A houseplant in trouble looks much the same whether it is overwatered, underwatered, sun-scorched, or being eaten quietly by something microscopic. The leaves yellow, droop, brown at the tips. The stem softens. Growth stops. Faced with a list of symptoms that all look alike, most people reach for the wrong intervention first — usually water, often in the direction that makes things worse — and only realise later that they were treating the wrong problem.
This guide is a way out of that. Start with the thing you can see on your plant right now. Each symptom links to the dedicated guide for the underlying cause. By the time you finish reading, you should know which page to open next.
Start with the symptom, not the cure
It is tempting, when a plant looks unwell, to skip straight to a fix — more water, less water, move it, repot it. That impulse is almost always premature. Most of the popular care interventions (especially watering and repotting) are stressors in themselves, and applying them blind can finish off a plant that was otherwise recoverable.
The diagnostic order that works is the one a doctor would use: observe the symptoms, narrow the cause, then treat. Houseplants make this easier than human medicine in one respect — there are only a handful of common causes behind nearly every problem. Once you can read the signs, the right intervention usually becomes obvious.
The symptom map
Find the closest match to what you are seeing. Follow the link to the dedicated guide for that cause. If you would rather work through the diagnosis as a guided sequence of questions, the Plant Symptom Checker is the interactive version of this map — pick your plant, pick what you are seeing, and it routes you to the same destination by a different road.
Yellow leaves
The catch-all symptom. Yellowing can mean overwatering, underwatering, nutrient deficiency, low light, age, or sudden temperature change — and the same plant will yellow differently depending on which leaves are affected and how quickly.
The single most useful piece of information is which leaves are yellowing. Lower leaves yellowing slowly is often natural aging or a slow nutrient shortfall. Lower leaves yellowing quickly, with soil that is wet to the touch, is usually overwatering. Upper or interior leaves yellowing while the lower ones look fine often points to a light or nutrient problem.
→ Yellow leaves — full diagnostic
Brown or crispy leaf tips and edges
This one has a narrow set of causes: low humidity, hard or chemically-treated tap water, fertiliser salt build-up, or — for sensitive species like calatheas and prayer plants — all three at once. It is rarely an emergency, but it is rarely going to fix itself either.
Tip browning that appears slowly and only on the very edges is almost always environmental. Brown patches that appear in the middle of leaves are usually sunburn or fungal.
Drooping or wilting
A plant that has gone soft and limp is asking for either water or oxygen, and telling the two apart is the most important diagnostic skill in houseplant care. Both look identical from above. The deciding factor is the soil: dry soil + wilting = thirsty; wet soil + wilting = drowning.
Watering a wilting plant with wet soil is the most common way that overwatering becomes root rot. If you only remember one rule from this hub, make it this one — always check the soil before you reach for the watering can.
→ Drooping and wilting — what to check first
Leggy, stretched, or pale growth
Stems reaching for the window, exaggerated spacing between leaves, smaller and paler new growth than the older leaves — these are all signs that the plant is not getting enough light to support the size it is trying to be. The plant is doing exactly what it should: stretching toward the strongest available light source, at the cost of compactness and colour.
Leggy growth cannot be undone. What you can do is correct the light going forward, and prune to encourage denser growth from the new conditions. If you are not sure whether the position you have in mind is actually bright enough — UK rooms routinely flatter themselves on this — the Light Calculator will give you a usable estimate from your window orientation, obstructions, and the time of year.
Visible pests — webbing, sticky residue, small moving dots, white fluff
Houseplant pests are usually invisible until you go looking for them. Once they are visible, the infestation has often been running for weeks. The good news is that the same six or seven pests cause nearly all problems on UK houseplants, and the treatment protocols are well-understood and effective if applied consistently.
The most common visible signs: fine white webbing between stems (spider mites), sticky honeydew on leaves or the surfaces below (most sap-sucking pests), small flies near the soil (fungus gnats), or white cottony patches in leaf joints (mealybugs).
→ Pest identification and treatment
Sudden collapse, soft stem, sour smell from the soil
If a plant has gone from looking healthy to suddenly drooping with a stem that feels soft at the base — and especially if the compost smells sour or swampy — the most likely cause is root rot. By the time these symptoms reach the surface, the root system has usually been failing for some time.
