exactly how much water and how often?
About 12 days ago, I bought a yucca with two canes in approx 11" black plastic pot - stands about 6 foot tall. Brought it home and drenched it (didn't know any better), but let it drain and emptied out the saucer so it wasn't standing in water. It sits right in front of a southwestern facing window but that window is behind a covered lanai. It does get bright sun on it for several hours each afternoon. I went to check how moist the soil was today and it is still very damp. Should I just not touch it and wait for the soil to eventually dry out? Then approx how much (in cups) and how often should I water? Thanks. Really want to try and give this plant a good home!
Good news is that yucca is really easy to care for, and the light you have it in sounds perfect. Even better news is that you're wanting to find out more about taking care of it. Your instincts are right on - you should not put more water on it until the soil dries out. Your next question is perfectly logical and frequently asked - how much exactly to water and how often. The answer is, I can't tell you that. The reason is that the amount of water is dependent on many factors - light, soil composition, size of pot, amount of roots, vigor of plant, and others - that are constantly changing.
The answer you need to ask is "how do I know when to water it again, and how much," and these questions can be answered.
The first and most important secret of keeping houseplants happy is to check the soil moisture all the way to the bottom of the pot.
You can do this with an electronic moisture meter, or with a thin wooden dowel or bamboo kebob skewer. For a yucca, the meter should read only 1 or 2 notches up from completely dry. The dowel, when you pull it up from the soil and run it between your fingers, should feel the slightest bit of dampness. If you move the plant away from the window to slightly less light (there should still be enough light that you can read,) the soil should read/feel completely dry.
Just always be aware of the soil moisture in the bottom of the pot, not just on the soil surface. The roots, after all, are in the bottom of the pot, not on the top.
Now comes the how much part, and that's pretty easy. You want to water enough to moisten the total root mass, top to bottom. Pour in enough water to get a runoff from the drainage holes - you should have 1/4 - 1/2" in the bottom of the drainage saucer. You don't need to pour this out, and the plant should not need watered again for a week or two.
Now you can answer the "how much" question for yourself - by measuring the amount of water you use, after 2 or 3 waterings, you'll have a pretty good idea of your plant's requirements. Make sure to check the soil moisture now and then, though, to keep up with possibly changing conditions.
This article has some more information on yucca houseplants: https://www.gardeningknowhow.com/ornamental/foliage/yucca/growing-yucca-indoors.htm