Jacaranda

Jacaranda is a subtropical tree in the trumpet vine family, Bignoniaceae, native to southern and central South America, with wild populations running through southern Brazil, Uruguay, Paraguay, northern Argentina, and southern Bolivia. Nurseries and street tree lists also sell it as blue jacaranda, fern tree, blue trumpet tree, and black poui, and the name is believed to mean fragrant in a native South American dialect. The fern name comes from the foliage: the leaves are bipinnately compound and 9 to 18 inches long, each primary leaflet carrying about 20 small secondary leaflets, which is why the canopy throws filtered shade. Flowers are trumpet shaped and up to two inches long, massed on panicles 12 to 18 inches long at the ends of the branches. Woody seed pods about two inches across follow the color, each holding a stack of flat, winged seeds, and they are tough enough that people gather and clean them for dried arrangements and Christmas trees.

The species is listed as Vulnerable by the IUCN in its native range, where uncontrolled logging and the clearing of land for agriculture have thinned wild stands. As a planted tree it is anything but scarce: Pretoria and its surroundings hold more than 65,000 jacarandas, which is where the nickname Jacaranda City comes from, and it is one of the most common trees in Buenos Aires. In the United States the tree is grown extensively in California, the Southwest, southeast Texas, and Florida. San Diego owes much of its purple to Kate Sessions, the horticulturist credited with importing and popularizing the jacaranda there, and it is now the official urban tree of the City of San Diego. The northern edge is abrupt: in San Francisco the tree grows only in the city's warmest microclimates, places such as Potrero Hill and the Mission District. There is also a labeling wrinkle to settle before you buy. Much of the Jacaranda mimosifolia in the nursery trade may in fact be a hybrid with J. acutifolia, a closely related species from the Andean valleys of Peru that runs smaller, carries fewer leaflets, and flowers in a more intense color. It explains why two trees sold under the same name can hold noticeably different shades of purple.

Jacaranda blooms in late spring and early summer, and the display can hold for up to two months. The published window is wide because the tree follows heat: flowers can appear any time from April through August, most often in May, while a narrower June to July window is also published. Climate type moves the peak further than latitude does, with the low deserts flowering in April and May and California's maritime climates holding off until June. In Texas the bluish purple spikes come through spring and summer without one tight peak. South of the equator the calendar flips, and Pretoria's jacarandas appear from late September until November. Gardeners who want the bed underneath to peak with the canopy choose purple flowers that open in the same weeks.

Yellow leaves and heavy leaf drop in late winter belong to the bloom cycle. In Phoenix the tree turns briefly deciduous through late winter and early spring, and in Hawaii it drops its seed pods and leaves in February and March before pushing out purple flowers in April and May. The flowers open ahead of the new flush of leaves, which is why a jacaranda in full bloom can look half dead to anyone seeing one for the first time: bare gray branches, no foliage, and color at every tip. The leaves return in summer as the flowers fade. What ends the bare stage is heat. A March heat wave above 90 degrees Fahrenheit pushed Los Angeles jacarandas into early bloom because the trees respond to temperature, and a stretch of 90-plus weather reads to a jacaranda as the signal to put out flowers even when it lands weeks ahead of the usual date.

How heavy the bloom gets is a separate question from when it starts. Warm weather brings more abundant flowers over a longer period, and cold weather cuts both. Flowering is reported to be best following a winter with several nights in the upper 30s, so a winter that never cools off can cost a tree its best spring, and heavy winter rain has produced the most spectacular spring displays in Phoenix. Both ends of the thermometer take flowers away: the species does not generally flower in Darwin, at the tropical end, and Hobart is a little too cold for it.

