Gadenin日本語Get the appDamp all the way through, never wet, never dry
A calathea has fine, shallow roots that sit in the top few inches of the pot. They die back within a day of the compost drying out completely, and they suffocate within a few days of sitting in water. The target is a compost that feels like a wrung out cloth at all times, which is a narrower band than most houseplants ask for.
This is why a calathea punishes a fortnightly routine. Water it the moment the top inch (2.5 cm) has dried and the layer below is still cool and damp. In practice that is every four to six days in a warm room and every ten to fourteen days in a cool one.
| What you find in the pot | What it means | What to do now |
|---|---|---|
| Top inch dry, deeper layer cool and damp | Exactly right | Water until it runs from the bottom |
| Dry two inches down | Slightly late | Water now and shorten the interval by two days |
| Dry through to the bottom, pot light | Root damage has started | Water, then expect a crisp edge on older leaves |
| Wet at the surface days after watering | It is not drying, and roots are at risk | Move it warmer and brighter, check the drainage |
A calathea that curls its leaves tightly in the evening is normal. A calathea that stays curled at midday with damp compost is telling you the roots cannot take water up, which is a root problem, not a thirst problem.
Water quality is the usual cause of crispy edges
The single most common complaint about this plant is a thin brown crisp line running around the edge of otherwise healthy leaves. In hard water areas that is almost always the water rather than the humidity. Calathea leaves are unusually sensitive to fluoride, chlorine and dissolved salts, and the damage collects at the leaf margin where the plant sheds water.
The tell is that the browning is even, edges only, and appears on old and new leaves alike over months. Damage from dry air is patchier and hits the tips first. Damage from underwatering comes with a limp, thin leaf, not a firm one.
| Water source | Suitability | Notes |
|---|---|---|
| Rainwater | Best | Free of fluoride and low in salts. Collect it and let it come to room temperature |
| Distilled or reverse osmosis | Very good | Reliable but you must feed, because it carries nothing |
| Filtered tap water | Fair | A carbon filter removes chlorine but not fluoride |
| Tap water left standing overnight | Fair | Chlorine gases off, fluoride and salts do not |
| Hard tap water straight from the tap | Poor | The usual reason edges brown in an otherwise well grown plant |
| Softened water | Avoid | An ion exchange softener adds sodium, which is worse than the hardness |
Flush the pot to clear built up salts
Fertilizer residue and minerals from tap water accumulate in the compost and concentrate as it dries. Once a season, take the plant to a sink and flush it, which resets the pot without repotting.
- Water slowly, four times over Pour tepid water through the compost until it runs freely, wait a minute, and repeat four times. You are washing salts out of the whole rootball rather than wetting it.
- Let it drain completely Leave the pot in the sink for twenty minutes. The compost should be damp, not sodden, before it goes back on its saucer.
- Scrape off any white crust A pale crust on the surface or around the rim is deposited salt. Remove the top half inch (1 cm) of compost and top up with fresh.
- Do not feed for a fortnight afterwards You have just stripped the pot of nutrients along with the salts. Wait two weeks, then resume feeding at half the strength on the bottle.
Adjust with the season, not the calendar
Water use follows room temperature and light almost exactly. The intervals below are for a plant in a six to eight inch (15 to 20 cm) pot indoors, and they are a starting point to adjust from what the compost is doing.
| Season | Room temperature | Interval | Point to watch |
|---|---|---|---|
| Spring | 64 to 75F (18 to 24C) | Every five to seven days | Growth restarts, so use goes up quickly |
| Summer | Above 75F (24C) | Every three to five days | Never let it dry out completely |
| Autumn | 61 to 72F (16 to 22C) | Every seven to ten days | Stretch the interval gradually, not in one step |
| Winter | Below 61F (16C) | Every ten to fourteen days | Water in the morning with tepid water |
Cold water on a calathea in winter checks the roots and the next leaf comes out small and marked. Let the water stand in the room overnight, or mix in enough warm water that it feels neither cold nor warm on your wrist.
Humidity is real, but it is the second problem
Calatheas do want humid air, and in a heated room in winter the air is often drier than a desert. But raising humidity will not fix edges that are browning because of the water, and people spend months misting a problem they are pouring into the pot.
Fix the water first, then raise the humidity, and judge the result on new leaves only. Damage already on a leaf never heals, so the only honest measure of any change is whether the next two leaves open clean.
- Group plants together Several plants standing close together raise the humidity between them measurably, and it costs nothing. It is more effective than misting once a day.
- Use a pebble tray properly A wide tray of gravel with water below the top of the stones, with the pot standing on the stones and not in the water. A narrow saucer of water does nothing.
- Run a humidifier in winter The only method that reliably holds 50 to 60 percent in a heated room. Place it a few feet away so the plant is in humid air rather than in a wet draft.
- Keep it out of moving air A heating vent, an air conditioner or a door that opens onto the cold dries the leaf edges faster than any humidifier can compensate for. Moving the plant is often the whole fix.
What to write down
The reason calathea watering feels like guesswork is that nobody remembers what they did six weeks ago. A few lines per watering turns it into something you can actually reason about.
Note the date, what you watered with, and the gap in days since the last time. Add a line whenever a new leaf unfurls and whether it opened clean or marked. After one season you can look back and see, for example, that every marked leaf followed a stretch when you fell back on tap water, or that your winter interval was consistently four days too short.
Photograph one particular leaf every few weeks from the same angle. Browning creeps so slowly that you cannot see it day to day, and a photograph from a month ago settles the argument.