Aralia Leaves Curling
Aphids and late frost are the most common reasons aralia leaves curl. This guide shows you how to identify each cause and keep Japanese angelica tree producing its dramatic tropical-looking canopy of compound leaves through summer.
1. Aphids
Aphids are by far the most common and damaging pest of aralia in UK gardens. Aralia elata and its relatives produce their entire season's canopy of large, soft compound leaves in a very short period in late spring, and this mass of tender new growth attracts large aphid populations almost immediately. Infestations can be severe enough on young plants to cause significant leaf distortion and curl across the entire canopy.
What to look for
Young leaflets at the tips of the compound leaves curl and crinkle, giving the canopy a puckered, distorted appearance. Part any curled leaflets to find dense colonies of pale green, yellowish, or black aphids on the undersides and around the growing points. The sheer scale of the aralia's leaf area means that enormous quantities of honeydew can accumulate, coating lower leaves and any surfaces beneath the tree with a sticky film that quickly develops black sooty mould. Ants moving busily up and down the spiny stems are a reliable sign of active aphid colonies. The foliage may smell faintly of honeydew during heavy infestations.
What to do
On established trees, natural predators including ladybirds, lacewings, hoverfly larvae, and parasitic wasps will manage aphid populations effectively without intervention, though the large leaf area and fast early-season population growth means it can take several weeks for predator numbers to build sufficiently. On young trees in their first three years, where the total leaf area is smaller and individual leaf damage more significant, knock colonies off with a strong jet of water from a hose, directing it at the undersides of leaflets. Horticultural soap spray applied to the undersides of affected leaves provides effective and bee-safe control. Avoid broad-spectrum insecticides, which eliminate the predators that provide long-term regulation.
2. Late frost damage
Aralia produces its leaves later in spring than most deciduous trees, typically in late May or early June, which means it often avoids the worst late frosts. However, in seasons with unusually late frosts or in gardens in cold, north-facing positions, the emerging foliage can be caught. The large, soft leaflets are extremely frost-tender and even a light frost is sufficient to cause significant damage.
What to look for
Leaflets blacken, wilt, and collapse following an overnight frost, sometimes dramatically, hanging limply from the leaf stalks. The damage appears suddenly and is typically most severe on the outermost growth and the topmost emerging leaves. The blackened tissue has an initially water-soaked appearance before drying to a papery brown. Unlike drought damage, which develops over days, frost damage appears overnight. New growth should emerge from the stem within two to four weeks, as aralia has strong regenerative capacity from its thick stems and extensive root system.
What to do
Do not prune frost-damaged aralia immediately; the dead material provides some protection for the buds and developing tissue beneath. Wait until you can see new growth beginning to emerge from the stems and then cut back to just above a healthy swelling bud. On young plants, covering with horticultural fleece during any forecast frosts in late May or early June gives effective protection. Choose a planting position that avoids the worst frost pockets: a sheltered, south-facing spot with good cold-air drainage, rather than a hollow or north-facing enclosed position.
3. Drought stress
Aralia elata grows naturally in moist, fertile soils at the edges of deciduous woodland in Japan, Korea, and north-east China. Despite its appearance as a tough, low-maintenance statement plant, it is susceptible to drought stress, particularly in its first few years before its root system spreads sufficiently to access deep soil moisture. The enormous combined surface area of its compound leaves means water loss through transpiration is high.
What to look for
Leaflets at the tips and margins of the compound leaves turn brown and papery, curling inward. In prolonged drought the entire canopy may droop and the tree can drop its leaves entirely before the normal autumn leaf fall. The browning has a tan, papery quality rather than the black or dark brown of frost damage, and develops over days rather than overnight. The soil beneath the tree feels very dry even at depth. Suckering may increase as a drought stress response, with the root system producing more stems in an attempt to regenerate.
What to do
Water young aralia deeply once or twice a week during any dry spell in their first three years. Apply a generous mulch of well-rotted garden compost or bark chip 100 mm deep across the root zone to conserve moisture. Established plants are more drought-tolerant once their root system extends widely, but benefit from watering during prolonged dry spells of three weeks or more. Improve moisture retention in sandy or free-draining soils by incorporating large amounts of organic matter before planting.