The most common reason a jacaranda does not flower is age, and how many years that means depends on how the tree was propagated. Grafted trees begin flowering between 5 and 7 years old, with 3 to 5 years also published. Seed-grown trees are the long wait: 7 to 14 years is normal, up to 10 years is given for a tree raised from seed, and the straight species is put at ten years of age. Newly planted trees in Australia have produced first flowers anywhere between 2 and 14 years, and one grower in Perth reported a tree planted for about 18 years that had never flowered at all. Because seedlings take so long, grafted trees and trees rooted from cuttings are the ones recommended.

After age, the usual cause is kindness. Jacaranda may flower best when grown in poor soil, so a tree standing in a watered, fed lawn is getting everything except the lean, dry conditions that push it to bloom. Climate can cap the bloom outright, and the clearest case is the coast, where growth is stunted directly on the California shoreline because cool ocean wind and a lack of heat discourage flowering. A tree that is the right age, in full sun, on lean soil, and out of the sea wind has run out of excuses, and the remaining question is what it was grown from.

Jacaranda is hardy in USDA zones 9b through 11. The cold end of that rating is where the published ranges part company: a more cautious one gives 10 to 11 with 9b called possible, and a third runs from 9b all the way up through 13b. In protected locations the tree turns up half a zone colder, in 9A, which is where most of the gambling happens: a courtyard, a south-facing wall, a block of city pavement that holds its heat overnight. Below that range a jacaranda does not stay outside through winter. The zone number is still only half the answer, because zone maps are drawn from average annual winter lows, and what hurts this tree is the single coldest night of a particular year and how long it lasts.

Established trees usually withstand occasional temperatures down to about 20 degrees Fahrenheit, and brief spells down to around 19 degrees are also reported. In the desert Southwest the figure given is higher, 27 degrees, with damage showing up during Tucson winters and the coldest winters in Phoenix. Every one of those published figures describes brief, occasional cold and assumes an established tree. Age decides the outcome. Young trees take the worst of a hard frost, and even those often rebound from the roots and regrow in a shrub-like, multi-stemmed form, which is how a zone-edge gardener ends up with a wide bush where a shade tree was planted. Heat sets its own limit in the low desert, where the trunk is highly susceptible to trunkscald injury as well as to occasional freeze injury.

Where winters are too cold to leave a tree outdoors year round, the pot is the only option, and the foliage is what you are growing. The routine is fixed by frost: the pot spends the warm months outside in sun and comes indoors each fall before frost, overwintering in a bright, cool location. That swap is the same one hibiscus growers north of the Sun Belt already run every October. Indoors, watch for aphids and whiteflies, which bother potted plants far more than trees standing outside.

The price of a jacaranda is litter, and the drop is heavy enough to decide where the tree goes. It sheds dry fruit, leaves, and flowers across the year, and that leaf and flower drop is the reason it should not be used near a pool or next to a patio where fallen flowers and shed leaves turn into a chore. Set against a royal poinciana it is the tidier tree, and it still makes a lot of leaf litter. Surface roots are the second cost, because jacaranda can form large ones. Wood strength is the third: weak wood is a listed problem for the species and storm damage follows from it, with the counterweight being early training, since a properly trained and pruned jacaranda is fairly strong wooded.

What comes back is shade, color, and a tree that asks for very little. Jacaranda is relatively drought tolerant, pest resistant, and able to grow in the small planting cutouts cities give street trees, and the shade arrives quickly because growth is fast. The large flowers pull in bees and other pollinators at a time when bee populations are deteriorating, and the tree draws birds as well. Pollen is a minor complaint, causing only slight allergy symptoms. Then there is the reason people put up with the sweeping: when the flowers drop they form a carpet of purple under the canopy, and the same litter one neighbor clears every morning is what the next one photographs. Where the drop is a deal breaker, magnolia is the other large southern flowering tree to weigh on placement.

Jacaranda needs full sun, meaning six or more hours of direct sunlight a day. Heaviest flowering and fastest growth both happen in full sun, and while small trees tolerate light shade, the flowers are what the shade costs. Morning sun with an afternoon in the shadow of a two-story house is a common setup that produces a tall green tree and nothing else, and it is worth checking where the shade will fall in ten years, not where it falls the week you plant. There is one place where sun works against the tree. In the low desert the trunk is susceptible to sunscald, so a position that throws reflected or western light onto the bark of a young tree is the wrong one, and a trunk wrap or a temporary shade board is the usual answer while the canopy is still small.

