Summer Lilac (Buddleja davidii)

Butterfly Bush, Orange-Eyed Butterfly Bush, Summer Lilac

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Butterfly bushes (Buddleia davidii) are grown for their long panicles of colorful flowers and their ability to attract butterflies and beneficial insects. They bloom in spring and summer, but the naturally attractive shape of the shrub and evergreen foliage keep the bush interesting, even when it is not in bloom. These tough plants tolerate a variety of conditions and are hardy in USDA plant hardiness zones 5 through 9. Find out more about butterfly bush planting and care.

I. Appearance and Characteristics 

Buddleja davidii (spelling variant Buddleia davidii), also called summer lilac, butterfly-bush, or orange eye, is a species of flowering plant in the family Scrophulariaceae, native to Sichuan and Hubei provinces in central China, and also Japan. It is widely used as an ornamental plant, and many named varieties are in cultivation. The genus was named Buddleja after Reverend Adam Buddle, an English botanist. The species name davidii honors the French missionary and explorer in China, Father Armand David, who was the first European to report the shrub. It was found near Yichang by Dr Augustine Henry about 1887 and sent to St Petersburg. Another botanist-missionary in China, Jean-André Soulié, sent seed to the French nursery Vilmorin, and B. davidii entered commerce in the 1890s.

  1. davidii was accorded the RHS Award of Merit (AM) in 1898, and the Award of Garden Merit (AGM) in 1941.

Buddleja davidii is a vigorous shrub with an arching habit, growing to 5 m (16 ft) in height. The pale brown bark becomes deeply fissured with age. The branches are quadrangular in section, the younger shoots covered in a dense indumentum. The opposite lanceolate leaves are 7–13 cm (3–5 inches) long, tomentose beneath when young. The honey-scented lilac to purple inflorescences are terminal panicles, < 20 cm (8 inches) long. Flowers are perfect (having both male and female parts), hence are hermaphrodite rather than monoecious (separate male and female flowers on the same plant) as is often incorrectly stated. Ploidy 2n = 76 (tetraploid).

Buddleja davidii cultivars are much appreciated worldwide as ornamentals and for the value of their flowers as a nectar source for many species of butterfly. However, the plant does not provide food for butterfly larvae, and buddlejas might out-compete the host plants that caterpillars require.

The species and its cultivars are not able to survive the harsh winters of northern or montane climates, being killed by temperatures below about −15 to −20 °C (5 to −4 °F).

Buddleja davidii has been designated as an invasive species or a “noxious weed” in a number of countries in temperate regions, including the United Kingdom, the Republic of Ireland and New Zealand. It is naturalized in Australia and in many cities of central and southern Europe, where it can spread on open lands and in gardens.

Summer Lilac (Buddleja davidii)

II. How to Grow and Care

Sunlight

Butterfly bush needs full sun (at least six hours daily) and will become weedy and sparse if grown in shady conditions.

Temperature and Humidity

Butterfly bush thrives throughout its hardiness zone range (zones 5 to 9), but expect it to die back to ground level in winter in zones 5 and 6.

Watering

This plant likes a medium-moisture environment and will do poorly at either extreme—intolerant of drought or boggy locations that don’t drain well. They will thrive on 1/2 inch of water by rain or irrigation each week.

Soil

This plant will thrive in any average, well-drained soil that gets an average amount of moisture. It prefers a soil pH from 6.0 to 7.0, slightly acidic to neutral.

Fertilizing

This plant needs no fertilizer, other than a thin layer of compost spread over the root zone each spring.

Planting Instructions

Pruning

The spent flower spikes of butterfly bush should be removed promptly after flowering to stimulate continued blooming right up to frost and reduce the chances of self-seeding. This plant grows rapidly, and pruning it all the way to ground level each spring stimulates vigorous growth and profuse flowering. This is often a good idea even in warmer regions where the plant grows as an evergreen shrub.

Propagation

It’s rare that you would seek to propagate this bush, since it spreads so readily, but if you do, collecting the seeds heads will give you plenty of seeds to replant wherever you wish.

But propagation by seed is not possible if you have wisely chosen a sterile, seedless variety of butterfly bush for your garden. To propagate one of these non-patented varieties, rooting branch cuttings is the best approach. Here’s how to do it:

  • In summer, use sharp pruners to cut a 4- to 6-inch segment from a healthy branch tip. Make the cut just below a healthy bud. Remove the leaves from the bottom one-third of the cutting.
  • Dip the cutting in rooting hormone powder, then plant it in a small pot containing a mixture of peat moss and perlite. Moisten the potting mix.
  • Put the plant in a plastic bag to hold in moisture, and set the pot in a bright location, but out of direct sunlight.
  • In three to six weeks, roots should develop (tug lightly on the stem; if you feel resistance, roots are present). At this time, you can transplant the cutting into a larger container or transplant it into the garden.

