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Plant care

The rules that sit underneath every species page on this site. A species page tells you what one plant wants; this is the part that does not change from plant to plant, so the species pages do not have to keep repeating it.

It is aroid-shaped. Philodendrons, monsteras and alocasias are what I grow, and that is what the advice assumes, though most of it holds for tropical foliage houseplants generally.

Plants vary and so do rooms. Two people following the same watering rule in different flats are doing quite different things to their plants. Take this as a starting point you then adjust by watching the plant, rather than as a set of instructions.

Light

Bright indirect is the most repeated and least useful phrase in the hobby. What it means in practice: as much light as the plant can get without the sun's disc falling on the leaves for any length of time.

Interior planting work measures light in foot-candles; a lux meter measures the same thing in different units, and one foot-candle is about 10.8 lux. The brackets those guides use run roughly: low light 50 to 250 foot-candles, which is 500 to 2,700 lux, where a plant survives without doing much; medium 250 to 1,000 foot-candles, 2,700 to 10,800 lux, which is where most plants sold as tolerating low light actually live; and bright from about 1,000 foot-candles upwards, which is what bright indirect is reaching for.

For scale, full summer sun outdoors is on the order of 100,000 lux and a well-lit office is a few hundred. That gap tells you the important thing: your eye adapts logarithmically and is a terrible light meter, so a room that feels bright to you can easily be sitting at the bottom of the low bracket.

Phone light-meter apps read the ambient-light sensor beside the front camera. It is uncalibrated, its angular response is poor, and two phones side by side will disagree substantially. That makes an app useful for comparison — this shelf against that shelf, on the same phone, in the same minute, or the same shelf in June and in December — and not useful as an absolute number. If you want the absolute number, a cheap dedicated lux meter is a better twenty pounds.

Distance from the window is a worse model than it looks. The thing that predicts how much light a leaf gets is how much open sky it can see. A plant a metre back from a large unobstructed window with a clear view upward does better than one pressed against a small window that looks at a wall. Light falls off steeply as you move into a room — a position that looks only slightly dimmer usually measures as a fraction. In the northern hemisphere an unobstructed south window is the strongest, east gives gentle direct morning sun that most aroids handle, west gives harsh afternoon sun, and north gives even but weak light.

Duration counts as much as intensity. A meter reading is a snapshot; what the plant lives on is the total accumulated over the day, which greenhouse growers call the daily light integral. Three bright hours and thirteen dark ones is not the same as ten medium hours, even when the peak reading matches.

Getting too much. Pale washed-out patches that go dry, tan or bone-white and sharply outlined, on whichever side faces the sun. A red or bronze cast on some philodendrons. Leaves tilting away from the light or curling along the midrib through the afternoon. The substrate drying very fast.

Getting too little. The gaps between leaves stretching out, each new leaf smaller than the last, fenestration reduced or absent, the whole plant leaning at the window. And the one that gets misdiagnosed: the pot staying wet far longer than it used to, which people then treat as an overwatering problem when the real cause is that the plant is not drinking because it is not working.

A leaf is built for the light it grew in and cannot rebuild itself. Moving a plant out of a dim corner and into a bright window will scorch the leaves it already has, even though the new position is the right one for it. Move it in stages across a week or two and let the new growth arrive acclimatised.

Water

The rule is about the substrate drying, not about the calendar. Everything that sets how fast a pot dries — light, temperature, humidity, air movement, pot material and size, how much root is in it, what the mix is made of — changes through the year and differs between two rooms in the same flat. A fixed interval can only be right for part of that.

Which is why water weekly kills plants. The interval that is roughly correct in July is drowning the plant in December, when it has a third of the light, has more or less stopped growing, and is using a fraction of the water. The people whose plants survive weekly watering are usually the ones quietly skipping it when the pot feels heavy.

Root rot is not caused by water. It is caused by the absence of air. Roots respire, and they take their oxygen from the pores between particles; keep those pores full of water and the roots suffocate, and then the water moulds that are always present — Pythium, Phytophthora and their relatives — colonise tissue that is already dying. That is the whole reason a chunky mix is forgiving: it refills with air quickly.

