Plant care

Light

Lighting can be tough to get right. “Bright indirect” is the most repeated and least useful phrase in the hobby. What it actually means is this: as much light as you can give the plant without the sun’s disc hitting the leaves for any length of time (i.e. no direct line of sight).

Generally for indoor plants we measure light in foot-candles; a lux meter measures the same thing in different units, and one foot-candle is about 10.8 lux. The extension services do not agree on where the brackets fall — one puts “low” at 25 to 100 foot-candles and another at 50 to 500¹² — so treat these as rough: low light around 50 to 250 foot-candles, 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 around 100,000 lux, and a well-lit office is a few hundred. That gap tells us something important. Our eyes adapts logarithmically, which makes them a terrible light meter. A room that feels bright to us can easily be sitting at the bottom of the low light bracket.

Phone light-meter apps read the ambient-light sensor next to the front camera. It’s uncalibrated, its angular response is poor, and two phones side by side will disagree by a lot. So use an app for comparison — this shelf against that shelf, same phone, same minute; or the same shelf in June and again in December — and don’t trust the absolute number. If you want the absolute number, a cheap dedicated lux meter is the way to go.

Distance from the window is a worse rule of thumb than it looks. What predicts the light a leaf gets is how much open sky it can see. A plant a metre back from a big unobstructed window with a clear view upward does better than one pressed against a small window facing a wall. And light drops off quickly as you move inward — a spot that looks only slightly dimmer usually measures as a fraction of the total light. In the northern hemisphere, an unobstructed south window is the strongest. East gives gentle direct morning sun that most aroids are fine with, west gives harsh afternoon sun, and north gives even but weak light.

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

Getting too much. Pale washed-out patches that go dry, tan or bone-white, 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. Substrate drying very fast.

Getting too little. Gaps between the leaves stretching out, each new leaf smaller than the last, fenestration reduced or gone, the whole plant leaning toward the window. And the one that gets misdiagnosed constantly: the pot staying wet far longer than it used to. People treat that as overwatering. It isn’t — the plant simply isn’t drinking, because it isn’t working.

A leaf is built for the light it grew in, and it can’t rebuild itself. Move a plant out of a dim corner into a bright window and you’ll scorch the leaves it already has, even though the new spot is the right one. Move it in stages over a week or two, and let the new growth arrive already acclimatised.

Water

The rule for when to water is about the substrate drying out, 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 there, what the mix is made of — changes through the year, and differs between two rooms in the same flat. A fixed interval can only ever be right for part of that.

Which is why “water weekly” kills plants. The interval that’s roughly right 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 isn’t caused by water. It’s 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 molds that are always there anyway, Pythium and Phytophthora and their relatives, move into tissue that’s already dying. That’s the whole reason a chunky mix is forgiving: it refills with air fast.

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

• Weight. Lift the pot right after a thorough watering, then lift it again a few days later. That difference is more reliable than anything else you have access to, 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 answer 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 goes bone dry. Alocasia want to stay damper than that, and they’ll charge you for a full dry-out in dropped leaves. Consider a semi-hydro or self-watering setup for Alocasias to keep them constantly damp and reduce maintenance.

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 further down, never reaches half the roots, and concentrates fertiliser salts in the pot instead of carrying them out.

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’s turned hydrophobic and now channels water straight down the sides of the root ball, and a fungus gnat problem, since the surface stays dry. The cost is the exact mirror of top watering’s benefit — it never flushes anything out, so salts travel upward with the evaporating water and pile up at the surface. 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 do what people think it does. Water won’t cross from a fine layer into a coarse one until the fine layer is saturated — so the gravel lifts the saturated zone up into the root ball rather than draining it away.³ One bench test found layers modestly helpful in chunky mixes and harmless otherwise, so the honest summary is that they’re not the fix;⁴ coarser mix throughout and a drainage hole are.

Water quality matters less than the hobby suggests, for most people and most aroids. It starts to matter when your water is very hard or high in dissolved solids, because the deposits build up in the mix and drift its pH, and that shows up fastest in sphagnum or semi-hydro where there’s little to buffer it. It matters if you grow something documented as fluoride-sensitive — that list is longer than it looks — Dracaena, Chlorophytum, Cordyline, the prayer-plant family, and among aroids Spathiphyllum and Aglaonema, where it produces tip necrosis — and fluoride also arrives in perlite and superphosphate, with a low pH making uptake worse.⁵⁶ Monstera and Philodendron aren’t on it. And it matters absolutely if your supply runs through an ion-exchange water softener, which trades calcium for sodium and gives you 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. But many utilities — more than one in five Americans’ supplies, and a growing number elsewhere — disinfect with chloramine instead,⁷ which was picked precisely because it’s more stable and doesn’t meaningfully off-gas in a jug on the counter. So if you have chloraminated water and a reason to remove it, standing it overnight is not the method. Rain or reverse-osmosis water is worth the trouble when your tap water is hard, and mostly isn’t 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’s worth being careful about what’s actually known.

