Hello Cynthia,

Oxalis can indeed go dormant, though we can't determine if that's what this plant is doing or not, as it would not put out new growth when doing so. Here is some information on growing Oxalis indoors and their dormancy needs: https://mastergardener.extension.wisc.edu/article/shamrocks-oxalis-spp/

It looks like this might be aged potting soil, and if so, the plant would benefit from it being replaced. Potting soil (or potting "mix") that is a year or more old can compress as it naturally and slowly breaks down. This compression slows evaporation and allows it to hold moisture, so the pot will take longer to dry out after each watering. It can also accumulate levels of salts (not just sodium but other minerals as well) from the water supply and any fertilizer used, and over time these residues can harm roots if levels get too high. By removing the old soil and replacing it with fresh, it can encourage new root growth (and therefore new leaf growth); either way, it improves conditions for root health. You can use any regular potting soil/mix for houseplants, or one labeled for use on African Violets or cacti/succulents, since both will have ingredients to improve drainage for moisture-sensitive plants.

Because Oxalis grow from little bulb-like tubers, the plant clump may fall apart a bit as it's repotted. That's ok - just set the tubers back into the new soil at the same depth they were growing before. Since it seems your plant may still be growing instead of going dormant, you can repot now or in spring. If it goes dormant anyway, just give it time and the conditions mentioned in the article link above, and it should re-sprout when it's ready.

Although pot type - plastic vs. ceramic vs. terra cotta - doesn't matter too much for houseplants, if a plant is staying too damp, using terra cotta can help as the clay absorbs some of that  moisture and helps it evaporate. In either case, it's important the pot has drainage and is only watered when the top inch or so of soil has dried, as Oxalis roots are sensitive to staying too wet.

With no or insufficient window light, the plant will decline over time as it is unable to feed itself by photosynthesizing. (We think of fertilizer as "food," but it's not food so much as it is like a vitamin supplement of sorts; the calories a plant needs as food comes from photosynthesis.) If no additional natural light is available, using a plant lamp (either fluorescent or LED) will help supply the light it needs, because ambient room lighting from desk lamps or ceiling lights doesn't provide enough light intensity or in the correct wavelengths to support photosynthesis. Plant lamp bulbs usually need to be within a foot of the leaves to provide sufficient intensity, but this will depend on the type used (and there are a large number on the market). Leaves that turn darker green or greener in general (such as when they're normally purple or yellow) often indicate that a plant isn't getting enough light, because the plant is generating more chlorophyll to try to make up for it.

We are not aware of Oxalis being able to root from leaf cuttings in water, so these are not likely to be successful. Instead, you can probably best propagate them by separating any tubers found in the soil when repotting, and potting them up separately to get more plants.

Miri