How to Grow a Butterfly Bush
The butterfly bush is an elegant specimen known for its long panicles of colorful flowers. Flowering from spring until late summer, as the name suggests the plant draws scores of butterflies. It also attracts hummingbirds and numerous other pollinators into your garden. Sometimes known as the summer lilac or buddleia, the evergreen butterfly bush is hardy in USDA Zones 5 to 9.
Originating in Japan and China, the butterfly bush is a quick growing plant producing masses of green foliage and long floral spikes every year. Despite its vigorous growth habit the plant keeps its shape well, making maintenance easy and straightforward.
This guide will take you through everything you need to know about adding a butterfly bush to your garden.
The summer lilac can be an fragrant and colorful addition to the garden. Just be prepared to control the plant’s potentially invasive growth habit.
Warning. Not to be confused with butterfly weed, the butterfly bush is considered invasive in some areas. The state of Oregon has completely banned the sale of the plant. Check with your local extension office for the guidelines in your area before planting.
If you are unable to plant a butterfly bush there are a number of equally attractive, native alternatives. These include:
Different Butterfly Bush Varieties
There are many hundreds of different butterfly bush varieties available. Most are variations of Buddleia davidii. These grow to about 20 ft and tolerate temperatures as low as – 20 ℉. As well as being cold tolerant they also cope well in warmer climates. This reliability makes them a popular choice for many gardeners.
Whatever your growing conditions you are almost certain to find at least one variety that is suitable. For example, if you are growing buddleia in a cooler climate, Black Night is a reliable variety. Reaching a height of about 15 ft, the plant produces elongated panicles of dark flowers.
Purple Ice Delight is also cold tolerant. A dense bush-like plant that rarely exceeds 8 ft in height, it produces masses of dark purple flowers with pink highlights. For something a little brighter, the pink flowering Pink Delight shares a similar growth spread and habit. Another cold hardy variety is the purple flowering Royal Red. A compact cultivar, it rarely exceeds 6 ft in height.
In warmer areas, particularly USDA Zones 7 to 10, the hybrid Lochinch is a great choice. A large variety, reaching heights of upto 15 ft, it produces attractive lavender colored flowers which sit above masses of elegant silver backed foliage.
White Profusions is another cultivar that thrives in warm conditions. When fully mature the plant is about 10 ft tall. As the name suggests when in flower the plant is covered in masses of white flower clusters.
Smaller cultivars which thrive in warm conditions include Ellen’s Blue and the rose pink flowering Summer Beauty. Both are dwarf cultivars which achieve a maximum height of about 4 ft.
Other popular dwarf varieties include:
All of these rarely exceed 5 ft.
While most varieties flower in shades of purple or pink, with a little extra effort you will be able to find cultivars in more unusual shades such as white or yellow.
Many gardeners like to grow native plants. These are often more suited to your growing conditions and are less likely to succumb to common pests and diseases.
Native butterfly bush varieties include:
- Rio Grande, which is native to Texas and Arizona
- Orange Woolly, native to the Chihuahuan Desert
- Wand, another Texas native
- Escobilla, native to New Mexico, Arizona and Texas
Due to the Buddleia’s quick, sometimes invasive, growth habit, sterile varieties are becoming increasingly popular. Blue Chip is a popular sterile variety. A smaller cultivar, it usually reaches a height of 3 ft but this can increase to 6 ft in warm conditions.
Many garden stores sell young plants or seed packets. You can also purchase seeds and transplants from specialist plant nurseries.
Growing from Seed
Seeds can be started at any time of year.
Fill your seed tray with a fresh, peat based seed compost. Moisten the soil. Sow the seeds as thinly as possible. The buddleia needs lots of light to germinate so there is no need to cover the seeds.
Seeds need to be exposed to a period of cold temperatures before they can germinate. Commercially sold seeds have already been through this process, others will require you to do the chilling. To chill your seeds, place them in a cold place, such as a refrigerator. The temperature should average 35 to 41 ℉. Chill the seeds for 4 weeks before removing the trays to a warmer place.
The temperature around your seeds should now average 64 to 71 ℉. You can also place the trays in a propagator or on a heat mat to ensure a constant, warm temperature. The Vivosun Seedling Heat Mat comes with a digital thermometer. This helps you to ensure an even temperature around your delicate seedlings. As well as maintaining an even temperature you should also keep the soil evenly moist.
Growing from seed can be tricky. Starting the seeds off undercover allows you to better control the conditions around the growing seedlings.
