Lathyrus latifolius, the everlasting pea or perennial sweet pea, is one of the most rewarding and low-maintenance climbing plants you can grow in a UK garden. It scrambles up walls, fences, and through shrubs with ease, throws out vivid magenta or white pea flowers from June through to September, and feeds long-tongued bumblebees that depend on it. It is also virtually unkillable once established. But even tough plants run into problems, and curling or distorted leaves are the most common sign that something is wrong. Getting to the right cause quickly means you can act before the flowers are affected.
Why everlasting pea leaves curl: the two main causes
Almost every case of leaf curling on Lathyrus latifolius comes down to one of two things: pea aphid infestations or powdery mildew. Both are very common on this plant in the UK and both tend to peak in warm, dry conditions from June onwards. They look different enough on close inspection that you can tell them apart without specialist knowledge, and both respond well to simple treatment.
Cause 1: Pea aphids
The pea aphid (Acyrthosiphon pisum) is the most likely culprit when everlasting pea leaves curl downwards and inwards at the edges during early summer. Pea aphids are larger than a typical greenfly and distinctly pale, ranging from soft green to pinkish-green depending on the individual. They congregate in loose colonies on the soft growing tips and on the undersides of the broad, wing-shaped leaflets that are characteristic of L. latifolius. Black bean aphids (Aphis fabae) also attack legumes and produce denser, darker clusters, often so thick that the shoot tip beneath them is barely visible. Both species feed by piercing the plant tissue and drawing out sap, and it is this physical damage that causes the leaf margins to roll and the growing tips to distort or stunt.
Pea aphid populations on Lathyrus can become very large during June and July, when colonies build quickly in warm weather. Look for a sticky, shiny coating of honeydew on leaves and stems below the colony, and for black sooty mould growing on top of that honeydew. These are reliable secondary signs that aphids are at work even if you cannot immediately see the insects themselves. On a vigorous, well-established plant the aphid population may cause visible leaf curl without seriously threatening the plant's overall health; the sheer growth rate of L. latifolius in summer often means it puts out enough new growth to stay ahead of moderate infestations.
There is a secondary risk worth knowing about. Pea aphid is a known vector of plant viruses including pea mosaic virus and cucumber mosaic virus. Once a virus is transmitted into the plant, it cannot be removed by treating the aphids. This makes early intervention on aphid colonies worthwhile even when the plant looks otherwise healthy.
How to deal with pea aphids on everlasting pea
A firm jet of water directed at the colonies is the first and most effective non-chemical option. Do this early in the morning and repeat every two or three days. For heavier infestations, insecticidal soap spray applied directly to the colonies is highly effective and breaks down quickly, posing low risk to pollinators once it has dried. Apply in the evening when bees are less active. Avoid broad-spectrum insecticides entirely while the plant is in flower; the long-tongued bumblebees that visit Lathyrus latifolius flowers are among the most important pollinators of the plant and several species depend heavily on it through summer. Natural predators including parasitic wasps, ladybirds, and lacewings typically arrive and reduce populations significantly by late July. Avoiding excessive nitrogen fertiliser keeps new growth firmer and less attractive to aphids.
Cause 2: Powdery mildew
Powdery mildew on everlasting pea is caused by Erysiphe pisi or the closely related E. polygoni, the same fungi responsible for pea powdery mildew in the vegetable garden. It appears as white or pale grey powdery patches on the upper surface of leaves and on stems, and is quite distinct from aphid damage because there are no insects present and the coating is dry rather than sticky. Affected leaves curl, pucker, and yellow at the edges where the fungal growth is thickest. In a bad outbreak the entire plant takes on a dusty, bleached appearance and flower production begins to drop off.
The dense, scrambling growth habit of L. latifolius creates ideal conditions for powdery mildew. The plant climbs to two or three metres and produces a substantial tangle of stems and foliage that restricts airflow in the interior. This sheltered, slightly humid microclimate is exactly what the fungus favours, and the problem is made worse by warm dry spells in late summer when the soil dries out and plants begin to stress. Powdery mildew in the UK is most common from July to September on this plant.
How to deal with powdery mildew on everlasting pea
Remove and bin heavily affected stems and leaves rather than composting them, to reduce the spore load available to spread. Water deeply at the base of the plant during prolonged dry spells; a plant under drought stress is far more susceptible to mildew than one with moist, consistent soil moisture. Avoid watering overhead, which can splash spores and also creates conditions for other fungal problems. Where growth is very congested, cutting back some stems to open up the centre of the plant and improve airflow will slow the spread significantly. A dilute bicarbonate of soda solution (one teaspoon per litre, with a drop of washing-up liquid as a spreader-sticker) sprayed onto affected foliage can help check a mild outbreak. The most effective long-term fix on L. latifolius is also the simplest: cut the whole plant to the ground in late autumn. It will regrow clean and vigorous the following spring with no residual mildew.