4. Waterlogged soil
Aralia requires moist, fertile, well-drained soil and does not perform well in waterlogged or compacted conditions. Extended waterlogging causes root death and prevents effective uptake of water and nutrients, leading to yellowing, wilting, and leaf curl despite the soil appearing wet. The problem is particularly common on heavy clay soils during wet winters.
What to look for
The plant looks poorly despite adequate moisture. Leaves yellow and the leaflets curl and wilt even when the soil is not dry. New growth is weak and pale, and the overall plant may look increasingly sparse over successive growing seasons. The suckering habit may become more pronounced as the plant attempts to regenerate around the stressed parent. Digging carefully around the root zone reveals dark, rotten roots rather than healthy pale ones.
What to do
Improve drainage before planting. On clay soils, incorporate coarse grit and organic matter and consider planting on a slight mound to raise the root zone. Avoid positions where water collects or stands after rain. If an established plant is suffering in a poorly drained position, consider moving it in early spring, retaining as much of the root ball as possible. Aralia transplants reasonably well when handled carefully and moved at the right time.
5. Root disturbance
Aralia is highly sensitive to root disturbance. Digging, cultivating, or severing roots near the base of the plant causes an immediate stress response that manifests as wilting, leaf curl, and sometimes sudden leaf drop across much of the canopy. Paradoxically, root damage also triggers excessive suckering as the plant responds to perceived damage by attempting to regenerate.
What to look for
Wilting and leaf curl appear suddenly following any digging, planting, or ground works near the tree. The onset is rapid, often within a day or two of the disturbance. Multiple new suckers may appear in the weeks following root damage, sometimes emerging at considerable distances from the parent plant. Unlike other causes of leaf curl, root disturbance has a clear temporal connection to a physical event rather than to weather conditions.
What to do
Avoid any cultivation or digging within the root zone of established aralia, which typically extends to the full spread of the canopy and often beyond. Do not plant other subjects within this zone as digging for their establishment will damage aralia roots. If planting near an established aralia is unavoidable, use plug plants or bare-root subjects planted with minimal soil disturbance. After any unavoidable root damage, water the plant deeply and mulch the root zone to reduce additional stress while it recovers. Most plants recover from mild root disturbance within a growing season.
Frequently asked questions
Is aralia invasive in the UK?
Aralia elata (Japanese angelica tree) spreads aggressively by root suckers, which can emerge several metres from the parent plant. This suckering habit makes it potentially invasive in garden settings, particularly in fertile, moist soils. It is not listed as an invasive species in the UK but should be planted with this habit in mind, and suckers should be pulled out or cut off at ground level promptly before they establish. Remove suckers by pulling rather than cutting where possible, as cutting stimulates more suckering.
How do I stop aralia from spreading?
The most effective way to limit aralia's spread by suckering is to install a physical root barrier around the planting area at the time of planting. Use a heavy-duty polyethylene root barrier at least 60 cm deep. Inspect the area around the plant regularly in spring and summer and remove any suckers as soon as they appear, pulling them away from the root rather than cutting. Keeping the soil around aralia drier and less fertile than it would prefer also reduces vigorous suckering.
Why are my aralia leaves dropping in summer?
Sudden summer leaf drop on aralia is most commonly caused by severe aphid infestation, drought stress, or damage to the root system from digging or cultivation near the trunk. Aralia produces its entire huge canopy of compound leaves very quickly in late spring, and stress at any point in the growing season can trigger early leaf drop. Waterlogging is another cause; aralia needs well-drained soil despite its preference for moisture.
When does aralia flower?
Aralia elata flowers in late summer, typically July to September in the UK, producing large, flat-topped heads of small cream-white flowers held above the extraordinary canopy of large compound leaves. The flowers are attractive to bees and butterflies and are followed by small purple-black berries in autumn. The combination of spectacular foliage, late-season flowers, and autumn fruit makes aralia one of the most ornamentally interesting plants for the summer garden.
Does aralia have sharp thorns?
Yes. Aralia elata and Aralia spinosa both have sharp, prominent spines on their stems, branches, and often on the leaf stalks. These spines can cause painful puncture wounds and make pruning and working around the plant uncomfortable without protective gloves and clothing. The spines are one reason for siting aralia where children and pets will not regularly brush against it. The cultivar 'Silver Umbrella' (syn. 'Variegata') has the same spiny character but with ornamental variegated foliage.
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