How to tell a pot is dry, best method first:

  • Weight. Lift the pot right after a thorough watering, and lift it again a few days later. That difference is more reliable than anything else available to you, and it costs nothing.
  • A wooden skewer pushed to the bottom of the pot and left a moment. Damp mix darkens it and clings to it.
  • A finger, to the second knuckle, is about five centimetres — fine as far as it goes, which is not to the bottom of the pot.
  • Not a cheap moisture meter. Those are two dissimilar metals reading conductivity, so they respond to dissolved fertiliser salts as much as to water, and in a bark mix the probe is as likely to be sitting in an air gap as in anything.

For most climbing aroids in a chunky mix: water once the top few centimetres have dried, and before the whole pot has gone bone dry. Alocasia want to stay damper than that and pay for a full dry-out in dropped leaves.

When you do water, water properly — enough that it runs freely out of the drainage holes, and then empty the saucer. A splash that only wets the top leaves dry pockets lower down, never reaches half the roots, and concentrates fertiliser salts in the pot instead of carrying them out of it.

Bottom watering means standing the pot in a few centimetres of water and letting capillarity pull it up, usually over ten to thirty minutes. It genuinely helps in two situations: a coir or peat mix that has dried so far it has turned hydrophobic and now channels water straight down the sides of the root ball, and a fungus gnat problem, since the surface stays dry. Its cost is the exact mirror of top watering's benefit — it never flushes anything out, and salts travel upward with the evaporating water and accumulate at the surface. So bottom water as your routine if you like it, but top water to run-through every few weeks.

A layer of gravel at the bottom of a pot does not improve drainage and slightly worsens it. Water will not cross from a fine layer into a coarse one until the fine layer is saturated, so the gravel raises the saturated zone up into the root ball rather than draining it away from it. Coarser mix and a drainage hole are the things that work.

Water quality matters less than the hobby suggests, for most people and most aroids, and worrying about it is a good way to avoid thinking about the light. It starts to matter when your water is very hard or high in dissolved solids, since the deposits build up in the mix and drift its pH, and that shows up fastest in sphagnum or semi-hydro where there is little to buffer it. It matters if you grow something documented as fluoride-sensitive — that is a short list, mostly Dracaena, Chlorophytum and Cordyline, and among aroids Spathiphyllum, where it produces tip necrosis. Monstera and Philodendron are not on it. And it matters absolutely if your supply runs through an ion-exchange water softener, which trades calcium for sodium and produces water that really is bad for plants; fill from a tap upstream of it.

The standard advice to leave tap water out overnight is advice about chlorine, which does off-gas. Most utilities now disinfect with chloramine instead, which was chosen precisely because it is more stable and does not meaningfully off-gas in a jug on the counter. If you have chloraminated water and a reason to remove it, leaving it to stand is not the method. Rain or reverse-osmosis water is worth the trouble when your tap water is hard and mostly not otherwise — and if you use it, remember it carries no calcium or magnesium, so your feed has to.

Humidity

This is where the hobby and the horticultural literature part company, so it is worth being careful about what is actually known.

The received wisdom is that aroids need 70 to 80 per cent humidity and should be misted daily. What holds up is narrower. The common climbing aroids — Monstera, most Philodendron — grow perfectly well at ordinary indoor humidity, somewhere in the 40 to 60 per cent range. Higher humidity does produce visibly better plants: larger leaves, new leaves that unfurl cleanly instead of sticking and tearing, less crisping at the margins. Growers are not imagining that. But grows better above 60 per cent is a different claim fromneeds 70 per cent, and it is the second one that gets repeated. The plants that genuinely struggle in dry air are the thin, velvety-leaved ones — Philodendron verrucosum, Anthurium crystallinum and their kind — and Alocasia, which in dry air acquires spider mites as a matter of course rather than as a misfortune.

Temperature is missing from all of this. What a leaf experiences is not relative humidity but the gap between the water vapour the air is holding and the amount it could hold, which growers call vapour pressure deficit and which depends on temperature as much as on the humidity reading. Fifty-five per cent at 18 °C is a far gentler environment than fifty-five per cent at 28 °C. It is why the same plant behaves differently in a cool bedroom and a warm living room at an identical hygrometer reading.