Other causes worth knowing
Drought stress is worth considering in a prolonged dry spell, particularly in the first couple of years after planting before the root system is fully established. The large leaf area of L. latifolius transpires heavily in hot weather and, if the roots cannot keep pace with that water loss, the leaves curl and begin to yellow at the margins. A good soak at the base of the plant once or twice a week in very dry conditions is usually enough to prevent this. Once the plant is established, its deep root system makes it genuinely drought-tolerant and watering is rarely necessary.
Viruses including cucumber mosaic virus and pea mosaic virus produce a distinctive mottled or mosaic pattern of yellow and green on the leaves, combined with curling and distortion that does not match the clean downward roll of aphid damage. The mottling is patchy and irregular rather than even, and the leaf surface may pucker or bubble. There is no chemical treatment for a systemic virus infection; the plant should be removed and disposed of (not composted) and aphid populations on nearby plants controlled to reduce the risk of spread.
Slug damage can affect the soft young growth that emerges from the base of the plant in spring, causing ragged edges and distorted early leaves. This is usually temporary and the plant grows through it quickly once stems have hardened off. Leaf spot diseases can cause brown or tan spots with a defined margin; these are rarely serious on an otherwise healthy plant. Late frost on new growth in April or May causes wilted, darkened shoot tips that look alarming but regrow within a week or two.
Prevention: keeping everlasting pea in good health
- Cut the whole plant to the ground each autumn, once the foliage has died back after the first hard frosts. This is the single most important thing you can do for the long-term health of the plant; it removes overwintering sites for aphid eggs and mildew spores and produces clean, vigorous regrowth each spring.
- Water at the base during prolonged dry spells, particularly in the first two years after planting while the root system is developing. Established plants are drought-tolerant but benefit from a deep soak in extreme heat.
- Avoid overhead watering, which can encourage fungal problems and splash soil-borne pathogens onto the lower leaves.
- If growth becomes very congested on a fence or wall, thin out some stems in midsummer to improve airflow through the centre of the plant and reduce powdery mildew risk.
- Watch for aphid colonies in June and July when populations build fastest. Act early with a water jet before colonies become large enough to transmit viruses to healthy growth.
- Resist the urge to use broad-spectrum insecticides while the plant is in flower. Lathyrus latifolius is genuinely important for long-tongued bumblebees; natural predator populations will usually do the work by late summer.
Frequently asked questions
Why are my everlasting pea leaves curling downwards?
Downward curling on Lathyrus latifolius is most often caused by pea aphid (Acyrthosiphon pisum) colonies on the shoot tips and young leaves. Check for soft, pale-green insects clustered at the growing points and on leaf undersides. A firm jet of water or insecticidal soap will clear most infestations. Vigorous plants often outgrow light aphid pressure on their own by late July once parasitic wasps and ladybirds arrive in numbers.
What is the difference between everlasting pea and sweet pea, and do they have the same problems?
Lathyrus latifolius (everlasting pea or perennial sweet pea) and Lathyrus odoratus (annual sweet pea) are closely related members of the legume family and share most of the same problems: pea aphids, powdery mildew, viruses, and drought stress. The key practical differences are that L. latifolius is a perennial that dies back to the root each winter and regrows reliably the following spring, while L. odoratus is grown from seed each year. Everlasting pea flowers are unscented (unlike the famously perfumed annual sweet pea) but the plant is tougher, longer-lived, and requires far less attention once established. If you are expecting annual sweet pea fragrance from L. latifolius, it will not be there, but the plant more than compensates with sheer toughness and months of flower for the bees.
When should I cut everlasting pea back, and will it regrow?
Cut the whole plant to the ground in late autumn, once the foliage has died back or after the first hard frosts. This removes the old stems where powdery mildew spores and pest eggs can overwinter, and encourages fresh, vigorous growth from the base the following spring. Lathyrus latifolius is extremely resilient once established and will regrow reliably from the rootstock year after year. There is no need to dig it up or protect the roots over winter anywhere in the UK.
Can I use pesticides on everlasting pea when it is in flower?
Avoid broad-spectrum insecticides on Lathyrus latifolius while it is in flower, which runs from June to September. The flowers are highly attractive to long-tongued bumblebees, including several species that visit few other garden plants. Insecticidal soap is a safer choice if aphid numbers are severe, since it breaks down quickly and has low toxicity to pollinators once dry. Apply in the evening when bee activity is at its lowest. For light to moderate aphid infestations, a water jet and allowing natural predators to build up is usually enough.
My everlasting pea leaves have a mottled yellow and green pattern and are distorted. What is causing it?
Mottled or mosaic patterning combined with leaf distortion and curling is a classic symptom of a plant virus, most likely cucumber mosaic virus or pea mosaic virus, both of which are spread by aphids. Unlike aphid damage or mildew, viral distortion does not improve after the aphids are removed because the virus is already systemic throughout the plant. There is no chemical treatment. Remove and dispose of affected plants (not in the compost heap) and control aphid populations on remaining plants to reduce the risk of spread to healthy growth nearby.