Well-draining, slightly sandy, acidic soil suits a jacaranda best, and the species tolerates sand, loam, or clay across a range from slightly alkaline to acidic as long as the drainage is real. That range covers the alkaline ground of the desert Southwest at one end and the acid sands of Florida at the other. What it will not accept is heavy, poorly drained ground. On a clay lot the answer is to plant high, setting the root ball slightly above grade so water moves away from it, which costs nothing at planting and cannot be retrofitted later.

Water is where most jacaranda failures start. Once established the tree is very drought tolerant, carrying a high drought rating and no tolerance at all for aerosol salt. Salt tolerance is rated low and water use medium overall, so a beachfront lot within reach of spray is a poor site whatever the zone map says. Deep, infrequent soaks suit an established tree far better than the daily minutes a lawn zone runs, and a mature jacaranda left on the lawn schedule is being watered for the grass. The low desert is the exception: in Phoenix the tree wants deep, regular supplemental watering, especially through the warm part of the year. The specific failure on ground that stays wet is mushroom root rot, a problem on poorly drained soil.

Give the tree room before anything else: plant a jacaranda at least 15 feet from the house, with 20 feet better, and keep it at least 15 feet from walks and driveways. The reason is underground as much as overhead, since large surface roots make jacaranda a poor choice close to structures or walkways. Set the root flare at grade so the trunk is not buried, and backfill with the soil that came out of the hole. Stake a young tree through its first year, because a strong wind can blow one over while it is still anchoring; leave the ties loose enough for the trunk to flex, and check them after every storm. Water it during dry periods until it is well established, and after that only in drought, if at all. The spacing call is the one decision on this list that cannot be revisited once the trunk is up.

Prune a jacaranda for structure while it is young, and do the cutting after it flowers. Pruning is needed for strong structure, and the tree is susceptible to breakage without it. Left alone, a young tree develops several co-dominant stems, often with included bark, which is the split waiting to happen in the first real storm. The schedule is specific: cut back the branches competing with the leader every three years until the tree is 15 to 20 years old, and as it matures keep branches to less than half the diameter of the trunk. Timing follows the bloom, since the needed pruning is done after flowering in spring and early summer, which leaves that season's flowers on the tree. A tree that came back from the roots after a freeze arrives multi-stemmed, and the same leader rule settles it: pick the strongest stem and cut back the ones competing with it.

Feeding is rarely what a jacaranda is short of, because the tree grows fast without help. In its native environment it gains up to 10 feet of height a year, and that rate drops in cooler climates, while the maximum recorded for landscape trees is about 36 inches a year. Most US yards land between those two figures, nearer the lower one where nights stay cool and the season is short. On Florida sand a granular feed three times a year, in spring, summer, and autumn, is the schedule that gets recommended, and that is the heaviest case anyone makes for fertilizer on this species.

A jacaranda finishes at 25 to 50 feet tall, and how wide it finishes depends on which source you read. Height is the settled part: a mature tree measured at 40 feet tall and 30 feet across, full maturity described as 50 feet with a trunk 20 inches thick, and an outer record of about 66 feet on old specimens. Spread is where the numbers split, and the split is wide enough to change where the tree goes. UF/IFAS gives 45 to 60 feet; Missouri Botanical Garden gives 15 to 30 feet; a third published range narrows it to 15 to 25 feet, and the largest canopy width on record is 30 feet. Part of the gap is what got measured, since an open-grown tree with room on every side takes a different shape from a street tree in a sidewalk cutout. Site the tree for the wide figure and a narrow crown costs you nothing.