Misting does very little, and it is not free. The arithmetic is unforgiving: a few millilitres of water evaporating into a room's worth of air changes the room's relative humidity by an amount you could not measure, and the local effect at the leaf surface is gone within minutes. Against that, the duration of leaf wetness is the standard predictor of infection in plant pathology — bacterial and fungal leaf pathogens need liquid water sitting on the surface for hours in order to get in, and aroids are prone to bacterial leaf spot and soft rot in particular. A daily misting routine is close to what you would design if you were trying to encourage them.

There is one place misting earns its keep, and it is worth separating from the other: inside a closed propagation box or a cabinet, where you are wetting a small sealed volume rather than a room, and where the point is keeping an unrooted cutting from drying out. That is a different act from spraying a Monstera on an open shelf.

What does work, in rough order of how much difference it makes:

  • An enclosure. A cabinet, a converted greenhouse, a clear box over a cutting. It works because it is a closed volume, which is the only way to hold a humidity level far above the room's for any length of time.
  • A humidifier sized to the room, placed near the plants but not blowing onto them, with a hygrometer somewhere you will actually look at it. It comes with maintenance: a warm reservoir grows things, an ultrasonic unit will aerosolise whatever is growing along with the water, and hard water leaves a fine white mineral dust over everything nearby.
  • Grouping plants. Real, and modest — transpiration lifts the humidity in the shared air immediately around the leaves. It costs nothing, so it is worth doing.
  • Pebble trays have the same problem as misting. The evaporating surface is small and the effect is local and slight.

And the trade-off nobody mentions when selling you a cabinet: warmth, high humidity and still air together are the conditions under which fungal and bacterial problems flourish and under which a saturated mix never dries out. A cabinet without a fan is an incubator. Air movement is not a compromise you make against humidity — it is a requirement that arrives with it. It also strengthens petioles and keeps fungus gnat numbers down.

Finally, leaves acclimatise even though a plant cannot make an existing leaf over. A leaf that developed at 80 per cent and then meets a 45 per cent room will crisp at the edges; the same plant, growing its next leaf at 45 per cent, is usually fine. That is why a plant bought out of a grower's greenhouse often looks miserable for two months and then quietly gets on with it, and why opening a cabinet gradually beats opening it.

Temperature

Roughly 18 to 29 °C suits nearly everything here, which is the range the genus pages give. Growth slows noticeably below about 15 °C, and chilling injury — damage with no frost involved at all — begins for many tropical foliage plants somewhere below 10 to 12 °C.

The three routine ways a houseplant gets cold are all avoidable: leaves resting against window glass overnight in winter, a draught from a door or an air conditioner blowing straight at a plant, and the journey home from the shop in an unheated car. The last of those accounts for more losses than the weather does.

Cold damage shows first as patches that look water-soaked and greyish green, which turn dark brown or black over a day or two, usually on whatever part was nearest the cold. Sometimes the plant simply goes limp and does not come back. It is worth separating from the two things it is confused with. Sun scorch is dry, tan or bleached, sharply outlined, and on the side facing the sun. Bacterial soft rot is mushy, spreads visibly from one day to the next, often has a yellow halo and sometimes a smell. Cold damage does not spread once the cold event is over, and that is the useful test.

At the top of the range, above about 30 °C in dry air, a plant can wilt with a soaking wet root ball because it is losing water through the leaves faster than the roots can supply it. Shade and humidity fix that. More water does not, and will finish the job.

Substrate

Aroid mixes are chunky because of where these roots evolved. Most of these plants are hemiepiphytes: they root into leaf litter, moss and loose bark on the side of a tree, in a material that is drenched by rain and then drained and aerated within the hour. A pot of fine peat compost is the opposite of that — small pores, and a saturated zone at the bottom that never leaves.

The variable that actually matters is air-filled porosity: the fraction of the pot that is still air once it has finished draining. Container-media work generally aims somewhere in the region of ten to twenty per cent for nursery crops, and aroid mixes are deliberately built at the top of that or past it. That extra air is what buys the margin for error when you water.

