes on the stem and have small bracts or leaves between them. Buddleia panicles are from 4 to 20″ long (10 to 50cm) and cymes may be from 2-5″ across depending on species.
Buddleia davidii, Buddleia fallowiana, Buddleia officinalis, Buddleia paniculata and Buddleia salviifolia have erect panicles at the tips of the branches. Buddleia asiatica, Buddleia colvilei, and Buddleia lindleyana have panicles that are long enough to arch over or cascade downward from the branches. The cymes and racemes of new world species may form at every node on a long cascading branch (Buddleia alternifolia) or an erect branch (Buddleia globosa, Buddleia utahensis). Cymes and racemes of new world species may also form at the tip of a branch (Buddleia crispa, Buddleia saligna).
Flower color may be white, purple, blue, pink, yellow, orange, or a reddish-purple color that buddleia marketers like to call “red”. Buddleia davidii and most of the other old world species have separate male and female florets on the same plant (monoecious). New world species tend to have separate male and female plants (dioecious). There are also perfect-flowered species (hermaphrodites). Plants are self-fertile and members of the genus easily cross with each other to form interspecific hybrids with intermediate floral traits.
Common garden butterfly bushes (Buddleia davidii, Buddleia lindleyana, Buddleia fallowiana) have flowers with a sweet honey fragrance that is strongest at midday. The agreeable scent attracts a variety of butterflies, insects, birds and of course, gardeners. A few wild species have little scent, or a fetidly sweet scent that some people find disagreeable. Buddleia salviifolia is said to have the best fragrance of all, smelling like Chanel perfume.
The common garden species are long-day plants and flower in the summer. Flowering starts in July and lasts until first frost, but most of the buddleia hybrids produce their best floral show in early summer. In hot summer climates with warm nights, the summer produced inflorescences will often be dramatically smaller, returning to their full size only when fall approaches and the night temperatures cool.
Some of the other buddleia species are short-day plants such as Buddleia alternifolia which blooms in early spring. Both Buddleia asiatica and Buddleia officinalis bloom in late winter. Interestingly, the natural diploid species are usually short-day plants and the natural tetraploid species are usually long day plants.
The sweetly scented buddleia flowers attract many types of butterflies and at times, the flowers will be covered with hundreds of them. Buddleias act as both nectaring and food plants to many butterflies, including some that normally feed on other plants. Buddleias are host plants to the North American butterfly species listed below:
* American Snout
* Anise Swallowtail
* Black Swallowtail
* Cariable Checkerspot
* Common Buckeye
* Common Checkered-Skipper
* Eastern Comma
* Eastern Tiger Swallowtail
* Echo Blue
* Giant Swallowtail
* Great Spangled Fritillary
* Monarch
* Mourning Cloak
* Painted Lady
* Peacock
* Pearl Crescent
* Pipevine Swallowtail
* Polydamus Swallowtail
* Red Admiral (prefer white blossoms)
* Spicebush Swallowtail
* Tortoiseshell
* Two-tailed Tiger Swallowtail
* Western Checkerspot
* Western Tiger Swallowtail
* Zebra Swallowtail
Bees, wasps, hornets, lady beetles, lacewings and moths also enjoy the flowers. Hummingbirds are attracted by the reddish cultivars. Other birds such as orioles and bushtits will feed on the nectar during the growing season and on the seeds in winter.
The fruit is usually a two-valved capsule that splits at maturity to release about 50 seeds. Some species (e.g., Buddleia axillaris, Buddleia japonica) produce berries instead of capsules. The seeds are generally not released until late December and they release gradually over several months.
