Did you discover your prize tomato plants looking like their leaves are turning into crispy claws? After years of helping countless gardeners troubleshoot their tomato troubles, I’m here as the gardening expert to help reassure you and provide the fix for curling tomato leaves in the greenhouse or if your tomatoes are planted outside.
Whether you’re dealing with a few suspicious curled leaves or an entire greenhouse that looks like it’s been hit by a botanical tornado, this guide will help you understand exactly what’s happening to your tomato plants and how to get those leaves back to their healthy, flat state so you can concentrate on harvesting fantastic tomatoes in summer.
Your tomato’s curling leaves aren’t necessarily a sign of disaster. These curled leaves are actually your plant’s way of communicating stress, and most causes are entirely fixable once you know what to look for. From heat stress and inconsistent watering to aphid invasions and the dreaded tomato leaf curl virus, I’ll guide you through the most common culprits and provide you with practical, tried-and-tested solutions. By the end of this guide, you’ll know exactly how to diagnose your plant’s problem and prevent future curling catastrophes.
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Tomato leaf curling, whilst alarming to gardeners, can stem from several interconnected factors. Understanding these causes is crucial because the solution depends entirely on accurate diagnosis; treating the wrong problem can actually make things worse for your struggling plants. I always like to spend a few minutes looking not just at the problem plant but the environment, what’s going on around and looking at all conditions first.
Most tomato leaf curling falls into six main categories:
The key is learning to read the subtle differences in how curling presents itself, as each cause creates distinct patterns, timing, and accompanying symptoms.
Unlike many houseplant problems, tomato leaf curling often develops in response to outdoor environmental factors that can change rapidly. This actually works in your favour for most causes; once you identify and correct the problem, improvement can be surprisingly quick.
Your tomato’s curling pattern tells a detailed story. Upward curling (leaves cupping skyward) typically indicates heat stress or overwatering. Downward curling suggests underwatering or pest damage. Rolling from the edges inward points to environmental stress. Twisting combined with yellowing indicates viral problems.
Understanding your plant’s normal growth helps you spot problems early. Healthy tomato leaves should be flat, green, and slightly fuzzy to the touch. Any deviation from this normal appearance, whether curling, twisting, or unusual colouration, indicates your plant needs attention.
Only remove severely damaged, yellowing, crispy or dried curled leaves to improve air circulation and prevent them from becoming disease entry points. Cut cleanly at the stem junction using sterilised secateurs.
However, if the leaves are simply curled but still green, not crispy and healthy-looking, treat the underlying cause first. These leaves often recover once environmental conditions improve, and removing too much foliage can cause further stress to the plant.
Environmental stress is the most common cause of tomato leaf curling, accounting for approximately 60% of the cases I encounter. This includes heat stress, wind damage, and sudden changes in humidity that cause plants to curl their leaves as a protective mechanism.
A new gardener emailed me last year whose greenhouse tomatoes had suddenly developed severe leaf curl overnight. It turns out their automatic vent opener had failed during a heatwave, creating an oven-like environment. Once I advised them to increase ventilation and provide the plants with temporary shade, the new growth emerged perfectly flat within a week.
Tomatoes evolved in moderate climates and struggle when temperatures consistently exceed 30°C or drop below 10°C. When stressed, they curl their leaves to reduce surface area exposed to harsh conditions, essentially creating their own ‘micro shade’ and reducing further water loss.
This protective mechanism becomes problematic when environmental stress persists for extended periods, as the plant diverts energy from fruit production to survival mode, resulting in large amounts of leaves curling inwards.
Environmental stress curling typically affects the entire plant rather than isolated areas. The curling usually presents as upward cupping during heat stress or tight rolling during wind stress, often accompanied by slightly pale or bronzed leaf colouration.
Check your growing conditions during the hottest parts of the day. Greenhouse temperatures above 32°C, strong winds, or dramatic day/night temperature swings all trigger stress responses in tomato plants.
Look for these additional environmental indicators that things are too hot in your greenhouse:
Provide immediate relief through temporary shade cloth (30-40% shade) during extreme heat, improve ventilation in greenhouses with additional vents or fans, and create windbreaks for outdoor plants exposed to strong winds.
