Velvet Calathea problem - Ask Extension
This plant was doing very well in a southwest window for 6 months. Watering approximately weekly (but using a water meter as a guide - Water @ WM#7) w...
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Velvet Calathea problem #809739
Asked September 06, 2022, 5:10 PM EDT
This plant was doing very well in a southwest window for 6 months. Watering approximately weekly (but using a water meter as a guide - Water @ WM#7) with a weekly 10/15/10 fertilizer for spring & summer. I also mist it daily. It is in a well drained pot inside a larger pot and sits in a humidity tray that I check daily.
But in the last 2 weeks, it has gone downhill. I switched it to a Northeast window thinking it may have been getting too much sun but there is no change. Then I re-potted it and checked the roots, concerned that it may have been over-watered, but the roots looked healthy and it is certainly not root bound. I looked online for clues but the only thing I could find is that it doesn't like fluoridated water - so I will switch to distilled water beginning with the next watering. Could that be the only problem, or is could it be something else?
I'm attaching an image so you can see what is happening. The leaves are becoming discolored and yellow around the edges as well as staying in a drooping down position. The leaves do not fold up at night any longer.
Baltimore City County Maryland
Expert Response
Calatheas can be fickle plants, needing more exacting conditions to thrive than some other tropical houseplants. Generally, they want moderate indirect light (limited direct sun or lots of indirect light), high humidity, and typical home temperatures (so, no cool drafts in winter or too close to an A/C vent in summer). It's hard to tell exactly what is stressing the plant from the photos, but it's likely environmental conditions as opposed to pests or disease, at least as the primary factor. (A secondary pest issue is always possible.)
Our prime suspect with the decline of most houseplants is root stress, often from too much or too little water. It's possible this plant's roots are beginning to suffer from root rot while not yet looking infected, but it's hard to say. Sometimes over-watering takes a surprising amount of time to manifest as plant decline. Make sure the pot drains well and any cache pot (outer pot with no holes) or saucer that it sits on does not collect water for long; empty it promptly after watering or the moisture could seep back into the drain holes and over-saturate the roots, depriving them of needed oxygen.
Humidity trays run the risk of over-saturating the soil if the pot isn't kept raised above the water in the tray, but even when that's addressed, they don't tend to raise ambient humidity around the plant very much (room humidifiers tend to be better for this), so probably aren't worth the trouble of keeping the water level just right and the pebbles or other supports clean of algae, mold, or bacteria.
Avoid misting the leaves, aside from the occasional shower to remove dust. Wet leaf surfaces are more vulnerable to infection, and even though we don't see signs of that here, it could occur in the future. Plus, this does even less for a humidity boost than a humidity tray, so serves little purpose while adding to the risk of future problems.
Yes, Calathea are known to be sensitive to fluoride in tap water, and possibly also to mineral buildup in the potting mix from both tap water minerals and salts. (Salts in this context don't necessarily mean sodium; instead, they refer to any mineral residues that are left behind that the plant doesn't use and which don't leach out of the soil with future waterings.) Regular repotting every year or so (more or less) can reset the salt levels by exchanging the current soil for fresh, but you can also try fertilizing less and using a purer water source. Distilled water might work but it should be fine to use tap water to dissolve your fertilizer in. (Using distilled for mixing a fertilizer that isn't specifically designed for use with distilled water could interfere with its acidity and nutrient ratios.)
You might be fertilizing too often; weekly sounds a bit high but it would depend on the dosage/dilution you're using. If much weaker than the rate recommended on the product label, than it may be fine to use in spring and summer if you discontinue use in autumn and winter. Otherwise, try backing-off the application of fertilizer to a monthly interval.
When watering, feel the soil about an inch down and only water once it's becoming somewhat dry to the touch at that depth.
We might be seeing a bit of fine stippling damage on the leaves from spider mites, but we can't enlarge the image enough to be sure. Check for paler speckles on the leaves like those in the sample photos on the linked page, because the mites themselves are very tiny and might not be producing any obvious webbing from which they get their name. Spider mites are common indoor plant pests because they thrive in the lower humidity and overall drier conditions (no rain to keep washing them off the leaves). If necessary, they are treatable with low-toxicity pesticides, but read the product labels carefully when choosing one to make sure that not only is it labeled for indoor use, but that Calathea tolerate exposure -- some plants are pesticide-sensitive, even when they're applied as directed and may develop tissue damage from contact with the chemical.
Miri
Our prime suspect with the decline of most houseplants is root stress, often from too much or too little water. It's possible this plant's roots are beginning to suffer from root rot while not yet looking infected, but it's hard to say. Sometimes over-watering takes a surprising amount of time to manifest as plant decline. Make sure the pot drains well and any cache pot (outer pot with no holes) or saucer that it sits on does not collect water for long; empty it promptly after watering or the moisture could seep back into the drain holes and over-saturate the roots, depriving them of needed oxygen.
Humidity trays run the risk of over-saturating the soil if the pot isn't kept raised above the water in the tray, but even when that's addressed, they don't tend to raise ambient humidity around the plant very much (room humidifiers tend to be better for this), so probably aren't worth the trouble of keeping the water level just right and the pebbles or other supports clean of algae, mold, or bacteria.
Avoid misting the leaves, aside from the occasional shower to remove dust. Wet leaf surfaces are more vulnerable to infection, and even though we don't see signs of that here, it could occur in the future. Plus, this does even less for a humidity boost than a humidity tray, so serves little purpose while adding to the risk of future problems.
Yes, Calathea are known to be sensitive to fluoride in tap water, and possibly also to mineral buildup in the potting mix from both tap water minerals and salts. (Salts in this context don't necessarily mean sodium; instead, they refer to any mineral residues that are left behind that the plant doesn't use and which don't leach out of the soil with future waterings.) Regular repotting every year or so (more or less) can reset the salt levels by exchanging the current soil for fresh, but you can also try fertilizing less and using a purer water source. Distilled water might work but it should be fine to use tap water to dissolve your fertilizer in. (Using distilled for mixing a fertilizer that isn't specifically designed for use with distilled water could interfere with its acidity and nutrient ratios.)
You might be fertilizing too often; weekly sounds a bit high but it would depend on the dosage/dilution you're using. If much weaker than the rate recommended on the product label, than it may be fine to use in spring and summer if you discontinue use in autumn and winter. Otherwise, try backing-off the application of fertilizer to a monthly interval.
When watering, feel the soil about an inch down and only water once it's becoming somewhat dry to the touch at that depth.
We might be seeing a bit of fine stippling damage on the leaves from spider mites, but we can't enlarge the image enough to be sure. Check for paler speckles on the leaves like those in the sample photos on the linked page, because the mites themselves are very tiny and might not be producing any obvious webbing from which they get their name. Spider mites are common indoor plant pests because they thrive in the lower humidity and overall drier conditions (no rain to keep washing them off the leaves). If necessary, they are treatable with low-toxicity pesticides, but read the product labels carefully when choosing one to make sure that not only is it labeled for indoor use, but that Calathea tolerate exposure -- some plants are pesticide-sensitive, even when they're applied as directed and may develop tissue damage from contact with the chemical.
Miri