What each component is actually for:

  • Orchid bark, pine or fir, medium grade, is the structure — it is what creates the large pores. It also decomposes, which is why a mix that worked beautifully for two years quietly stops working: as the particles break down the pore size falls and the air goes out of the pot. That is a common cause of a plant rotting for no apparent reason when nothing about the watering changed. Decomposing bark also ties up nitrogen, because the microbes doing the decomposing take it first, so a bark-heavy mix wants feeding.
  • Perlite is expanded volcanic glass — near enough inert, holds little water, adds pore space, weighs nothing. It floats up to the surface with repeated top watering, and dry perlite dust is a respiratory irritant, so wet the bag before you dig into it.
  • Pumice does the same job and is better in most respects: it does not float, it does not break down, it holds a little water in its own pores, and its weight keeps a tall plant from tipping over. It is heavier to carry and harder to find, which is more or less the entire argument for perlite.
  • Horticultural charcoal is another non-decomposing chunk that holds a little water. The claim that it purifies the mix or keeps it sweet is inherited from aquarium filtration and is not something I can support at the scale of a plant pot. Use it as structure and do not expect chemistry from it.
  • Coco coir is the water-holding fraction, and better behaved than peat, which turns hydrophobic when fully dry and then channels water down the sides of the root ball rather than wetting it. The catch is chemistry: unbuffered coir carries a great deal of potassium and sodium on its exchange sites and will trade them for your calcium and magnesium. Buy it buffered, or rinse it and feed with something that includes calcium and magnesium.
  • Sphagnum moss holds a lot of water while staying open, which makes it excellent for rooting cuttings and for wrapping an aerial root. It also compacts and degrades, and on the day it does it goes from ideal to airless without announcing itself. Worth knowing: sphagnum is the established source of sporotrichosis, the skin infection sometimes called rose gardener's disease. Gloves are not paranoia.
  • Worm castings or a little compost bring some nutrition and some biology. Keep the proportion small — they are fine-textured, and fine texture is the thing the rest of the mix exists to avoid.

Two starting points, where the reasoning matters more than the ratio. For a general climbing aroid — Monstera, most Philodendron — about two parts medium bark, one part perlite or pumice, one part coir and a handful of charcoal. The bark sets the pore structure, the coir stops the pot drying out in a day and a half, the perlite or pumice tops the air back up, and the whole thing wants remaking every year or two as the bark goes. For the plants that resent drying — Alocasia, the velvety Philodendron, Anthurium — shift that same mix toward water: less bark, more coir, and some chopped sphagnum. You are trading away margin for error in exchange for roots that will not forgive a full dry-out.

The mix and the way you water are one system, and that matters more than any recipe. A chunky mix in the hands of someone who waters once a fortnight regardless is worse for a plant than plain compost in the hands of someone who checks. Pot material is part of the same system: terracotta loses water through its wall, so the same mix in terracotta needs either a more retentive recipe or a shorter interval than it does in plastic.

Fertilizer

Dilute and regular beats strong and occasional, and the reason is osmotic. A root takes up water because the solution inside it is more concentrated than the solution outside it. Pour in a strong feed and you invert that gradient, so water leaves the root instead of entering it — that is what fertiliser burn is, before any specific ion toxicity gets involved. A weak solution given often keeps the salt concentration in a range roots can work against, and it is closer to the way nutrients actually arrive in the wild, which is continuously and in traces.

The three numbers on the bottle are percentages by weight of nitrogen, phosphorus and potassium, but only the first is what it appears to be. Phosphorus is conventionally expressed as P2O5 and potassium as K2O, both conventions inherited from the nineteenth century, so a 20-20-20 is not equal parts of three elements. What the ratio tells you in practice is that nitrogen drives leaves and stems, which is what you want from a foliage plant; phosphorus goes to roots and flowering, and foliage plants need far less of it than the bloom-booster shelf implies; and potassium regulates water relations and general function. Check as well that the bottle carries micronutrients, and whether it carries calcium and magnesium — many do not, and a coir-based mix particularly wants them.

In practice: a balanced complete feed at a quarter to a half of the label rate, with most waterings, while the plant is actively growing. Less, or nothing at all, when it is not. A plant in a dim winter room that has stopped growing cannot use what you give it, and the surplus is simply salt accumulating around its roots. Do not feed a plant that is sick, one that has just been repotted, or one whose roots are damaged, and never feed into dry substrate — wet it first.

