What is causing these brown spots on calathea?
Kept indoors on a table in front of a window leading to a balcony ... No direct sunlight. Watering every 7-10 days when surface is dry to the touch but soil is not completely dry. Using tap water occasionally when rain water is unavailable. Very high humidity region ... currently 86%.
Comments (10)
ken_adrian Adrian MI cold Z5
last yearMaria Elena (Caribbean - USDA Zone 13a) thanked ken_adrian Adrian MI cold Z5Related Discussions
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Comments (2)Did you use a medium specifically formulated for potted plants - a potting medium? Inexpensive water meters are rather useless as they measure electrical conductivity, not moisture levels, ....... better to use a wooden 'tell'. It's pretty apparent you have an issue related to over-watering and the lack of oxygen that accompanies it. There is no way to determine if the root system is compromised by a pathogen w/o examining it. Look for dark, rotten roots or roots from which the outer covering slides off easily. At a minimum, you need to make sure you have watering under control. Using a 'tell' Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant. Watering in small sips leads to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor. In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water. Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'. One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue. Al...See More
tapla (mid-Michigan, USDA z5b-6a)
last yearMaria Elena (Caribbean - USDA Zone 13a) thanked tapla (mid-Michigan, USDA z5b-6a)
Tiffani Tesch
last yeartapla (mid-Michigan, USDA z5b-6a)
last yearlast modified: last yearYou're not really cutting against the grain at all. "Moist but not wet" is typically what nearly all houseplants prefer insofar as moisture levels in the root zone are concerned, so in that regard they aren't any different than most houseplants. They do like humidity levels of at least 50%, preferably higher. They also don't deal with perched water any better than other foliage plants.
As an experiment I put together a large humidity tray filled with peastone and filled it with water so the entire surface of the pebbles was wet. I placed a bonsai tree on blocks immediately above the tray - maybe 1/2" of separation and wedged a digital hygrometer in the branches. Imagine the setup below except the tray would be much larger and filled with peastone/water.
The humidity tray raised R/H only .4% (four tenths of 1 percent); so, most rooms will have much too much buffering capacity to allow a single humidity tray to make any meaningful difference in humidity levels in the plant's immediate proximity. It would take a good number of humidity trays in most rooms, or a humidifier (far more effective) to move the R/H level meaningfully.Al
Michele Rossi
last yearTiffani Tesch
last yeartapla (mid-Michigan, USDA z5b-6a)
last yearMaria Elena (Caribbean - USDA Zone 13a)
last yearlast modified: last yearWell, the last leaf just fell off this one, so it may be a goner. I'll place the pot on my 'triage table' and watch for new growth just in case but am skeptical. I have another similar wider leaf calathea that's doing great.
I'm in the Caribbean so humidity is very high and not an issue. I am also surrounded by beach, so the corrosive salt air is always a consideration. I used only rainwater after posting this and that made no difference. Since it's indoors, watering was every 7 to 10 days, depending on ambient temperatures and when the top 1'' of soil was dry. I NEVER water anything in 'small sips' ... I water to runoff and tip / bounce the pot to drain excess. I have had this plant 3 months and have only applied 1 tsp earthworm castings as a top dressing on month 2. There is no mineral buildup.
tapla (mid-Michigan, USDA z5b-6a)