Buddleia Taxonomy
An alternate spelling for buddleia is “buddleja”, and like a good mystery novel, the nomenclatural plot thickens. Reportedly, British surgeon and botanist Dr. William Houstoun (1695-1733), in his Catalogus plantarum Horti regii parisiensis, first spelled the name “buddleia”. Carl Linnaeus then reportedly misspelled it in the taxonomic bible, Species Plantarum as both “buddleja” in the text and “budleja” in the index. In a later edition of Houstoun’s work, published by Sir Joseph Banks in 1781, three different spellings can be found: buddleja, buddleia, and buddlea. Many taxonomists also consider the name buddleja to have been misspelled, because according to the rules of Latin; the suffix “ja” is grammatically incorrect and the suffix “ia” is the proper way to create a genus from the name Buddle. Nowadays, most European taxonomists use the spelling buddleja, but almost everyone else uses the orthographical variant spelling buddleia…and we will follow the latter convention in this essay. In recent years major references from the American Horticultural Society, and the Royal Horticultural Society have been reverting from buddleia to buddleja. Many Americans rely on a reference book called Hortus Third which uses the term buddleia.
The name buddleia commemorates the amateur botanist and bryophyte expert, Reverend Adam Buddle (1662-1715). Buddleia was named for Buddle posthumously to recognize him for writing an early Flora of the British Islands. Oddly enough, Reverend Buddle never grew a butterfly bush. The first known butterfly bush species, Buddleia americana, wasn’t sent to European botanists until 1730, after Buddle’s death. The commonly grown Buddleia davidii, was named for French Jesuit missionary and naturalist, Pre Armand David, who first discovered it.
The genus Buddleia has been tossed about between taxonomic families. Buddleia was originally assigned to the family Scrophulariaceae by taxonomist Antoine Laurent de Jussieu in 1789, but in 1856 Taxonomist George Bentham moved it to the family Loganiaceae. In 1975 it was moved to its own family, Buddlejaceae, where it has stayed until very recently. Recent DNA analysis and phylogenetic studies have generated cladograms that place the entire family Buddlejaceae inside of the family Scrophulariaceae. The family Scrophulariaceae is complex and is considered to be a catch-all family for undefined genera in order Lamiales. However, this story is not over yet, work is still ongoing to sort it all out.
The genus Buddleia has over 100 species in it, but only a handful are used in ornamental gardens. These include Buddleia alternifolia, Buddleia asiatica, Buddleia colvilei, Buddleia crispa, Buddleia fallowiana, Buddleia globosa, Buddleia lindleyana, Buddleia marrubifolia, Buddleia officinalis, Buddleia paniculata, Buddleia saligna, Buddleia salviifolia, and the ubiquitous Buddleia davidii from which most of the common garden cultivars arise. A hybrid of the otherwise unused species, Buddleia stachyoides and Buddleia tubiflora also has garden merit. The man made interspecific hybrid Buddleia globosa x Buddleia davidii has been given the unique epithet Buddleia x weyeriana. This cross was originally made by the first buddleia breeder, Mr. Van de Weyer in Dorset, England in the early 20th century.
Buddleia Genetics & Breeding
Modern breeding of buddleias began in 1900. Naturalist E.H. Wilson made germplasm collections of Buddleia davidii from western China while traveling for the Veitch Nursery in London and the Arnold Arboretum. The material sent to this plant nursery formed the basis of the modern garden hybrids. Buddleia x weyeriana created in 1914 by Mr. Van de Weyer is still popular today.
New cultivars are being announced every year by breeders and plant nurseries. The new cultivars offer novel combinations of plant height, leaf color, and flower color. Flower colors vary along a continuum and include hues of white, blue, purple, pink, orange, and yellow. A few cultivars even have flowers with branched panicles. Newer cultivars tend to be sterile or have vastly reduced seed germination and are thus less likely to seed around. Since sterile hybrids do not expend energy producing seed, they are usually very floriferous. Garden cultivars exist at every possible plant height from 2′ to 15′ and breeders are focused on releasing dwarf selections or more tightly branched selections that can fit into smaller gardens. Other breeders focus on leaf characteristics such as leaf color, variegation, and hirsuteness.