Germination should occur within 20 to 30 days. Following germination, continue to protect your growing seedlings. As they develop, gradually increase the ventilation around the seedlings.
When the seedlings are large enough to handle, thin them out and transplant into small pots filled with fresh potting soil. Grow the transplanted seedlings on in a light, cool position away from the direct glare of the sun.
Harden off your seedlings in the spring before transplanting into their final position.
Planting a Butterfly Bush
The butterfly bush does best in a sunny or partial shade position. Avoid planting in overly shady positions, the lack of light can inhibit flowering.
Before planting take the time to properly prepare the soil. This is particularly helpful when planting long lasting bushes such as the buddleia. Plant in soil that is light and well draining. Working organic matter such as well rotted manure can help to enrich the soil and improve drainage.
Don’t plant your butterfly bush in a heavy or poorly draining soil. These can be slow to drain, causing roots to sit in water and become rotten.
A soil test kit tells you the pH content of your soil, ideally it should be between 6.0 and 7.0, as well as any amendments you need to make.
The buddleia is best planted in the spring. In warmer areas you can also plant in the early fall, well before the first predicted frost date.
To plant a buddleia, dig a hole in the soil large enough to comfortably hold the root system. If you are unsure how big the hole should be, put the pot holding the plant in the hole. It should comfortably fit inside.
When you are happy with the size of the hole, work some compost into the bottom. This gives the plants a nutritional boost, helping to reduce the potential negative effects of transplant shock.
Remove the plant from its container. You may need to squeeze the sides to loosen the soil, this helps you to easily slide the plant out. Gently tease apart the roots before positioning in the centre of the hole. The top of the root system should be at soil level.
Backfill the hole and firm down the soil. Water well.
If you are planting more than one butterfly bush you should space them at least 4 ft apart. Some varieties have a spread of upto 15 ft. Consult the information on the plant label before planting, this tells you how large your plant may become and also gives you the exact spacing information.
Planting in Pots
The butterfly bush can also be grown in a pot. This helps to contain its spread.
Larger varieties should be planted in large pots or old barrels. Smaller, dwarf varieties don’t need quite as much room. Try to select a pot that is both large enough to hold the buddleia’s large root system and heavy enough to prevent toppling. It should also have plenty of drainage holes in the bottom.
Fill the pot with a light, potting soil mix and plant as described above.
Placing the pot on a plant caddy, such as the Amagabeli Metal Plant Caddy enables you to easily move it around your home and garden.
Caring for a Butterfly Bush
Once planted, this is a pleasingly low maintenance plant. The butterfly bush is one of the latest spring flowering plants to break its winter dormancy. This means that buds can seem slow to emerge. But be patient, the plant will soon flower profusely.
Typically late to emerge from its winter dormancy, once it does begin to grow the plant enjoys a vigorous growth habit.
When to Water
Once established buddleia plants only require watering during dry periods, if the soil begins to dry out. When the plants are actively growing or in flower they will require more frequent watering than during the dormant fall and winter months. During prolonged dry spells use a garden hose to soak the soil and drench even the deepest roots.
Plants growing in containers require watering more frequently than those in the ground. Planting in self watering pots can help to reduce the frequency with which you need to water.
Fertilizing a Butterfly Bush
Despite the plant’s vigorous growth habit you only need to fertilize your butterfly bush if it is growing in poor soil. The plants can also benefit from one dose of balanced fertilizer once a year starting a year after planting.
Be careful not to over fertilize your flowers. This can encourage too much foliage to emerge at the expense of flower production.
Instead of applying balanced fertilizer, plants growing in pots may benefit more from an application of slow release fertilizer. This can be added to the soil in the spring and helps to sustain foliage and flower production throughout the growing season.
How to Prune a Buddleia
As we have already noted, these plants have a vigorous growth habit. If left unchecked they can become invasive. While measures such as growing in containers or only planting sterile varieties can help to control the spread, pruning is also necessary if you want to keep your butterfly bush under control.
Larger varieties require more regular pruning than small or dwarf cultivars.
Deadhead spent flower clusters regularly through spring and summer to prevent pods developing. Mature pods can split allowing the seeds to be spread by the wind across a wide area. If the plant does set seed in an unwanted position don’t just cut it off at ground level. You also need to dig down to remove the roots as well as the top growth.
Deadheading the plants also encourages more flowers to emerge. Similarly, pinching out growing tips helps to encourage more bushier growth to form.
If you don’t want to spend time regularly dead heading your butterfly bush, try growing sterile varieties. These don’t set seed and are considered noninvasive.