Almost everything sold as a jacaranda in the United States is the straight species, the blue jacaranda, which holds an Award of Garden Merit. Its purple-blue spikes are the color people mean when they say jacaranda, and the two named forms behind it are easy to tell apart because each changes one obvious thing. 'Alba' changes the color: it is a white-flowered cultivar with a longer blooming period and sparser flowers, holding its bloom across more of spring and summer than the species. 'Bonsai Blue' changes the size: a true dwarf at 10 to 12 feet tall and 6 to 8 feet wide, semi-evergreen with fern-like foliage that takes pruning well, and it flowers about two years after grafting. Anything else offered under the name is the species again, grown from seed or from a graft, and that difference is what sets how long you wait for the first flowers.

Jacaranda is grown from softwood cuttings, grafting, or seed. Seed is the easiest of the three to start and the slowest to pay: fresh seed germinates at 50 to 92 percent and generally needs no pretreatment, and a lone tree sets viable pods on its own, since the species is self-compatible. That combination is why volunteer seedlings turn up under street trees and why so many home-raised jacarandas exist with nobody sure what they will do. Lifespan is the other end of the same story. Jacarandas can reach two hundred years of age. A Sydney tree planted around 1850 was still standing at over 175 years old, fenced off with ropes to protect it, and of 115 planted on one California campus in 1988, 65 were still standing decades later.

No pests are of major concern on a jacaranda. The insects that do turn up are ordinary ones, scale and aphids, and the California susceptibility list adds the invasive shot hole borer alongside phytophthora and root rot. A bacterial problem specific to the species is also on record. The pattern in that list is drainage, because both diseases on it are root diseases of wet ground, so a tree that thins out, wilts through the heat of the day, and sheds leaves off season is worth diagnosing from the soil upward before anything gets sprayed at the canopy.

Jacaranda is not listed as being toxic to pets. Extension plant records tag the species non-toxic for cats, dogs, and horses, and its toxicity is rated benign. There is one gap worth knowing about, and it sits on the list most owners check first: the ASPCA database carries no entry for Jacaranda mimosifolia at all. Its only jacaranda is Caroba, Jacaranda procera, a different species in the same genus, marked non-toxic to dogs, cats, and horses. That page settles nothing about the tree in your yard either way, so the direct statements from the extension services are the better ground to stand on.

What a jacaranda means comes from when it flowers. In the southern hemisphere the bloom lands at the end of the academic year, so the tree in flower is known as the exam tree, and students in southeast Queensland call the season purple panic. A jacaranda planted in a Sydney university quadrangle in 1928 carries the same warning for anyone who has not started studying, while the Pretoria version of the folklore is gentler: a flower that drops on a student's head means passing every exam. A South African radio station is named for the tree. The travel history behind all that is short and entirely ornamental. The first specimens went from Rio to Britain around 1818, jacarandas were listed for sale in Sydney by 1861 and Brisbane's earliest tree went in during 1864, and the species stayed admired and rare across Australia until someone worked out how to propagate it in 1868. Every city that took it up afterward built a season around the same few weeks.

1. The dwarf 'Bonsai Blue' was not bred for the job. It was found as a chance seedling in a private garden in Nichinan-shi, Miyazaki, Japan, in May 1995.
2. White jacarandas are worth hunting. Los Angeles has a rare white cultivar, with some trees rumored to stand in a non-public part of the county arboretum, and about one hundred white jacarandas are planted among the purple ones in the Groenkloof area of Pretoria.
3. The purple season has been moving. In the 1920s Pretoria's jacarandas bloomed in mid-November, while today they open in early September, a shift researchers link to a warming climate.

Related Guides & Flowers

Blue flowers

Where the jacaranda's blue-purple sits among the garden plants that read as true blue.

Types of flowers

The full index of flower profiles on the site, sorted by kind.

Lilac

The cold-climate answer to a purple spring, for gardens far north of jacaranda country.

Magnolia

The other large southern flowering tree, with the same placement questions and a heavier leaf.