For greenhouse growers, install automatic vent openers if you don’t already have them, and consider adding shade paint to glass during the summer months. Outdoor growers should position plants in locations protected from strong prevailing winds. I like to leave my greenhouse door fully open on hot days and pour a bucketful of cold water on the floor to help raise humidity.
Monitor temperatures closely during heat waves and be prepared to provide emergency shade during extreme conditions. Even temporary solutions like old bedsheets thrown over the top of your greenhouse can save your crop during unexpected temperature spikes.
If you struggle year on year with tomato leaf curl, it may be time to invest in automatic irrigation systems, permanent shade structures, or cold frames that you can move tomatoes to to stop them getting too hot.
Also consider your garden’s microclimate when positioning tomato plants, ie the aspect it faces and which parts trap the sun. South-facing walls create heat traps that may be too intense, whilst exposed positions may subject plants to excessive wind stress.
Inconsistent watering ranks as the second most common cause of tomato leaf curling, with both overwatering and underwatering capable of triggering curling responses. Tomatoes require consistent moisture levels to maintain proper cellular pressure and leaf structure. A lot of new gardeners think they are watering when really they are just ‘sprinkling’.
The biggest problem I see time and time again is people watering daily but only giving tiny amounts to each plant. Death by a thousand sprinkles, I sometimes call it. This surface watering of micro amounts simply evaporates and never gets into the main root system of the tomatoes, and can trick new gardeners, in particular, into thinking they are watering their plants, when in reality, it’s not. This is why I’m always trying to teach Ninjas that thorough watering using soaking, less frequently than daily sprinkles, is the best option.
Tomatoes need soaking a couple of times a week and sometimes daily in heatwaves or in the peak of the growing season. Tomatoes are thirsty plants!
Overwatering creates equally problematic curling as roots become waterlogged and unable to function properly. The leaves curl upward as the plant struggles to process excess moisture and maintain proper cellular function. You can usually tell this as the soil starts to smell eggy or ‘off’ as anaerobic conditions appear (lack of oxygen in the soil).
Underwatering causes downward curling as leaves attempt to conserve moisture and reduce surface area exposed to evaporation. This protective response becomes permanent if water stress continues.
Overwatering typically causes curling, which is characterised by upward cupping combined with yellowing lower leaves, slow growth, and possibly fungal issues in the soil (look for a sudden outbreak of mushrooms or fibre-like fungus on the grow bag’s surface). The plant may appear generally unhealthy despite adequate moisture.
Underwatering curling presents as downward rolling or folding, often accompanied by wilting during the hottest parts of the day. Leaves may feel crisp or papery to the touch, and growth slows dramatically.
Check soil moisture by inserting your finger 5-7 centimetres deep. Properly watered tomato soil should feel evenly moist but not waterlogged, with clear wet and dry cycles.
For overwatered plants, immediately reduce watering frequency and empty any trays or saucers that the plants are on. Let them breathe for a day or two.
For underwatered plants, begin deep, thorough watering sessions that saturate the entire root zone. Water the soil slowly to allow proper penetration, rather than flooding the surface and only stop once its saturated and the water starts to run out the bottom of the container or grow bag.
Establish consistent watering routines based on soil moisture rather than calendar schedules. Tomatoes typically need watering every 2-3 days in hot weather, less frequently in cool conditions. A finger in the soil usually tells you if it’s bone dry or moist. Use your common sense, Ninjas!
If you’re away with work or on holiday, then consider installing drip irrigation or soaker hoses for consistent watering. These systems reduce water waste and provide steady hydration that prevents stress-induced curling, great if you’re off to Spain for two weeks in the middle of the summer holidays!
Mulch around plants with organic materials to retain soil moisture and reduce the frequency of watering. Straw, compost, shredded leaves, or shredded newspaper all work excellently for tomato plants.
Monitor weather conditions and adjust watering accordingly. Hot, windy days increase water consumption, whilst cool, humid conditions reduce plant water needs. As I mentioned earlier, it’s common sense once you know!
I’ts time to talk about pesky greenhouse and garden pests as a potential vector for tomato leaf curling issues. Whilst Garden Ninjas’ approach is to live and let live in the garden, sometimes organic pest solutions are needed to keep the balance. Especially in a close environment like a greenhouse, where ladybirds, predatory wasps, or birds can’t easily enter to help pick off juicy bugs, as they would in an open garden.