Buddleia breeders sometimes select plants for polyploidy (more than 2 sets of chromosomes) because some polyploids are sterile. Up to 40% of the buddleia species are natural polyploids. Buddleias have a chromosome number of n=19 (that is, there are 19 chromosomes in each set). There are also buddleias that are natural tetraploids (4n)(e.g., Buddleia davidii). Triploid buddleias also exist and are sterile. Asian species tend to be polyploid and new world species tend to be diploid. It is hypothesized that buddleias are allopolyploids that arose from a intergeneric cross between Gomphostigma (2n=14) with Retzia or Nuxia (2n=24).
Five of the most prominent modern buddleia breeders and programs are:
Dr. Dennis Werner of North Carolina State University has a decade long buddleia breeding program that focuses on novel leaf color, novel flower color, and dwarf habit. Werner makes controlled crosses using Buddleia davidii, Buddleia globosa, Buddleia lindleyana, Buddleia davidii var. nanhoensis, and Buddleia fallowiana. He is currently screening for sterility, true red flower color, and better yellows and oranges. His two recent releases, Buddleia ‘Blue Chip’ and Buddleia ‘Miss Ruby’, have won many accolades. In particular, Buddleia ‘Blue Chip’ is a breakthrough in breeding for its extremely dwarf habit. As it is nearly sterile it does not pose any “flight risk” like older cultivars. He is using Buddleia ‘Blue Chip’ and another dwarf, Buddleia ‘White Ball’ as parents for new hybrids. Dr. Werner has also directed graduate students in the study of genetic mechanisms of flowering in buddleia and is experimenting with using radiation to induce mutations. This research may someday help create better flowering cultivars. In the future, look for new exciting cultivars to come out of this breeding program.
Dr. Jon Lindstrom of the University of Arkansas has a two decade long buddleia breeding program with a three-pronged approach. One goal is to release sterile hybrids that produce little or no seed. A second goal is to create silvery foliaged plants (like Buddleia ‘Lochinch’) with a wide range of flower colors. His third goal is to use uncommon buddleia species that bring novel traits into garden cultivars.
There are a number of new cultivars entering the market from breeder Peter Podaras, currently at Cornell University. Peter has created some dwarf cultivars and has used some lesser known buddleia species in his crosses. His first plants are entering the market in 2010.
Dr. Mike Dirr [retired] of the University of Georgia ran a buddleia evaluation program that focused on attractive garden hybrids and spider mite resistance. His program released the popular hybrid cultivar Buddleia ‘Honeycomb’ which is considered to be the best yellow-flowered cultivar. He also released the unique Buddleia ‘Bicolor’ with its two-toned flowers.
The Boskoop Agricultural Research Station in the Netherlands selected and released several excellent cultivars including the compact Buddleia ‘White Ball’ and Buddleia ‘Pink Delight’. Elizabeth Keep of East Malling Research Station in Kent England has bred many cultivars of buddleia with the goal of refining the habit to make bushier plants that are smaller in stature.
Buddleia Culture
Buddleias should be planted in full sun to ensure the best growth habit and the largest number of flowers. Most buddleias are tall and need to be placed at the back of a bed, but as we mentioned, there are some dwarf buddleias that will look good at the front of the border or as edging plants. Buddleias should be sited near a window, along a path, or close to a patio or porch where you can smell the wonderfully fragrant blossoms during the summer months. In addition, they are quite tolerant of urban pollution which makes them well-suited to city landscapes and roadside plantings.
Buddleia davidii is cold hardy to zone 5 which makes it suitable for most gardeners in the United States. However, hybrids that have been bred with other buddleia species may be less cold tolerant as some of the other wild species are only hardy to zone 7 or 8. Near the edge of their hardiness range, they will die back to the ground in the winter and act more like herbaceous perennials. Buddleias are tough plants that can tolerate lean and even alkaline soils. They look best in a well drained average garden soil with a pH of 5.5 to 7.0 but can tolerate an alkaline pH up to 8.5. Buddleias do not like poorly drained soils and will rot. Clay soils are best when amended with organic material or when the bed is raised up above the surrounding grade. Buddleias are not heavy feeders, so a good, nutritionally balanced soil with adequate organic amendments is fine.