Salt build-up is the slow failure mode of a well-meant feeding routine. It shows in the pot as a white or tan crust on the surface of the mix and around the rim, and on the plant as brown crisp tips and margins that look exactly like a humidity problem and are not. The fix is to flush: plain water, several times the pot's volume, all of it allowed to run out, every couple of months for anything fed regularly. That is also the argument for top watering periodically even if bottom watering is your habit.

Slow-release pellets are convenient and hard to dial back. They release faster when it is warm and wet, which is often exactly when a struggling plant is least able to use what they release, and once they are in the pot you cannot take them out again.

Repotting

The reasons to repot are: the roots have filled the pot, so it dries much faster than it used to and water runs straight through; roots are coming out of the drainage holes or pushing the plant up out of the pot; or — the one people forget, and the more common one for aroids — the mix has broken down. A bark mix two or three years old is no longer the mix you made. It has gone fine and dense, the air has left it, and the plant will start behaving as though it is being overwatered although nothing about your watering changed. That is a reason to repot into fresh mix even when the pot is still the right size.

Every spring is not a reason on its own, though repotting into the growing season does mean the plant re-establishes faster.

Go up about one pot size — a couple of centimetres of extra diameter. Skipping ahead to save yourself the job later is the single most common repotting mistake, and the mechanism is the same one as overwatering: a large volume of mix with a small root ball in the middle of it has no roots drawing water out of the outer part, so that part stays wet for weeks, and the root ball sits in the middle of a permanently damp mass. Roots also colonise an appropriately sized pot faster than an oversized one.

The method: water the plant the day before, so it is hydrated when you disturb it. Tease the outside of the root ball loose and unwind anything circling the bottom, or it will go on circling. Cut away whatever is brown, soft and hollow — healthy aroid roots are firm and pale, and rotted ones slide out of their own skin when you pull at them. Keep the plant at the depth it was at before. Water thoroughly to settle the mix around the roots, skip fertiliser for a few weeks, and keep it out of the harshest light for a week while it re-establishes.

Propagation

The node is the whole thing. A node is the point on the stem where a leaf attaches — a slight swelling with a ring or scar around it, usually carrying a dormant bud and often an aerial root or the nub where one would be. It is where new growth comes from. A leaf and its petiole with no piece of stem attached will sometimes root and will never become a plant; it sits there, green and going nowhere, until it gives up. That is the most common way a Monstera cutting is wasted. Some plants do grow from a leaf, Begonia and Sansevieria among them. Aroids do not.

Aerial roots help without being magic. They are roots that already exist, so a cutting that carries one establishes faster. Expect them to die back partly once they go into water or a pot — they were built for air, and the plant will grow new roots suited to whatever it is now in.

What to root it in, and what each is like to live with:

  • Water is the easiest to watch and the hardest to move on from. Roots grown submerged have a different structure and fewer functioning root hairs, and a cutting left until it has a large water-root system often sulks badly when potted. If you root in water, pot early — at two or three centimetres of root — and keep the mix wetter than usual for the first few weeks.
  • Sphagnum, wrung out so it is damp rather than sodden, holds high humidity right at the node and produces roots much closer to what the plant will want in a pot, so it transitions well. Its failure mode is being packed too wet or too tight, at which point it is a rot chamber.
  • Perlite, damp, in a closed container — often with a centimetre of water in the bottom and the cutting held above it — is airy and wet at the same time, which is exactly what root initiation wants. It works very well and gets less attention than it deserves.
  • Semi-hydro, meaning LECA or a mineral pon over a reservoir, produces roots adapted to constant moisture plus air, and it works. Treat it as a destination rather than a stage, because those roots transition into soil about as badly as water roots do. It is inert, so everything the plant eats has to arrive in a dilute nutrient solution.

