Shrub · Scrophulariaceae
Butterfly Bush
Buddleja davidii
Site it in full sun and prune it hard each spring, and the butterfly bush fills with flowers and pollinators all summer.
Full sun
Every 7–14 days
USDA 5–9
6–12 ft · 1.8–3.7 m
Overview
Few shrubs concentrate pollinators the way a flowering butterfly bush does. The long, tapering spikes open from summer into early fall, and their nectar draws butterflies, bees, and hummingbirds in numbers. Growth is fast and undemanding in full sun, drought tolerance develops once the roots establish, and the plant asks little maintenance in exchange.
Expect a large, loose-framed shrub. Plants reach 6 to 12 feet (1.8 to 3.7 m) tall and often spread wider still, with arching stems that flower on the current season's growth. That flowering habit dictates the management: cutting back hard each spring drives vigorous new shoots and the heaviest flower display.
The plant carries one genuine drawback to weigh before planting. The common species self-seeds aggressively and has escaped cultivation to become a regulated noxious weed in states including Oregon and Washington. Responsible cultivation comes down to selecting a low-seed cultivar and removing spent flowers before they mature seed.
Care
The short version: full sun and average, well-drained soil, deep but infrequent watering once established, a hard cut in late winter, and regular deadheading through summer to sustain bloom and limit seed set.
Light
Butterfly bush requires full sun, ideally 6 or more hours daily, since flower production scales with light. It persists in part shade, but the result is poor: leggy, sparse growth and far fewer of the spikes that attract pollinators.
Water
Water new plants regularly through the first season so the root system establishes, then taper off. Once settled it is drought tolerant and needs only a moderate soak every 7 to 14 days. Keep the soil on the drier side rather than saturated, because waterlogging excludes oxygen and triggers root rot.
Soil
It accepts nearly any average, well-drained soil and tolerates a wide pH band from 6.0 to 8.0. Poor drainage is the one condition it will not survive, so work grit or compost into heavy clay before planting to keep the roots aerated.
Temperature
This is a tough, cold-hardy shrub rated for roughly -20°F to 100°F (-29°C to 38°C) across zones 5 to 9. Toward the cold end of that range it commonly dies back to the ground each winter, then resprouts from the crown in spring.
Humidity
Ambient outdoor air suits it, so there is no humidity target to manage. Good airflow matters more than any reading, because moving air keeps the foliage drier and discourages mites and leaf problems.
Feeding
Feed sparingly. One spring application is sufficient, and excess fertilizer drives vegetative growth at the expense of flowers by favoring leaf over bud. In reasonable soil it frequently needs no feeding at all.
Pruning
Because it flowers on new wood, cut it back hard in late winter or early spring, to within about a foot of the ground, which forces the strongest growth and the largest flowers. Then deadhead spent spikes through summer to prolong bloom and to prevent the plant from seeding itself around.
Repotting
Butterfly bush is a large shrub seldom maintained in a container for long. If you do grow one in a pot, repot only when roots circle the rootball, emerge from the drainage holes, or water runs straight through, all indications it has outgrown the container.
Size & spacing
Allow this shrub generous space. Plants reach 6 to 12 feet (1.8 to 3.7 m) tall and spread 4 to 15 feet (1.2 to 4.5 m) wide, so set them well apart and clear of paths and smaller plants they would otherwise overshadow.
When to plant
Butterfly bush follows a straightforward annual cycle. Plant new specimens out in spring after the last frost, prune established shrubs hard before growth resumes, and the flower spikes will run from summer into early fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Late winter to early spring (8-10 weeks before last frost) if growing sterile-permitting seed; species seeding is discouraged where invasive.
- Plant: Spring after last frost
- Harvest: Summer through early fall (June to September)
Hardiness
USDA hardiness zones: 5–9
Temperature: down to -29°C
Troubleshooting
An established butterfly bush has few real problems, and most trace to one of three causes: waterlogged roots, drought stress, or a skipped spring pruning. Match the symptoms below to the cause and intervene before the plant declines.
Wilting and dieback in ground that holds water
Waterlogged soil starves roots of oxygen and brings on root rot, so the canopy reads as drought-stressed even while the soil stays wet, because rotted roots can no longer take up water. Correct the drainage and cut back on irrigation, then incorporate coarse grit where the bed runs to heavy clay. On sandy coastal soils nematodes produce the same decline, and plants that far gone are best removed and replaced.
Fix:
- Improve drainage and stop overwatering
- Plant in well-drained soil; amend heavy clay before planting
- Remove and replace severely affected plants in infested ground
Stippled, bronzed foliage threaded with fine webbing
Read this as spider mites, pests that thrive on the cell-sap of plants already weakened by heat and drought stress. A forceful jet of water physically dislodges the colonies, and keeping the root zone watered removes the drought stress that let them build up. Persistent populations respond to insecticidal soap or horticultural oil applied to the foliage.