Buddleias are drought tolerant and can be grown without much supplemental watering once established. During extended periods of dry weather they should receive a thorough watering once every couple of weeks. Container grown plants will need more regular watering, typically once per day. Allowing a buddleia to become drought stressed will result in a much greater chance of insect infestations, such as spider mites.
Pruning Buddleia
Large buddleia hybrids will benefit from yearly pruning as they are weak-wooded and tend to split with age. Many of the commonly grown buddleia hybrids grow too large for the number of roots they produce. If they are not pruned annually, they will often blow over in the wind. Also, most of the Buddleia davidii cultivars flower on new wood and therefore can be cut hard in late winter. We generally cut them back to 2′ tall, but many can be cut to the ground and will recover. Buddleias should not, however, be cut hard in the fall as the loss of insulating branches and stored sugars may reduce their winter hardiness. If seed production and dispersal is a concern on fertile buddleias, gardeners should remove the seed heads in October. The seed heads will not open up until November or December.
While hybrids need pruning, there is little need to prune species buddleias, which are well adapted to their root system and will not fall over like the large hybrids. A few of the species, such as Buddleia alternifolia actually flower on old wood. Pruning on the species should be limited to minor shaping if needed.
Propagation
Buddleias may be propagated by stem cuttings or by seed, with cuttings being the only option to reproduce named clones. Cuttings may be taken from softwood in May, half-hardened wood in July or from mature wood in October. Short, side shoots with many nodes work the best. Treat the cuttings with rooting hormone (1000-3000 IBA) and place them under mist. The tiny buddleia seeds should be collected from November to February when they are normally released. The seed require a short cold stratification period of only 4 weeks. They will germinate in 3-4 weeks if surface sown under light at 70F to 80F. Grow the seedlings until they have 2 or 3 leaves but take care to avoid damping off by providing air circulation and watering carefully. Harden off the seedlings by moving them outside after the last frost to a protected location and gradually increase the light level and moderate the temperature until they are growing in full sun at outside temperatures.
Pests and Diseases of Buddleia
Buddleias are generally free of pests and diseases in the garden. When the plants are stressed they may be attacked by spider mites. Less frequently Japanese beetles, caterpillars, weevils, or mullein moth may feed on the plants. Scale has also been reported on stressed plants in some states. Spider mites can be controlled with a commercial miticide or oil spray, but it is better to keep the plant stress free by providing adequate moisture and fertilizer. It is best to minimize chemicals, especially if your goal is to provide a breeding ground for butterflies.
Buddleias are considered to be deer resistant. Deer prefer many other plants and will only feed on the butterfly bush as a last resort.
Conclusion
There are dozens of wonderful buddleias for temperate gardens. A comprehensive list of species and cultivars may be found on the Plant Delights web page link below.
Buddleias are admirable garden shrubs for any garden from Zone 5 south. Buddleias are beautifully floriferous and sweetly odiferous and will attract thousands of butterflies to your garden. You may be asking yourself, “What is the best butterfly bush for my garden?” If you want incredible yellow foliage, try Buddleia ‘Evil Ways’. For nearly red flowers, choose Buddleia ‘Miss Ruby’. If you are looking for rare, eye-popping, yellow or orange flowers, you’ll want Buddleia ‘Honeycomb’ or Buddleia ‘Orange Sceptre’. For a demure look, try the pastel colored Buddleia ‘Pink Delight’. Buddleia ‘Blue Chip’ and Buddleia ‘Ellen’s Blue’ are great compact blue-flowering buddleias. For the smaller garden, Buddleia ‘White Ball’ is a great white flowering selection a tidy compact habit. If you want to impress your gardening friends, try the truly unusual Buddleia ‘Bicolor’ or Buddleia lindleyana. Whichever one you choose, you will be sure to get a winner!
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