What actually determines whether a cutting takes has little to do with which of those you choose:

  • A node. Nothing else on this list matters without one.
  • Warmth. Root initiation is temperature-driven, and the same 20 to 28 °C the plants like is where cuttings root. A cutting on a cold windowsill in February will sit for two months; the same cutting in July roots in a fortnight. Gentle bottom heat is the single most effective thing you can do.
  • Humidity around the leaf. The cutting has to keep a leaf alive with no roots to replace what that leaf loses. A clear bag or box over it takes the race away.
  • Light. Bright and indirect. It still has to photosynthesise, and it cannot survive direct sun with no root system.
  • A clean cut. A sharp, sterilised blade, cut just below the node rather than crushed through it. Letting the cut dry for an hour before it goes into a wet medium is common practice and a cheap way to reduce rot at the wound.
  • Patience. A good deal of it is not working is a cutting being lifted out and inspected every three days.

Rooting hormone is genuinely useful for woody cuttings and largely beside the point for aroids, which root readily without it.

Dormancy

Most of these plants have no true dormancy. They slow down over winter because there is less light and it is cooler, and they pick up again when that reverses. All that asks of you is that the watering and the feeding slow down with them rather than carrying on at the summer rate into a plant that has stopped using either.

Alocasia is the exception and worth knowing about, because it is genuinely dormant: in low light and cooler temperatures it drops its leaves and rests as a corm. The plant is not dead. Keep the mix barely damp, stop feeding, do not repot, and wait. Most Alocasia that are lost are lost by being treated as sick — watered more, fed, repotted — while they were merely asleep.

Pests

Two rules first, because they matter more than any individual treatment.

Quarantine every new plant, from every source including the good ones, for three to four weeks somewhere it cannot touch anything else, and look at the undersides of its leaves once a week. Three weeks covers an egg-to-adult cycle for most of what you are worried about. Nearly every collection-wide infestation walked in on one new plant.

Treat repeatedly, on a schedule. Almost nothing you can spray kills eggs. A single application kills the population you can see and hands the next generation an environment with no competition in it. Whatever you use, use it again in five to seven days, and again after that, and treat the neighbouring plants rather than only the one you found it on.

Thrips

Slender insects one or two millimetres long, dark and narrow as adults, pale yellow and quick as larvae, and easiest to find by tapping a leaf over a sheet of white paper. They puncture cells and drink the contents, so the damage is silvery or bronze stippling and streaking, often with tiny black varnish-like specks of frass beside it, and new leaves that open already distorted and scarred. They are the hardest of the five to be rid of, because part of the life cycle happens off the leaf — in the substrate, or in the crevices of the pot — where a spray never reaches. Washing the plant physically, treating over several weeks rather than several days, and predatory mites of the Amblyseius and Neoseiulus group are what actually clears a persistent case; blue sticky cards are how you find out whether you have won. Worth taking seriously rather than tolerating: thrips transmit tospoviruses, and nothing cures those.

Spider mites

Not insects but arachnids, under half a millimetre, living on the undersides, and normally noticed as damage rather than as animals: fine pale stippling that reads as dust until you look closely, and then a bronze or yellow cast across the whole leaf. Visible webbing means it has been going on for a while. They multiply explosively in warm dry air, which is what makes humidity and a periodic rinse a real control measure here rather than a nicety. Forceful water on the undersides, repeated; horticultural oil or insecticidal soap with genuinely complete coverage of the undersides, repeated every five to seven days; Phytoseiulus persimilis for a serious case. Avoid reaching for a broad-spectrum pyrethroid — mite populations recover from those faster than their predators do, and infestations regularly get worse after one.

Mealybugs

White, cottony, slow-moving, tucked into leaf axils, along petioles, into new growth and under the rim of the pot. The waxy coat is why contact sprays underperform on them, and why the reliable small-scale treatment is mechanical: a cotton bud dipped in 70 per cent isopropyl alcohol, one insect at a time, followed by insecticidal soap or oil across the whole plant, repeated. If a plant keeps reinfesting after you have cleared everything visible, take it out of the pot and look at the roots — root mealybugs are the same animal living where you are not looking. Ants running up and down a plant are usually farming something.

Fungus gnats

Small dark flies drifting around the pot. The adults do nothing but annoy you; the larvae live in the top few centimetres of wet substrate and eat fungi, organic matter and fine roots, which matters much more for seedlings and cuttings than for an established plant. They are a symptom before they are a pest, because what they need is a surface that is permanently damp. Let the top of the mix dry between waterings, switch to bottom watering, and put a physical layer over the surface. Yellow sticky traps take the adults; for the larvae the specific and effective treatment is Bacillus thuringiensis subsp. israelensis, sold as mosquito bits and steeped in the watering can.