Several common pests can cause tomato leaf curling, with aphids, whiteflies, and spider mites being the primary culprits. These tiny insects weaken plants by feeding on plant juices and can transmit viral diseases that cause additional curling problems.
Aphid infestations often go unnoticed until curling becomes severe, as these small insects cluster on leaf undersides and new growth tips. Their feeding disrupts normal leaf development and can introduce viral diseases.
Whiteflies create similar damage patterns and are particularly problematic in greenhouse environments where they can reproduce rapidly. Their feeding causes leaves to curl upward and may be accompanied by sticky honeydew deposits.
We’ve all been there when one day all your plants look healthy in the greenhouse and then the next there is an outbreak of pests or critters attacking your plants! Pest-related curling often affects new growth first, as soft young leaves are preferred feeding sites. Look for small insects on leaf undersides, sticky honeydew deposits, or tiny stippling marks where insects have fed. Spotting pests quickly is key to avoiding leaf curl.
Aphid damage typically shows as downward curling combined with stunted growth and distorted new leaves. Heavy infestations may cause yellowing and general plant decline.
Whitefly damage appears as upward curling with possible silvering or yellowing of affected leaves. Adults flutter around plants when disturbed, making identification easier. The easiest way is to look closely and see if any pests are lurking, usually on the underside of your tomato leaves.
Begin treatment immediately upon discovering pests, as populations can explode rapidly in favourable conditions. Start with gentle solutions, such as strong water sprays, to physically dislodge insects, which can be fun to swipe them off the plants without reaching for the pesticides or chemicals.
Apply one of my homemade pest treatments you can make yourself, and allow Mother Nature to do the rest. Avoid neem oils, shop-bought pesticides and other instant ‘bug blasters’, they cause far more harm to the environment than you would expect.
One of the biggest niggles I have with the horticulture industry is the overselling of plant feeds, fertilisers and supplements. For the beginner gardener, these feeds can seem like a must-have for great harvests, but overfeeding is just as bad for plants as neglect! Most fruiting plants need far less plant food than you think, and constantly ydrenching them in nitrogen, potassium and phosphorus to try and get more produce can sometimes be the cause of plant illness! Tomatoes are the one fruit that does require regular feeding, but of very specific tomato liquid fed that’s potassium-rich.
Nutrient imbalances, particularly excess nitrogen or potassium deficiency, can trigger tomato leaf curling. Overfertilised plants often show upward leaf curling as they struggle to process excessive nutrients, whilst deficient plants may curl leaves to conserve resources.
Excess nitrogen creates lush, soft growth that’s susceptible to environmental stress and pest problems. The rapid growth outpaces the plant’s ability to maintain proper leaf structure, resulting in curling and distortion. This is why general balanced fertilisers are not suitable for tomatoes; you should always use a high potassium feed instead.
Potassium deficiency causes characteristic leaf edge curling and browning, as this nutrient is essential for proper water regulation and cellular function. Deficient plants struggle to maintain proper leaf turgidity.
Nitrogen excess typically manifests as upward curling, accompanied by very dark green foliage, excessive vegetative growth, and delayed flowering. Plants may appear lush but produce few fruits.
Potassium deficiency causes edge curling, accompanied by yellowing or browning of leaf margins, which often progresses from older leaves to younger ones. Plants may show poor fruit development and increased susceptibility to environmental stress. I use a high-potassium tomato-specific feed like this one to ensure my tomatoes produce large fruits, but not excessive leafy growth.
Calcium deficiency can contribute to curling, combined with blossom end rot in developing fruits. Don’t panic, though, calcium deficiency is rare in my opinion with tomatoes. This often indicates inconsistent watering rather than actual soil calcium deficiency.
For overfertilised plants, firstly, stop feeding the tomatoes completely for two weeks. Water daily to flush the soil with clean water to leach excess nutrients. Resume with diluted fertiliser once plants show signs of recovery, using only a high potassium feed (for fruits).
Address potassium deficiency with balanced tomato fertiliser or organic compost. Avoid high-nitrogen feeds that can exacerbate the imbalance by promoting excessive leafy growth.
Maintain consistent soil moisture, watering every few days heavily, to prevent calcium uptake problems that can contribute to curling and blossom end rot issues.