The received wisdom says aroids need 70 to 80 percent humidity and a daily misting. What holds up is narrower than that. The common climbing aroids — Monstera, most Philodendron — grow perfectly well at ordinary indoor humidity, somewhere in the 40 to 60 percent range. Higher humidity does give you visibly better plants: bigger leaves, new leaves that unfurl cleanly instead of sticking and tearing, less crisping at the margins. Growers aren’t imagining that. But grows better above 60 percent is a different claim from needs 70 percent, and it’s 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 — plus Alocasia, which in dry air picks up spider mites as a matter of course rather than as bad luck.

Temperature is missing from all of this. What a leaf actually experiences isn’t relative humidity — it’s the gap between the water vapour the air is holding and the amount it could hold. Growers call that vapour pressure deficit, and it depends on temperature as much as on the humidity reading. Fifty-five percent at 64 °F (18 °C) is a far gentler place to be than fifty-five percent at 82 °F (28 °C). That’s why the same plant behaves differently in a cool bedroom and a warm living room at an identical hygrometer reading.

Misting does very little A few millilitres of water evaporating into a room’s worth of air moves the room’s relative humidity by an amount we couldn’t measure, and the local effect at the leaf surface is gone within minutes. Set against that: how long a leaf stays wet is the standard predictor of infection in plant pathology. Bacterial and fungal leaf pathogens need liquid water sitting on the surface for hours 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’d design if you were trying to encourage them.

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

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

• An enclosure. A cabinet, a converted greenhouse, a clear box over a cutting. It works because it’s a closed volume, and that’s the only way to hold a humidity level far above the room’s for any length of time.
• A humidifier sized to the room, near the plants but not blowing onto them, with a hygrometer somewhere you’ll 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 right around the leaves. It costs nothing, so you may as well.
• Pebble trays have the same problem misting does: the evaporating surface is small and the effect is local. Extension services still recommend them,⁸ and nobody has measured the difference either way, so take this as common sense rather than as a finding — it is reasoning we are doing here, not a result anyone has.

And here’s the trade-off nobody mentions when it comes to a plant cabinet or enclosure: warmth, high humidity and still air together are exactly the conditions where fungal and bacterial problems flourish and a saturated mix never dries out. A cabinet without a fan is an incubator. Air movement isn’t a compromise you make against humidity — it’s a requirement that arrives with it. It also strengthens petioles and keeps fungus gnat numbers down.

Finally: leaves acclimatise, even though a plant can’t remake a leaf it already has. A leaf that developed at 80 percent and then meets a 45 percent room will crisp at the edges. The same plant, growing its next leaf at 45 percent, is usually fine. That’s why a plant bought out of a grower’s greenhouse often looks miserable for two months and then will continue growing fine.

Temperature

Roughly 64 to 84 °F (18 to 29 °C) suits most plants. Growth slows noticeably below about 59 °F (15 °C), and chilling injury — damage with no frost involved at all — starts for many tropical foliage plants somewhere below 50 to 54 °F (10 to 12 °C).

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

Cold damage shows up first as patches that look water-soaked and greyish green, turning dark brown or black over a day or two, usually on whatever part was nearest the cold. Sometimes the plant just goes limp and doesn’t come back. It’s worth telling apart from the two things it gets 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 doesn’t spread once the cold event is over — that’s the useful test.

At the top of the range, above about 86 °F (30 °C) in dry air, a plant can wilt with a soaking wet root ball, because it’s losing water through the leaves faster than the roots can supply it. Shade and humidity fix that. More water won’t, 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 gets drenched by rain and then drains and airs out 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 goes anywhere.

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

Here’s what each component is actually for:

• Orchid bark, pine or fir, medium grade, is the structure — it’s 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’s a common cause of a plant rotting for no apparent reason when nothing about your watering changed. Decomposing bark also ties up nitrogen, because the microbes doing the decomposing get 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 at nearly all of it: it doesn’t float, doesn’t break down, holds a little water in its own pores, and its weight keeps a tall plant from tipping over. It’s 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 it isn’t something we can support at the scale of a plant pot. Use it as structure, and don’t expect chemistry from it.
• Coco coir is the water-holding fraction, and it’s better behaved than peat — peat turns hydrophobic when fully dry and then channels water down the sides of the root ball instead of wetting it. The catch with coir is chemistry: unbuffered, it carries a great deal of potassium and sodium on its exchange sites and will happily 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 aren’t paranoia.
• Worm castings or a little compost bring some nutrition and some biology. Keep the proportion small — they’re fine-textured, and fine texture is the thing the rest of the mix exists to avoid.