Fix:
- Spray foliage with a strong jet of water to dislodge mites
- Keep plants adequately watered to reduce drought stress
- Apply insecticidal soap or horticultural oil to affected foliage if needed
Sparse flowering on long, drawn-out stems
Weak bloom traces to one of two causes: too little light, or flowering wood that has aged out. Site the shrub for at least 6 hours of direct sun to fuel flower production, then prune hard in late winter or early spring, because buds form only on new wood the plant grows that season. Deadheading the faded spikes through summer redirects energy into further bloom.
Fix:
- Move or site in full sun
- Cut back hard in late winter or early spring since it blooms on new wood
- Deadhead spent spikes to encourage continued bloom
Toxicity
Reassuring for pet owners: butterfly bush is not poisonous to cats, dogs, horses, or people, and it does not appear on the ASPCA toxic-plant lists. The real concern is invasiveness rather than toxicity, because the common species naturalizes into the wild and is a regulated weed in some states. The sap can irritate skin, so wear gloves while pruning.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
Butterfly bush carries no listing on the ASPCA toxic plant index, so a cat that samples a leaf faces no toxic risk. Any plant eaten in volume can provoke transient drooling or mild gastrointestinal upset, but those signs resolve without treatment.
Dogs Safe
No toxin in this shrub affects dogs, so chewed foliage causes no poisoning. The one realistic concern is the generic one for any plant: a short-lived stomach upset if a dog consumes a large quantity.
Horses Safe
There are no records of toxicity in horses. The woody, bitter stems are unpalatable, so horses generally bypass the plant and graze elsewhere.
Rabbits Safe
The plant holds no poison for rabbits, so a few sampled leaves do no harm. Limit any greens to a small ration so they do not displace the hay and pellets that should form the bulk of the diet.
Livestock Safe
Cattle, goats, and sheep can browse around a butterfly bush without risk of poisoning, and the woody growth is unappealing enough that they rarely target it.
Birds Safe
The plant presents no toxic hazard to birds. Its nectar attracts butterflies and hummingbirds, but the prolific seed it produces is the mechanism by which it escapes into the wild where it is unwanted.
People Safe
No part of butterfly bush is significantly poisonous to people, and it offers nothing edible in any case. The sap can irritate sensitive skin on contact, so wear gloves before any heavy pruning.
No special toxicity handling required; wear gloves if pruning to avoid skin irritation from sap.
Varieties
Butterfly bush cultivars number in the many, and the ones worth seeking out offer either a distinctive flower color or a low seed set that keeps them in bounds. A few stand out by name.
Black Knight
A long-established cultivar valued for flower spikes in a purple so dark it reads as nearly black.
Lo & Behold 'Blue Chip'
A dwarf, compact selection whose viable seed output is low enough to satisfy Oregon's seedless butterfly bush requirements.
Miss Molly
An interspecific hybrid bearing deep red-purple flowers, verified as non-davidii and therefore exempt from Oregon's noxious weed regulation.
How to propagate
Butterfly bush propagates readily, both from cuttings taken deliberately and from seed you will usually want to suppress.
Stem cuttingsEasy
Softwood cuttings in spring to early summer; hardwood cuttings during dormancy in late fall through early spring · Softwood cuttings root in about 2-5 weeks
Vegetative cuttings reproduce a butterfly bush reliably and reproduce the parent cultivar exactly, since the new plant is a clone. Take softwood tips in spring or early summer, or hardwood pieces during dormancy from late fall into early spring. Apply rooting hormone to the cut end, hold the medium evenly moist, and softwood cuttings root in about 2 to 5 weeks.
SeedEasy
Self-seeds readily in the garden · One growing season to a small plant
Unchecked, the species self-sows widely, and a volunteer seedling reaches a small plant inside one growing season. That readiness is the liability, because the wild species is invasive and regulated in parts of the country. Do not sow the straight species where it is classed as a noxious weed, and deadhead to keep it from seeding into the wild.
Myths
Butterfly bush is always a harmless choice for the butterfly garden.
The flowers supply nectar to adult butterflies, but the foliage is no larval host, so the plant serves only one stage of their life cycle. The greater problem is fecundity: a single flower cluster releases over 40,000 seeds, and that output has let it naturalize into the wild and earn regulated noxious weed status in Oregon and Washington. The sound approach is to plant a sterile or seedless cultivar, or a native nectar shrub, and deadhead the spent spikes so seed never reaches the landscape.
Butterfly bush blooms on old wood, so you should never cut it back hard.
It flowers on new, current-season wood, which is precisely why hard pruning improves rather than harms it. Cutting close to the ground in late winter or early spring forces vigorous fresh shoots that carry larger flower spikes. In the coldest zones the plant frequently dies back to the ground on its own, accomplishing much the same renewal.