Question
I recently found what I believe is a Calathea out by the dumpster in my apartment complex, and rescued it. I've done my best to keep it well watered, and misted, but even the new leaf (that opened after I rescued it) has burnt brown spots. Is this due to the time in the sun, or am I still doing something wrong?  
I did not change the pot, but I did replace the soil immediately, as it looked like the soil was completely exhausted.
I am sending photos to your email.

Thanks!

Answer
Hi Odessa,

So much has happened to this plant, that is is hard to know just what it is reacting to.

The soil of abandoned plants gets very dry and looks like it is exhausted. In fact, that is rarely the cause and so doesn't warrant replacing the soil, in any case. The soil simply needed a good soaking and perhaps the addition of some fertilizer. Replacing soil invariably does more harm  than good. This is because the tiny root hairs are usually torn on the process and those root hairs do most of the work.

So the brown-spotted new leaves may be reacting to the soil replacement. Or it may be a reaction to roots that were previously damaged by neglect. Who knows how it was cared for before it hit the dumpster?!

All of that said, let me describe to you how best to care for a Calathea.

Calathea likes lots of bright indirect light. Direct sun will burn the leaves. A north windowsill is best.

Water thoroughly as soon as the surface of the soil feels slightly dry. Never let the soil dry out deep into the rootball, but avoid keeping the rootball saturated. This is a tricky balance between over and under watering, but it is an important key to keeping the plant looking good.

Calatheas do not respond well to hard water or to softened water. Both have excess mineral salts that damage leaf edges. If your local tap water is hard or softened, then switch to filtered, distilled or rainwater. For the same reason, restrict fertilizer severely; use it only at half strength during the warmer months when it is growing vigorously.

Related to the watering is the soil quality. The soil should be a very light and porous mix that maintains lots of tiny air pockets. These plants rarely need repotting, so it is best to leave the soil as is.

Calatheas do not like dry, heated indoor air. Misting does not help raise humidity significantly. A portable humidifier placed nearby is best. As an alternative, place a large pebble tray underneath your Calathea and keep it filled with water. They require warm temps at all times above 60 degrees.

Please let me know if any of this is unclear or if you have any additional questions. If you would like to e-mail me some photos, I may be able to provide some additional insights.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

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