Two starting points — and the reasoning matters more than the ratio. For a general climbing aroid, Monstera or 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, some chopped sphagnum. You’re trading away margin for error in exchange for roots that won’t forgive a full dry-out.

Keep in mind that the mix and the way you water matters more than any recipe does. 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 also an important factor: terracotta loses water through its wall, so the same mix in terracotta wants either a more retentive recipe or a shorter interval than it does in plastic.

Semi-hydro

Semi-hydro is growing in an inert medium — usually LECA, sometimes a mineral pon — with a reservoir of dilute nutrient solution in the bottom of the pot and the root ball sitting above it. Capillary action lifts the solution into the medium, so the roots get water and air at the same time, continuously, which is the thing an ordinary pot spends all its effort trying to approximate.

It is not a shortcut and it is not better. It is a different set of trade-offs.

What it buys us: no organic matter, so nothing decomposes and the pore structure never collapses — no repotting into fresh mix every second year. No fungus gnats, because there is no damp organic surface for larvae to live in. A reservoir that makes underwatering nearly impossible and overwatering structurally impossible. And roots you can see, which makes root rot something noticed early rather than discovered at the point of collapse.

What it costs: everything the plant eats has to arrive in the water, because LECA is inert and holds no nutrients of its own. A hydroponic feed at every top-up, at a fraction of label strength, all year — a plant in semi-hydro fed on plain water starves on a schedule. Salts accumulate in the medium as the solution evaporates, so the whole pot wants flushing under a tap every month or two. And the transition is the hard part, not the maintenance.

On the transition. Roots grown in soil and roots grown in constant moisture are built differently, and a plant moved across has to grow a second set. Expect it to sulk, and expect to lose some of the original roots — that is the process rather than a failure. It goes best in spring or summer on a plant that is growing well, and worst on a plant that was already struggling, which is precisely when people reach for it as a rescue. A cutting rooted directly in LECA skips the problem entirely, because those roots were built for it from the start, and that is the easiest way in.

On the water line. Keep the reservoir below the bottom of the root ball, not around it. The medium wicks upward; roots sitting permanently submerged are back to the airless pot this was all supposed to avoid. A tall pot or a clear cache pot makes that easy to judge.

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 flip that gradient, so water leaves the root instead of entering it. That’s what fertiliser burn is, before any specific ion toxicity even gets involved. A weak solution given often keeps the salt concentration in a range roots can work against, and it’s much closer to how nutrients actually arrive in the wild: 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 early analytical chemistry, so a 20-20-20 is not equal parts of three elements. What the ratio tells us in practice: nitrogen drives leaves and stems, which is what you want from a foliage plant. The “phosphorus for roots and flowers” rule on the shelf is an oversimplification, and foliage plants need far less of it than the bloom-booster aisle implies;⁹ and potassium regulates water relations and general function. Check as well that the bottle carries micronutrients, and whether it carries calcium and magnesium — plenty don’t, 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 isn’t. A plant in a dim winter room that has stopped growing can’t use what you give it, and the surplus is just salt piling up around its roots. Don’t feed a plant that’s sick, one that’s just been repotted, or one with damaged roots — and never feed into dry substrate. Wet it first.

Salt build-up is the slow failure mode of a well-meant feeding routine. In the pot it shows as a white or tan crust on the surface of the mix and around the rim. On the plant it shows as brown crisp tips and margins that look exactly like a humidity problem and aren’t. 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 you feed regularly. That’s 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’s warm and wet, which is often exactly when a struggling plant is least able to use what’s released — and once they’re in the pot, you can’t take them out again.

Repotting

There are three reasons to repot. 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’s gone fine and dense, the air has left it, and the plant starts behaving as though it’s being overwatered even though nothing about your watering changed. That’s a reason to repot into fresh mix even when the pot is still the right size.

“It’s 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 as overwatering: a big volume of mix with a small root ball in the middle 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 a correctly sized pot faster than an oversized one.

The method: water the plant the day before, so it’s hydrated when you disturb it. Tease the outside of the root ball loose and unwind anything circling the bottom, or it’ll 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.

When the plant is new

A plant that has just arrived gets two things the others don’t, and both are about what came with it rather than about the plant.