To keep plants healthy, prune them down to the ground every year. This also helps to prevent them from overgrowing a space. In cooler climates, especially in areas where the temperature falls below 0 ℉, the bush naturally dies back. Here simply prune away the dead growth in early spring, before new growth emerges.
In milder climates you can prune the plant down to about 3 inches above the ground in early spring. Pruning back to the ground helps to encourage new, compact growth to emerge.
Plants growing in pots can also be cut down, to about 10 inches above the ground.
Don’t prune the plants in the fall. Allowing the old growth to remain in place helps to protect the plant from icy winds and cold temperatures. Instead prune in early spring. Just be careful not to prune away new growth, this can hamper flower production.
While the plants are largely cold hardy, they can still benefit from a little extra winter protection. Apply a 2 to 3 inch thick layer of mulch around the bottom of the plant. Aim to cover the entire root area. This helps to prevent the soil from freezing.
Plants growing in containers can be moved to a more sheltered area.
In very cold climates wrap the plants with bubble wrap or a horticultural fleece such as a Haxnicks Easy Fleece Jacket.
To support insect and butterfly life, as part of a butterfly friendly garden, there are a number of plants that can compliment a butterfly bush. Reliable companion plants include:
- Black Cherry
- Gray Dogwood
- Northern Spicebush
- Tulip Poplar Tree
Planting your butterfly bush with a mix of other flowers can help to increase the attraction for butterflies and other beneficial insects.
While the butterfly bush compliments a number of plants, avoid planting it too closely to small or slow growing plants. The vigorous growth habit of the buddleia can smother other, slow growing plants.
How to Propagate a Butterfly Bush
There are a number of different ways to propagate a butterfly bush.
While the plants easily set seed, most varieties are hybrid. This means that seeds grown from the parent plant are often disappointing and are rarely true to type.
Dividing a Buddleia
The easiest way to propagate the plants is by dividing the root system. Divisions can be taken at any time of year, as long as the plant is in good health. However, the process is best done in the fall, when the soil is warmer than the air for at least part of the day.
Soak the soil the night before you divide. This makes digging up the roots easier.
With a robust shovel dig deeply down, all around the plant. You are trying to raise as much of the root system in one piece as possible. Use the shovel to carefully lift the plant and the root system from the soil.
Use a sharp pair of garden scissors to divide the root section into several sections. Each section should have some roots and stems.
Replant the divided sections as quickly as possible in pots or around the garden. Plant the divisions as quickly as possible to prevent the roots from drying out. Water well and keep the soil evenly moist until the plants are established and new growth is visible. An application of balanced fertilizer can help speed up the process.
One of the easiest ways to propagate a butterfly bush is by taking cuttings. Take branch tip cuttings from healthy stems in the spring or summer. The cutting should be about 3 inches in length.
Remove the foliage from the bottom half of the cutting and dip in rooting hormone. Plant the cutting in a pot filled with moist potting soil and place in a partial shade position. Keep the cutting warm and the soil moist.
Roots begin to form within a few weeks. To check for roots gently tug the cutting. If you feel resistance it means that roots are developing. Allow the cutting to grow on in its sheltered position until you are ready to plant out in the spring.
Common Butterfly Bush Problems
These plants are pleasingly easy to grow and rarely suffer from any major problems.
Root rot can be caused by planting in poor draining soil. Yellowing foliage as well as twig and stem dieback are all signs of root rot. Amending the soil before planting, or planting in an elevated position to encourage excess water to drain away, can help to prevent this issue.
Yellowing foliage can also be caused by planting in overly acidic soil. Use a soil test kit to measure the pH level of your soil before making any necessary amendments.
Another common cause of yellowing foliage is a spider mite infestation. A foliar fertilizer or an application of homemade insecticidal soap cures infestations. Stubborn or large infestations may require repeated treatments.
Caterpillars can often be found on the foliage of the plants. While unsightly, caterpillar infestations rarely do major damage.
Japanese beetles may also feed on your plant. Use traps or handpick the pests from the plant.
During cool periods downy mildew, which forms on foliage inhibiting photosynthesis can be a common problem. You can prevent downy mildew by watering the plants early in the morning and keeping the foliage as dry as possible.
Fast growing and reliable, buddleia will attract scores of butterflies and pollinators to your garden.
Low maintenance and attractive, the butterfly bush is ideal for perennial beds or borders. Equally at home in a pot near a patio or on a balcony, the elegant flowers of the buddleia bring color, fragrance and plenty of butterflies to your garden.