Lentils are one of the oldest cultivated crops on earth and an increasingly popular choice for UK allotment gardeners and smallholders who want to grow their own pulses. The plants are small and undemanding, the harvest rewarding, and a bag of home-grown Puy or Beluga lentils on the kitchen shelf is genuinely satisfying. But they are also delicate. The tiny pinnate leaves and slender stems are vulnerable to aphids, and the plants are susceptible to Ascochyta blight, the most significant lentil disease worldwide. When those small leaves start to curl, you need to diagnose the cause quickly. The season is short, running from a March to May sow to an August to September harvest, and a badly affected plant will not recover in time to produce a useful crop.
Lentils in the UK: what you are working with
Lens culinaris is a small erect annual growing to around 20 to 45 centimetres. The leaves are true pinnate structures, composed of several pairs of small oval leaflets that give the plant a light, feathery appearance quite unlike the broad foliage of a runner bean or brassica. Small white or pale lilac flowers appear from late spring into early summer, followed by short flat pods each containing one or two lentil seeds. The plants are delicate and should be handled carefully when inspecting for pests or disease.
The main varieties grown in the UK include Masoor (the source of red and pink lentils, which are actually brown-skinned and only turn red when split and cooked), Puy-type (small, speckled, and dark green, holding their shape when cooked), Beluga (very small, black, and firm), and Castelluccio, an Italian heritage variety with a fine flavour. All are suitable for UK growing in a sunny, sheltered position in well-drained soil, but they perform most reliably in South and East England where summers are warmer and drier.
Sow direct into well-prepared, free-draining soil from March to May, after the last hard frosts. Thin seedlings to around 10 to 15 centimetres apart. Lentils need moisture for germination and during the early weeks of growth, but once established they are genuinely drought-tolerant and in fact prefer drier conditions for good pod development. Harvest in August to September when the lower pods begin to dry and rattle. Crop rotation is important: move lentils to a fresh bed every year and aim for at least a three to four year gap before returning to the same ground.
Cause 1: Aphid infestation
Pea aphid (Acyrthosiphon pisum) and related species are the most common pest on lentils in the UK and the first thing to investigate when leaves start curling. Pea aphids are larger than common greenfly, ranging from pale to mid green or pinkish-green, and they congregate in dense colonies at the soft growing tips and on the undersides of the tiny pinnate leaflets. The colonies are often visible from a short distance as a pale, faintly fluffy-looking mass clustered at the tops of the stems. Their feeding withdraws sap continuously, causing the delicate leaflets to fold and the shoot tip to curl and distort as the plant responds to the sustained stress. Heavily infested plants slow or stop producing new growth entirely.
The secondary signs of aphid activity are reliable even before you see the insects themselves. Look for a shiny, sticky coating of honeydew on the stems and leaves below the active colonies, and for black sooty mould growing on top of the honeydew deposits. Ants moving purposefully up and down the stems are another indicator: ants farm aphid colonies for honeydew, and their presence on lentil stems usually confirms an established infestation above. The small scale of the lentil plant compared to a bean or pea means that even a moderate-sized aphid colony represents a proportionally significant drain on the plant.
Beyond the direct physical damage, aphids on lentils pose a risk as vectors of aphid-transmitted mosaic viruses. This makes early control genuinely important rather than merely cosmetic. A colony that has been present and reproducing for a week before it is noticed has had time to build to a size at which virus transmission risk becomes significant.
Controlling aphids on lentils
Because lentil stems and leaflets are small and fragile, be careful when treating. A firm but not forceful jet of water directed at the colonies is the most practical first response: get underneath the shoot tips and target the undersides of the leaflets where the main feeding mass sits. Repeat every two to three days. For larger colonies, insecticidal soap sprayed directly onto the affected growth is effective and breaks down rapidly once dry, leaving no lasting residue. Where a shoot tip is heavily infested and visibly distorted or withered, removing it entirely takes out the densest concentration of insects and the most damaged tissue in one action. Natural predators including ladybirds, hoverfly larvae, and parasitic wasps provide effective season-long control on well-managed plots where broad-spectrum pesticides are not used, and on a small allotment bed these can keep aphid populations below damaging levels without any intervention at all in many seasons.
Cause 2: Ascochyta blight
Ascochyta blight, caused by the Ascochyta lentis fungal complex, is the most significant disease of lentil worldwide and the cause most likely to result in complete crop loss on a UK plot. It thrives in the cool wet conditions that parts of the UK experience in spring and early summer, and a wet year with repeated rain events can spread it rapidly through a whole bed of plants within a few weeks. The disease is seed-borne as well as soil-borne and airborne, which is why starting with certified disease-free seed is so important.
The symptoms are distinctive once you know what to look for. Oval or elongated brown or tan lesions appear on the leaflets, with a slightly darker brown border around a paler centre. The affected leaves curl at the margins, yellow progressively, and die as the lesions enlarge and coalesce. In severe infections the stems develop similar lesions and can collapse entirely. The pods are also vulnerable, developing lesions that allow the fungus to penetrate and infect the seeds inside, which then become the source of next year's problem if saved and resown. The disease spreads through rain splash, so overhead watering or prolonged wet weather dramatically accelerates its progress through a planting.
No chemical treatment is available to home growers for Ascochyta blight. Management relies entirely on cultural controls: using certified disease-free seed, improving airflow between plants by thinning to the recommended spacing, avoiding overhead watering by directing water at the base of the plants, removing and destroying badly affected material rather than composting it, and rotating the crop to a fresh bed every year. A gap of at least three to four years before returning lentils to the same ground is the standard recommendation for reducing soil-borne inoculum to manageable levels.