Replace the top layer of the mix. Scrape off the top two or three centimetres and throw it away, then top up with your own. That layer is where fungus gnat eggs and larvae live, where a good deal of what a nursery sprayed has settled, and where scale crawlers and mealybugs sit when they move off the plant. It costs a minute and it removes most of what a new pot is likely to be carrying, without disturbing the roots at all. The rest of the mix can wait until the plant has settled in — a full repot and a house move in the same week is a lot to ask.

Wipe every leaf, both sides, with a cloth and dilute neem. Not a spray: a rag, one leaf at a time, with the underside done properly, because the underside is where nearly everything lives. It does two jobs at once — it physically removes eggs, scale and the early mealybugs that a spray would skate over, and it puts you nose-to-leaf with a new plant for five minutes, which is the single best way to find a problem while it is still one leaf’s worth of problem. Use a proper emulsified neem product rather than raw oil in water, which separates; keep the plant out of direct sun until it has dried, and do the leaf axils and the petioles while you are there.

Neither of these replaces quarantine — see Pests for that, and for why three weeks is the number. They just mean the plant starts its quarantine with far less on it.

Propagation

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’s 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 just sits there, green and going nowhere, until it gives up. That’s the most common way a Monstera cutting gets wasted. Some plants do grow from a leaf — Begonia and Sansevieria among them. Aroids don’t.

Aerial roots help, without being magic. They’re roots that already exist, so a cutting carrying 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 wherever it is now.

What to root it in, and what each one 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 working root hairs, so a cutting left until it has a big water-root system often sulks badly once 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’s 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’s 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 move into soil about as badly as water roots do. It’s inert, so everything the plant eats has to arrive in a dilute nutrient solution.

What actually decides whether a cutting takes has very little to do with which of those you pick:

• A node. Nothing else on this list matters without one.
• Warmth. Root initiation is temperature-driven, and the same 68 to 82 °F (20 to 28 °C) the plants like is where cuttings root. A cutting on a cold windowsill in February will sit there 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 is losing. A clear bag or box over it takes the race out of it.
• Light. Bright and indirect. It still has to photosynthesise, and it can’t survive direct sun with no root system.
• A clean cut. A sharp, sterilised blade, cutting just below the node rather than crushing 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 isn’t working” turns out to be a cutting that gets lifted out and inspected every three days.

Alocasia corms

Everything above is about a stem with a node on it, which is the right answer for a climbing aroid and the wrong one for an Alocasia. Alocasia mostly do not climb and mostly do not offer you a length of stem to cut. They multiply underneath instead.

Dig one out at repotting and you’ll find small firm nuggets along the rhizome, brown and about the size of a pea or a hazelnut. The hobby calls them corms; botanically they are closer to little tubers on a rhizome, and either way each one is a whole plant waiting to start. A mature plant makes several a year without being asked.

Separating them is easy. Take the plant out, wash enough mix off the roots to see what is there, and pull the corms away with your fingers — a ripe one detaches with almost no pressure, and one that resists is not ready, so leave it attached. Keep the papery brown skin on.

Rooting them is mostly a matter of not interfering:

• Damp sphagnum in a closed container, or a tray with a lid, or a bag. The point is humidity, which they want at close to saturation.
• Pointed end up. One end is slightly pointed and that is where the shoot comes from. Planted upside down a corm will usually still manage it, just later.
• Warmth, the same 68 to 82 °F (20 to 28 °C) that roots a cutting. Below that they simply wait.
• Light, once there is a leaf. Before that it makes no difference — the corm is running on its own reserves.
• Patience, and rather more of it than a cutting asks for. Two to eight weeks to a root, and often a while again before the first leaf. A corm that has done nothing for a month has not failed; a corm that has gone soft or hollow has.

Pot it up once it has a root and a leaf, into the same mix the parent is in, and keep it damper than an adult plant for the first month. One point worth knowing, because it catches people out: a corm potted straight into ordinary mix, at ordinary room humidity, very often does nothing at all and then rots. The closed container is not fussiness — it is the whole method.

And the timing is the same fact as the dormancy section. A plant that has dropped its leaves and gone quiet is a plant with a full set of corms on it, which makes the moment you think you have lost it the best moment to look.

Rooting hormone isn’t necessary for aroids — philodendron cuttings root at over ninety percent without it — but it does speed things up and produce bigger root systems, and the University of Minnesota recommends it on Monstera nodes.¹⁰¹¹ Optional, not pointless.

Dormancy

Most of these plants have no true dormancy. They slow down over winter because there’s less light and it’s 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.

