Hey Lillian,

It looks like overwatering to me. You can get brown spots from water stress among several other issues but when they’re surrounded by yellow it’s usually too much water.

It looks like its planted directly into the metal pot (which I assume has no drainage holes) or is it inside a plastic one with holes at the bottom?

Chloé

Concur it's likely over-watering and or a high level of dissolved solids (salts from fertilizer solutions [formerly used] + the dissolved solids that accumulate from tapwater when the soil is not being adequately flushed at regular intervals. Try using a 'tell' to 'tell' you when it's time to water instead of the "when the top inch or two of soil is dry' formula which almost ensures over-watering if the pot is more than about 5" deep. Also, the plant should never be allowed to sit in the effluent that exits the drain hole, and there should never be a pathway by which the effluent can make its way back into the grow medium. The bottom of the main pot should sit above all effluent that collects in a cache pot or collection saucer. Here is 1 way to correct:

This should be helpful (click me to see).

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

I like plants in the classroom, but as I recall, there is some uncertainty about the safety of this plant around children. You might want to check into that or at the least put it in a higher location like on top of the file cabinet or something.

I have a few dumbcanes and they are pretty easy to take care of but they do not like to be overwatered. They do well in dappled sunlight or medium to bright indirect light. I wait until the soil is completely dry to water them and use a soil moisture meter (Amazon for under 10 bucks) I agree with the others...look like this one has been overwatered and maybe some shock from replanting. The burning around the edges can happen if there is too much chlorine or minerals in the tap water, too much fertilizer, etc. You can check for root rot (the roots will be black/brown and soggy)...or just leave it alone and let it dry out all the way. Have the lead teacher put it in a corner in indirect sunlight where he/she doesn't see it all the time and see if it recovers. Give it at least a week. Best of luck on your new job. :)