Acting quickly matters. The treatment is straightforward but unforgiving: remove the plant from its pot, wash the roots, cut away every soft brown root, and repot into fresh free-draining compost. Half-measures rarely work.
→ Root rot: identify, treat, prevent
White or rusty crust on the soil surface
The crust is usually a build-up of mineral salts from tap water or fertiliser, or, less commonly, a harmless saprophytic mould. Neither will kill a plant directly, but salt build-up does change soil chemistry over time and contributes to root tip damage. The fix is straightforward: scrape off the visible crust, flush the pot with two pot-volumes of soft water (rain water or filtered), and let it drain fully. Plan to repot if it returns within a month.
If the crust is fluffy and white rather than crusty and crystalline, suspect a fungal bloom from over-moist soil — let the surface dry out fully between waterings and increase airflow around the plant.
The mystery: something is wrong but I cannot say what
This is the most common reason people open a guide like this one. The plant looks slightly off. Growth has slowed. It does not look ill exactly, but it does not look right.
In this case, work through the watering guide and light guide first. The overwhelming majority of “slow decline” cases are environmental — the plant is getting too much water, too little light, or both. The Plant Symptom Checker is also worth a pass for these: working through a structured set of questions sometimes surfaces a symptom you had stopped registering as a symptom. Adjusting either water or light takes weeks to show results, so be patient with your fix. If both have been correct for over a month and the plant has continued to deteriorate, suspect a slow root problem and check the root ball.
The meta-rule: when in doubt, check the roots
If you take only one diagnostic move away from this page, take this one. The roots tell you more about a plant’s actual condition than any number of above-ground symptoms — and almost no one looks at them until the plant is past saving.
Gently lift the plant from its pot. Healthy roots are white or pale tan, firm to the touch, and plentiful. They smell faintly of fresh soil. Brown, soft, or sparse roots tell you that the foundation of the plant is failing, regardless of what the leaves are doing. A plant with healthy roots will almost always pull through whatever is troubling it above-ground. A plant with rotting roots needs intervention now.
This check takes thirty seconds. Do it before you reach for any other treatment.
Three diagnostic moves before you Google
Before assuming the worst — or applying any fix — try these three in order. Most problems resolve at one of these three steps without further intervention.
1. Check the soil with your finger, not your eyes. The surface of a pot can look bone-dry while the centre is still saturated, or vice versa. Push a finger one to two inches in. Wet, damp, or dry tells you which way to lean.
2. Look at the plant against its light. Walk around the room. Is the plant getting genuine usable light, or is it sitting in what feels bright but is actually dim by the standards of the species? UK rooms are often dimmer than they feel, especially in winter and in north-facing positions. The Light Calculator takes thirty seconds and replaces guesswork with a number.
3. Lift the pot. A wet pot feels heavy and a dry one feels light. After lifting your plants a few times you will start to know the feel of a pot at the moment it needs water — better than any schedule.
When a plant cannot be saved
Sometimes the answer is that the plant is past saving, and recognising this kindly is a skill of its own. Severe root rot that has reached the crown, a stem that has gone soft and brown at the base, or a plant with no remaining healthy tissue — these are not always recoverable, and forcing a recovery rarely helps anyone.
If you are facing this, look for what can be saved. A stem cutting from healthy upper growth, propagated in water or fresh compost, often outlives the parent. For aroids, vining species, and many succulents, the cutting is the plant — the original root system was always going to be replaced eventually. See the propagation guides for stem cuttings, water propagation, and division for the technique that fits your species.
A plant that ends in cuttings is not a failure. It is a continuation.
A note on patience
The instinct, when a plant looks unwell, is to do something — change pot, change soil, water more, water less, move it twice in a week. Almost all of these things stress the plant further, and most of them stress it more than the original problem was going to.
The diagnostic order is: observe, identify, correct one thing, wait. Plants respond to changes on a timescale of weeks, not days. A single correct adjustment, held steady for a month, will outperform five interventions in a fortnight every time. The patience part is the hard part. It is also the part that works.
If you have the diagnosis right, you are most of the way there. Open the linked guide, follow the protocol, and give the plant the time it needs.
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