Paulownia Leaves Curling
Frost damage and drought stress are the most common reasons paulownia leaves curl. This guide shows you how to identify each cause and keep your empress tree producing its spectacular foliage.
1. Frost damage
Frost damage is the single most common cause of sudden leaf collapse and curling on paulownia in the UK. The tree's enormous leaves emerge very quickly in late spring and are among the softest and most frost-tender of any hardy garden plant. Even a mild late frost of minus 1 to minus 2 Celsius is sufficient to destroy the leaves overnight, sometimes within hours of them looking perfectly healthy.
What to look for
Leaves blacken, wilt, and curl dramatically, often collapsing completely and hanging limply from the stems. The damage appears very suddenly, typically overnight following a late frost. The leaves may smell slightly of cooked vegetation as cell damage occurs. If you look closely at the main stem and any secondary shoots, you will usually see dormant buds that have not yet broken; these will regenerate the plant. Frost damage should not be confused with drought, which develops more slowly and does not cause the characteristic blackening.
What to do
Do not prune frost-damaged paulownia immediately. The dead leaves protect the buds and stems beneath from further cold. Wait until mid-May or until you are confident that further frosts will not occur, then cut back to just above where you can see live green buds emerging. The regrowth from paulownia is exceptionally fast and vigorous; plants often produce impressive new leaves within a few weeks of pruning. In future years, protect young plants with horticultural fleece on nights when frost is forecast in late April and May, and choose a planting position against a sheltered south-facing wall if late frosts are a regular occurrence in your garden.
2. Drought stress
The leaves of paulownia, which can reach 60 cm or more across on vigorous coppiced growth, have an enormous surface area and lose water through transpiration at a very high rate. In dry or hot conditions, the plant can lose water faster than its roots can supply it, causing the leaves to wilt and curl within hours of conditions becoming stressful.
What to look for
Leaves droop and curl inward along the midrib. On large coppiced specimens the entire canopy may droop dramatically in the afternoon heat. The curl is usually reversible overnight if the stress is mild, with leaves recovering their full extent by morning. In prolonged drought the leaf margins turn brown and papery. Young plants in their first year are most at risk; established paulownias in the ground develop extensive root systems that access deep soil moisture and are much more resilient.
What to do
Water young paulownia trees deeply once or twice a week during dry spells in their first two or three years. For coppiced specimens grown primarily for their foliage, keep the root zone consistently moist throughout the growing season; the enormous transpiring leaf area means water demand is far higher than for a normal-sized garden tree. Mulch the root zone with a generous layer of wood chip to conserve soil moisture. In a heatwave, temporary shade cloth over a young plant can dramatically reduce leaf wilting and water loss without reducing the plant's growth.
3. Wind scorch
The huge, velvety leaves of paulownia are extremely vulnerable to damage from strong or persistent wind. Even moderate wind can cause the leaf margins to brown and curl on exposed plants, and a strong storm can tear leaves apart or shred them entirely. This is one of the reasons paulownia performs best in sheltered garden positions.
What to look for
Leaf margins brown and turn papery, particularly on the side facing the prevailing wind direction. Leaves curl downward at the edges as the damaged tissue dries and contracts. Unlike frost damage, which is sudden and uniform across the whole canopy, wind scorch tends to be progressive and affects the windward side first. Leaves may also be physically torn along veins or at the petiole junction in very strong winds.
What to do
Plant paulownia in a sheltered position protected from prevailing winds. A south-facing spot against a wall or fence, or in the lee of other large shrubs or trees, suits it well. In an exposed garden, erect a temporary windbreak of permeable mesh around young plants in their first two or three years while they establish. Do not use a solid barrier, which causes turbulence. On established plants, accept some wind damage as unavoidable or move to coppicing to limit the height and therefore wind exposure.
4. Powdery mildew
Powdery mildew can affect paulownia in warm, dry summers, particularly on plants in sheltered positions where air circulation around the large leaves is restricted. The infection is usually more of a cosmetic issue than a serious threat, but on plants grown primarily for their dramatic foliage it can reduce the ornamental impact significantly.
What to look for
A white or grey powdery coating develops on the upper and sometimes lower surface of leaves, particularly on the newest growth. Affected leaves curl upward at the margins and may feel slightly papery. On the large, hairy leaves of paulownia, the mildew can be confused with the natural greyish velvety surface; look for a uniformly distributed white powder that can be rubbed off rather than the texture of the leaf surface itself.
What to do
Remove and bin heavily affected leaves. Improve air circulation around the plant. Avoid overhead watering and water in the morning so that any wet foliage dries during the day. A fortnightly spray of diluted milk solution (one part whole milk to nine parts water) is an effective and safe treatment. On coppiced plants, ensure that the single vigorous stem is not producing growth so dense that the leaves are pressed against each other. Feed with a balanced rather than high-nitrogen fertiliser to avoid producing overly soft, susceptible growth.
5. Aphids
Aphids are not a major pest of paulownia but will colonise the soft new growth that the plant produces, particularly following coppicing. The enormous leaves and vigorous growth mean that aphid damage is rarely visually significant, but on young plants or those under other stress it can compound existing problems.
What to look for
Young leaves at the shoot tip curl and crinkle. Part the curled tissue to find pale green or yellowish aphids feeding on the undersides. Honeydew deposits on the leaf surface below aphid colonies lead to black sooty mould. On paulownia the very large leaf size means even a substantial aphid colony may look insignificant against the overall plant, but the honeydew fall can be considerable and may coat objects below.
What to do
On established plants, aphid infestations are self-limiting and natural predators will control them without intervention. On young or stressed plants, knock colonies off with a strong jet of water or spray with horticultural soap solution. Avoid broad-spectrum insecticides that destroy the natural predator populations which provide long-term control. Keeping the plant in vigorous health through appropriate feeding, watering, and mulching is the best defence against significant aphid damage.
Frequently asked questions
Why did my paulownia leaves blacken and curl after looking fine?
Sudden blackening and curling of paulownia leaves in spring is caused by a late frost. The huge soft leaves that emerge in late spring are extremely frost-tender; even a light frost of minus 1 or 2 Celsius can blacken them overnight. The plant almost always regrows from the stem or base: do not prune until you can see where new growth is emerging.
How do I get the biggest leaves on my paulownia?
To produce enormous leaves (sometimes exceeding 60 cm across), cut the paulownia back hard to near ground level each spring before growth begins. This coppicing technique forces all the plant's energy into one or two vigorous new shoots, which produce leaves far larger than those on an uncoppiced tree. Combine with generous watering and a high-potassium feed for best results.
Will my paulownia recover from frost damage?
Yes, almost certainly. Paulownia regrows vigorously from the base, from the trunk, or from any surviving live wood after frost. Do not prune frost-damaged growth until mid-May to be sure there are no further frosts, then cut back to where you can see new green buds or shoots emerging. The regrowth is often so fast and vigorous that the plant looks better by August than it did before.
Is paulownia invasive in the UK?
Paulownia tomentosa can self-seed in warmer parts of the UK and is considered invasive in parts of continental Europe and North America where summers are hotter. In the UK's cooler climate it sets seed less reliably, but it is worth deadheading flowers to be cautious. It spreads vigorously from roots and stumps but does not naturalise as aggressively in the UK as in warmer regions.
Why is my paulownia not producing flowers?
Paulownia flower buds form in autumn and overwinter on the plant, opening before the leaves in spring. A hard winter frost destroys these buds, preventing flowering even when the plant itself survives. Additionally, plants that are coppiced annually for foliage effect will never flower, as they never develop the mature wood needed for bud formation. Allow a stem to grow for two or more years without cutting to encourage flowers.
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