How to Grow from Seed

Butterfly bush self-seeds so readily that “how to do it” is almost laughably obvious. It’s an easy matter to transplant the volunteer seedlings that sprout up around a parent plant. You can also harvest seeds from dried flower heads and store them to plant in the desired location the following spring.

More likely, though, you’ll be planting purchased seeds for one of the sterile cultivars now available. In that case, direct sowing the seeds in the desired location will result in germination and sprouting within a few days, and fully mature plants by the end of the first growing season.

Potting and Repotting 

Most butterfly bush varieties are too large to make good container plants, but there are several dwarf varieties, such as the Lo and Behold and Pugster series that are only about 2 feet tall and make decent container plants. Use a large pot (any material) that is at least twice as deep as the nursery container, and fill it with a standard potting mix blended with some compost.

In cold winter zones, the potted butterfly bush should be cut down to soil level for the winter and moved into a sheltered location to protect the roots for the winter.

Overwintering

These are sturdy, durable plants that don’t need much in the way of winter protection. Even if the plants die back to the ground due to cold, they will usually assume the role of herbaceous perennial, sprouting up again in the spring.

It’s a good idea to cut off flower heads in the fall to prevent self-seeding. In regions where the plant is borderline hardy, a 2- to 3-inch layer of mulch may help protect the roots over the winter.

How to Get Butterfly Bush to Bloom

In moderately good growing conditions (plenty of sun, moist but well-draining soil) butterfly bush will display plenty of flowers from early summer right up to fall. When plants don’t bloom, it’s because of one of these conditions:

  • Not enough sun. These are sun-loving plants that will not bloom if they don’t get at least six hours of daily sun.
  • Too much or too little water. Butterfly bush likes plenty of moisture, but not sogginess. Excessive moisture can cause root rot which prevents flower buds from forming. And drought can also cause the plant to conserve energy by withholding flowers.
  • Summer is too cool. Butterfly bush thrives in temperatures 75 degrees Fahrenheit or above, and if your summer has been unseasonably cool, the plants may withhold flowers for that year.
  • Planted too deeply. If potted nursery plants are planted too deeply, they may not bloom in their first year, though they usually self-correct by the following season. Plant nursery specimens at the same height they were growing in their containers.
  • Beetle or grasshopper damage. An unusually large infestation of feeding beetles or grasshoppers can devour the flower buds. The plants generally recover for the next year.

Pests and Diseases

Common Pests & Plant Diseases

There are no serious pest or disease problems with butterfly bush, although spider mites can be an issue and nematodes can be a problem in the South.

Spider mites cause small spots to appear on leaves, gradually causing leaves to turn gray or bronze. Silky webs may also appear on the leaves. Left alone, predatory insects often arrive to keep spider mites in check. Or, you can use horticultural oils or pyrethrin-based insecticides to control them, though be aware that these may also kill the beneficial insects.

Nematodes cause yellow patch-like damage to leaves. There is no effective treatment, so affected plants will need to be removed and destroyed.

Common Problems 

The most common complaint with butterfly bush is, without question, its tendency to spread aggressively, even uncontrollably. For many people, the best answer is to remove the plant and replace it with one of the seedless, sterile varieties that are increasingly available.

You can minimize the rampant spread by routinely clipping off flower heads before they dry out and scatter seeds, by cutting down all stems at the end of each growing season, and by diligently plucking out the volunteer seedlings as you spot them.

III. Uses and Benefits 

The butterfly bush is considered a very versatile flower which can be found in cottage, children’s, butterfly, drought-tolerant, and pollinator gardens. It is particularly popular among gardeners for its planting versatility in borders and hedges, attractiveness to pollinators, and resistance to animals. Plants such as Heliotrope and Lantanas make good companion plants for the butterfly bush.

Summer Lilac (Buddleja davidii) Details

Common name

Butterfly Bush, Orange-Eyed Butterfly Bush, Summer Lilac

Botanical name

Buddleja davidii

Family

Scrophulariaceae

Species

davidi

Origin

Tibet to S. Central China

Life cycle

Plant type

Hardiness zone

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Sunlight

Maintenance

Soil condition

Soil ph

Drainage

Growth rate

Spacing

6 – ft. – 12 ft.

Harvest time

Flowering period

Height

5 ft. – 12 ft.

Width

5 ft. – 12 ft.

Flower color

,

Leaf color

,

Fruit color

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Fruit type

Leaf benefit

Flower benefit

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