How do you know when your plant needs water?
When you water a plant, generally you pour water in from the top, pouring all over the top of the soil, not just in one spot. Even if you water from underneath, which many people have good luck doing, the object is the same — to thoroughly saturate the soil with moisture. After that, a certain amount of moisture needs to exit the soil through draining from the bottom, absorption by the roots, or evaporation into the air. This is called aeration, and different species need different levels of aeration — or, as I like to call it, the TML (target moisture level) for each kind of plant.
- Often people say “The soil needs to dry out more.” But that doesn’t mean the soil should get completely dry, with no moisture in it. Drying in this sense is a relative term referring to the aeration in the soil.
To know when your plant needs water, you test the soil moisture. That means, in one way or another, you find out how much moisture is actually in the plant’s soil, from top to bottom. Then, you water when the soil reaches the TML for your kind of plant.
So now we get to your particular plant — “at what moisture level should I water my Calathea?” As a starting point, Calathea and their relatives want a TML of slightly damp to moist. I would go toward the more moist side at the beginning; if you start to see brown tips on the leaves, let the soil get a bit drier between waterings. If you start to see the leaves looking curled and floppy, don’t let the soil get quite so dry between waterings.
Light is another thing these guys are fussy about — you can set them close to a north or east window, or a few feet from a south or west window — medium to medium-high light.
Humidity may be the major factor that makes Calatheas difficult — most important, they like high humidity. Often you’ll see “misting” advised, but misting is pretty much of an old myth. If you measure humidity with an instrument called a hygrometer, you’ll see misting doesn’t raise the humidity around the plant more than a couple of tenths of a percent, and that only for 10 or 15 minutes. You would need to mist every 15 minutes or so (which is what happens in greenhouses) to actually raise humidity. The best idea is to get a humidifier and run it close to the plant all day. Or keep it in a closed room, especially a bathroom with a big window, where you can turn on a hot shower a couple of times a day to steam up the air.
Calatheas are all rather particular plants, some varieties more than others, and there are maybe a couple of dozen different varieties on the market, in four different species. (Actually, the family name is Maranta [Marantaceae], and sometimes the genus from one to another is confused, but marketers seem to have settled on “Calathea” as a general term for most of the plants in the family.)
They like things a certain way, and aren’t interested in adapting to any conditions outside their preference — we say they have a narrow range of adaptability. In other words, you have to do all the work to make it right for them. But they are certainly beautiful, and your efforts will be well-rewarded.