Tomato leaf curl virus represents the most serious cause of leaf curling, as viral infections cannot be cured and often require plant removal to prevent spread. Several viruses can cause curling, with the tomato yellow leaf curl virus being particularly devastating.
Viral curling typically presents as severe upward rolling, accompanied by yellowing, stunted growth, and poor fruit production. Infected plants rarely recover and often decline rapidly once symptoms appear.
These viruses are commonly spread by whiteflies and aphids, making pest control crucial for prevention. Once established in a garden, viral diseases can persist and infect new plantings. A far cry from the healthy tomtato plant seen below!
Viral curling is usually more severe and persistent than environmental or pest-related curling. Affected leaves exhibit tight rolling that doesn’t improve with environmental changes, accompanied by leaf mottling, and may also result in fruit falling off or starting to rot on the plant.
Viral infections often cause additional symptoms, including:
Remove and destroy infected plants immediately to prevent the spread to healthy plants. Never compost infected material, as some viruses can persist in compost. I can’t stress this enough, as these viruses can spread rapidly throughout your greenhouse and garden.
Choose virus-resistant tomato varieties when available, and purchase plants from reputable sources to minimise the risk of introducing infected tomatoes.
Another top tip is to disinfect tools between plants when working in the garden, as some viruses can spread through contaminated equipment. I use Jayes outdoor cleaning fluid for all my greenhouse cleaning, or a mix of one part bleach to 4 parts water. Dip your tools and blades in this between each plant pruning.
Chemical damage from herbicides, pesticides, or excessive fertiliser applications can cause dramatic leaf curling that mimics other problems. Tomatoes are particularly sensitive to hormone-based herbicides and can show curling from very low exposure levels. Yes, I’m talking to you and your neighbours who may have been using herbicides like glyphosate to kill weeds in your gardens, but got a bit trigger-happy with the sprayer!
Drift from nearby herbicide applications, contaminated compost, or overapplication of weed killers using sprayers can all trigger curling responses. This type of damage often appears suddenl,y a week or so after nearby spray applications.
Chemical curling typically shows as distorted, twisted growth that may affect the entire plant. Recovery depends on the type and amount of chemical exposure. With glyphosate and Roundup, your tomatoes are a gonna Ninjas!
Chemical damage often shows distinctive twisting and curling patterns that look different from environmental or pest damage. New growth may be severely distorted whilst older leaves remain normal. Recent spray applications, new fertiliser use, or exposure to lawn treatments all can indicate chemical causes. When greenhouse doors are left open and neighbours start ‘treating’ their plants and lawns, you can suddenly notice your plants starting to look unhealthy or have leaves curl.
Multiple plants showing similar symptoms simultaneously suggest chemical rather than biological causes, particularly if symptoms appeared suddenly.
Flush affected plants with clean water to dilute and remove chemical residues, and if you see neighbours spraying lawns or plants quickly close your greenhouse doors.
If sprays and herbicides have affected your greenhouse tomatoes, remove severely damaged growth promptly to prevent it from spreading. Recovery time varies depending on the chemical involved and exposure levels. Maybe also have a chat with your neighbours about the drift from spraying pesticides or weed killers, and show them my guides on why we should avoid them!
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For more tomato growing advice and troubleshooting help, explore these helpful resources from the Garden Ninja community:
Whether you’re dealing with leaf curling, blight problems, poor fruiting, or any other tomato challenge, the Garden Ninja community is here to help. Don’t hesitate to ask questions in the forum or browse the extensive library of growing guides!
Rescuing tomatoes with curling leaves is all about accurate diagnosis and responding appropriately rather than panicking at the first sign of distortion. Remember, most curling problems are fixable with the right approach, and these resilient plants can recover beautifully from most issues.
The secret to tomato success? Consistent care beats reactive interventions every time. Stable watering, appropriate feeding, good air circulation, and vigilant pest monitoring prevent most curling problems before they start. Your plants want to produce abundant fruit, so create the right conditions and stay observant!
Each challenge you overcome builds confidence and growing knowledge that benefits your entire vegetable garden. Whether it’s your first curled leaf or nursing severely affected plants back to health, most tomato problems are fixable with patience, proper diagnosis, and consistent care.
Happy Tomato Growing!
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