Other causes of leaf curling on lentils
Drought stress is worth considering on very free-draining soils or during an unusually hot early summer. Lentils are drought-tolerant once established but need consistent moisture during germination and in the first few weeks of growth. In a prolonged dry spell on a sandy or chalky soil, even established plants can suffer moisture stress that causes leaf curl, reduced growth, and early pod abortion. Water during genuinely dry periods, focusing water at the base of the plants. Once pods are forming and swelling, consistent moisture becomes important again for good seed fill.
Waterlogging is the opposite problem but equally damaging. Despite their drought tolerance, lentils die rapidly in persistently waterlogged soil. The roots are extremely sensitive to oxygen deprivation, and a plant sitting in saturated ground will show yellowing leaves, wilting despite wet soil, and rapid decline. Always grow lentils in free-draining soil. If your plot has a heavy clay subsoil or a low-lying area that holds water after rain, lentils are not suited to it without significant improvement to the drainage first.
Powdery mildew can affect lentils in warm dry conditions, typically from mid-summer onwards as the season progresses. A white or pale grey powdery coating appears on the leaf surfaces and causes marginal curling and yellowing. On most UK plots it appears late enough in the season that the crop is already approaching harvest and the impact on yield is limited. Avoid overhead watering, maintain good airflow between plants, and remove affected material promptly.
Virus infection, most commonly from aphid-transmitted mosaic viruses, can cause mosaic mottling and leaf curl on lentils. It is less commonly encountered than aphid or blight problems on UK allotment plots but worth bearing in mind if you are seeing curl and distortion alongside unusual leaf colouring and no obvious pest pressure. Controlling aphids promptly reduces the risk significantly, since aphids are the primary vector.
Prevention: keeping your lentil crop healthy
- Use certified disease-free seed from a reputable supplier. Never save and resow seed from plants that showed Ascochyta blight symptoms.
- Sow in free-draining soil in a sunny, sheltered position. Raised beds or south-facing slopes help in less favourable areas.
- Thin to 10 to 15 centimetres apart to allow good airflow between plants and reduce the microclimate humidity that favours blight.
- Water at the base of the plants, not overhead. Splash from overhead watering carries Ascochyta spores from plant to plant.
- Check shoot tips and leaf undersides regularly from May onwards for aphid colonies. Act early before populations build large enough to stress the plants or transmit viruses.
- Remove and destroy any plant material showing Ascochyta blight lesions. Do not compost it.
- Rotate lentils to a fresh bed every year and aim for a three to four year gap before returning to the same ground.
- Encourage natural aphid predators by avoiding broad-spectrum pesticide use on and around the lentil bed.
Frequently asked questions
Why are my lentil leaves curling?
Pea aphids (Acyrthosiphon pisum) are the most common cause of curling on lentil leaves. Dense colonies form on soft shoot tips and the undersides of the tiny pinnate leaflets, causing them to fold and curl as the plant responds to sap loss. Ascochyta blight is the other serious cause, producing oval brown lesions and causing leaves to curl, yellow, and die as the infection spreads. Check for insects first, then examine the lesions. Drought stress and waterlogging can also cause curling, and powdery mildew produces marginal curl late in the season.
Which UK regions are best for growing lentils?
Lentils perform best in the South and East of England where summers are warmer and drier. They need a long growing season with reliable warmth from late spring through to late summer and do not thrive in cool, wet conditions. Parts of East Anglia, the Thames Valley, and the South East offer the most consistent conditions. Growers in the Midlands and the North can succeed with lentils in sheltered, sunny spots and in warmer-than-average years, but the risk of Ascochyta blight is higher wherever summers are wet and cool, and yields will typically be lower. Puy and Beluga types tend to be the most reliable across a range of UK conditions.
When do I harvest lentils in the UK?
Lentils are ready to harvest in August and September, when the lower pods on the plant start to dry and turn papery and the seeds inside begin to rattle. Do not wait until all pods are dry on the plant, since the early pods will start to split and shed seed. Cut the whole plant at soil level and hang it upside down in a warm, dry, well-ventilated space for two to three weeks to finish drying. Then thresh by beating the bundles against the inside of a large bin or by rubbing the pods between your hands over a sheet. Winnow to separate the seeds from the chaff. Properly dried lentil seed stores for several years.
Can I grow Puy lentils in the UK?
Yes, Puy-type lentils can be grown successfully in the UK in a warm sunny spot in free-draining soil. They are not subject to AOC restrictions when grown outside France, and the flavour of home-grown Puy-type lentils is excellent. The plants perform well in southern and eastern England and are one of the most rewarding pulses to grow from scratch on an allotment or smallholding. Sow from March to May direct into prepared soil, thin to around 10 to 15 centimetres, and harvest in August to September when the lower pods dry and rattle.
Is Ascochyta blight on lentils treatable?
No chemical treatment is available to home growers for Ascochyta blight on lentils. Once a plant shows the characteristic oval brown lesions and yellowing, it cannot be cured. Remove and destroy badly affected plants, avoid overhead watering, and improve airflow between remaining plants to slow the spread. For future seasons, use certified disease-free seed from a reputable supplier, rotate lentils to a fresh bed, and avoid sowing in the same ground more than once every three to four years.