Scale

Small brown or tan bumps along stems and leaf midribs that do not wipe off, because what you are looking at is a shield with an insect underneath it. Soft scale also produces honeydew, so a sticky leaf and then black sooty mould growing on the stickiness is often how they are found. Sprays reach the mobile crawler stage and barely touch an adult under its shield, which is why horticultural oil — which works physically, by smothering — outperforms most things here, and why removal by hand with a fingernail or an old toothbrush is worth the time it takes. Expect weeks. Scale is slow in both directions.

Whatever you reach for: identify the pest before you treat it, test any spray on one leaf and wait a day, cover the undersides because that is where nearly everything lives, and do not put oil on a plant standing in direct sun or already heat-stressed.

Common problems

Most people arrive at a page like this from a symptom, so here they are that way round. In almost every case the first two questions worth asking are what the light is like and what the roots look like, because between them they are the answer more often than everything else combined.

Yellowing leaves

The most common cause by a wide margin is too much water for too long: the roots are not getting air and the plant is shedding leaves it can no longer support. It shows on the oldest, lowest leaves first, with a soggy mix underneath. One old leaf yellowing slowly while the plant is otherwise growing well is ordinary senescence and not a problem; several at once is. Uniformly pale new growth points instead at nitrogen or at light. Yellow between veins that are still green, on new leaves, points at iron or manganese, which in a coir mix is usually a pH or a calcium-magnesium problem rather than an actual absence of the nutrient.

Brown crispy edges and tips

Three candidates, and they are distinguishable. Low humidity gives a thin brown margin, often with a yellow band inside it, on the leaves most exposed to moving dry air. Salt accumulation takes the tips first and comes with a crust on the surface of the mix or the rim of the pot — flush it. And letting the plant go too dry too often does the same thing; that is the one people rule out because they believe they water plenty. If the mix is dry several centimetres down more often than it is not, it is that.

Brown mushy spots

Water sitting on leaves plus still air, which means bacterial leaf spot or blight — the classic aroid pathogens, Xanthomonas and the soft-rot Pectobacterium, need liquid water on the surface to get in. It is mushy, it spreads day by day, it often has a yellow halo and sometimes a smell. Cut well past the margin with a clean blade, isolate the plant, stop wetting the leaves and get air moving; fungicides do very little to a bacterium. If the spots appeared after a cold night and are not spreading, it is cold damage instead. If they came up from the base and the pot is wet, the problem is at the roots and the leaf is only reporting it.

No fenestration

Light, in almost every case, and long before it is a question of age. A Monstera that was making fenestrated leaves and is now making entire ones has told you its light dropped. That said, juvenile leaves are entire in these plants regardless — a small young plant has not earned them yet — and a climber given something to climb produces larger and more fenestrated leaves than the same plant sprawling, because leaf size in these species responds to having height and support.

Leggy growth

Long stretches of bare stem between leaves, each new leaf smaller than the one before. This is a light problem, straightforwardly, and it will not fill back in — the stem that stretched is the stem you have. The fix is more light for whatever grows next, and cutting the leggy section off and rooting it if you want a fuller plant. Do not fertilise it in the hope of pushing growth: more nitrogen in poor light produces more weak growth.

Sudden collapse

Take it out of the pot. Root rot is the usual answer and it is unambiguous once you look — firm and pale is healthy, brown and soft and sliding out of its own skin is not. Also worth ruling out, in rough order: a cold event a few days earlier, a fertiliser burn, root damage from a recent repot, and a complete dry-out, since a plant that lost its fine roots to drought often looks fine until you water it and then goes over. And if it is an Alocasia in autumn, dig for the corm before you throw anything away. It is very often dormant rather than dead.

Where the species differ

All of the above is the baseline. Where a plant departs from it, its own page says so: each species page carries a care table built from its genus default, with every field the species wants differently marked as a departure and the genus value shown underneath for comparison. If the species page is silent on something, this page is what it means.