Two of these are exceptions, and both are worth knowing about. Alocasia can go properly dormant. In low light and cooler temperatures it drops its leaves and rests on its thick underground stem — a rhizome, though the hobby calls the offsets corms.¹² A plant kept warm and bright may never do it, and one that does is not dead. Keep the mix barely damp, stop feeding, don’t repot, and wait. Most Alocasia that get lost are lost by being treated as sick — watered more, fed, repotted — while they were only asleep.

The Indian kale does it on a schedule rather than in response to conditions. It is deciduous: the foliage dies back in autumn whatever you do, the plant sits the winter out on its tuber, and it starts again in spring.¹³ Suspend watering as the leaves go, take off the withered growth, and either leave the tuber in its pot somewhere frost-free or lift it and store it dry. Start it back into growth at around 68 °F (20 °C).¹³ Cut pieces of tuber take about five more weeks than whole ones before anything shows, so a division doing nothing for a month is on schedule, not dead.¹⁴

Pests

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

Quarantine every new plant — from every source, including the good ones — for three to four weeks somewhere it can’t touch anything else, and look at the undersides of its leaves once a week. Three weeks covers a generation of thrips, spider mites and fungus gnats;¹⁵¹⁶¹⁷ mealybugs take six to eight weeks and scale longer still,¹⁸¹⁹ so keep looking after the quarantine ends. Nearly every collection-wide infestation walked in on a single new plant.

Treat repeatedly, on a schedule. Soaps and most sprays do not kill eggs; horticultural oil does, but only the eggs it actually coats.²⁰ 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 too, not just the one you found it on.

Thrips

Slender insects one or two millimetres long, yellow-brown to black and narrow as adults depending on the species, pale and quick as larvae,¹⁵ 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 next to it, and new leaves that open already distorted and scarred. They’re the hardest of the five to get 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. What actually clears a persistent case is washing the plant physically, treating over several weeks rather than several days, and predatory mites of the Amblyseius and Neoseiulus group; blue sticky cards are how you find out whether you’ve 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 usually noticed as damage rather than as animals: fine pale stippling that reads as dust until you look closely, then a bronze or yellow cast across the whole leaf. Visible webbing means it’s been going on 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. Don’t reach for a broad-spectrum pyrethroid — mite populations recover from those faster than their predators do, and infestations regularly get worse after one. Physically wiping off spider mites from all the leaves will make a huge difference.

Mealybugs

White, cottony, slow-moving, tucked into leaf axils, along petioles, into new growth and under the rim of the pot. That waxy coat is why contact sprays underperform on them, and why the reliable small-scale treatment is mechanical: a cotton bud dipped in 70 percent isopropyl alcohol, one insect at a time, then insecticidal soap or oil across the whole plant, repeated. If a plant keeps reinfesting after you’ve cleared everything visible, take it out of the pot and look at the roots — root mealybugs are a different animal, eyeless species of Rhizoecus built for life underground, but they reinfest the same way.²¹ 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’re a symptom before they’re a pest, because what they need is a permanently damp surface. 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. Consistent application of mosquito bits is key. Apply to all plants for at least a month during all waterings.

Scale

Small brown or tan bumps along stems and leaf midribs that don’t wipe off, because what you’re 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’re 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. 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’s where nearly everything lives, and don’t 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 — between them, they’re 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 aren’t 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, not a problem — several at once is. Nitrogen is mobile, so a shortage shows on the older leaves first, with small new growth. Pale, small new growth above normal old leaves points at light, or at an immobile nutrient, instead.²² 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 calcium-magnesium problem rather than an actual absence of the nutrient.

Brown crispy edges and tips

Three candidates, and you can tell them apart. 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 last one is the one people rule out, because they’re sure they water plenty. If the mix is dry several centimetres down more often than it isn’t, that’s what it is.

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’s 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. Ordinary fungicides do nothing to a bacterium, and copper sprays slow it without curing it.²³ If the spots appeared after a cold night and aren’t spreading, it’s cold damage instead. And if they came up from the base and the pot is wet, the problem is at the roots — the leaf is only reporting it.

No fenestration

Light, in almost every case, and long before it’s a question of age. A Monstera that was making fenestrated leaves and is now making entire ones has just told you its light dropped. That said, juvenile leaves are entire in these plants regardless — a small young plant hasn’t 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 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, and it won’t fill back in — the stem that stretched is the stem you have. The fix is more light for whatever grows next, plus cutting the leggy section off and rooting it if you want a fuller plant. Don’t fertilise it hoping to push growth: more nitrogen in poor light just gives you more weak growth.

Sudden collapse

Take it out of the pot. Root rot is the usual answer, and it’s 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’s an Alocasia in autumn, dig for the corm before you throw anything away. It’s 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 a species page is silent on something, this page is what it means.