I live in Nebraska and have house plants. Lately, after watering them we can smell mold coming from the pots. Is there something I can do about it, I don't want to throw them away.
If the soil in your houseplants containers is extremely stinky then you definitely want to take some action to right the situation since good potting soil and/or compost is usually quite odorless. Let me suggest a few things to try and hopefully you will not have to get rid of any of your houseplants.
A good thing to know right off the bat is that most houseplants require significantly less water in winter. Even though our homes are kept warm through the winter, the sunlight during the day is significantly less and our houseplants are simply not as active as they are during the summer months. Many houseplants we consider evergreen still go through a dormancy period in winter. With limited sunlight the plants are still photosynthesizing, converting sunlight into energy in the form of carbohydrates, and growing, but at a much slower rate. As a result, your plants water needs are not as great as they are during the summer when the plants are photosynthesizing and growing at a much faster rate. In winter I still try and water with some regularity but I definitely apply much less water. Each houseplant has different needs, but in general I am always advising people to water slightly less but with greater frequency instead of drowning your plants and waiting until they are bone dry to water them again. Even some plants, like succulents for example, I might water only once a month in the winter, compared to once or twice a week during the summer. Excess water that is applied to the soil and not taken up by the plant then sits and runs the risk of promoting rot of roots and soil in your containers. So, first of all, if you don’t already, consider watering with less volume in winter.
With that being said, let’s address your plants more specifically. Hopefully the plants are not that large because what I would recommend next is to carefully pull the plants from their containers and inspect the soil, roots, and containers. Create a work space for yourself because you may very well make a mess, and if possible do this during a cloudy day or at night so the roots do not run the risk of being burned by direct sunlight. What you want to find is soil that is not overly compacted or claylike. When slightly moist, a good potting soil you should be able to ball up in your hand and when you release it, it should fall apart pretty easily. What you do not want is soil that has broken down so much that it is either like clay or like pulverized dust. Next look at your roots. Healthy roots are usually white or light in color and firm, rotting roots are dark or black, squishy to the touch, and probably not very good smelling. If you have root rot take a sharp pair of pruners or scissors and get the rotten roots out of there; they’re of no help to the plant. Lastly, make sure your containers have adequate drainage holes in the bottom. All houseplants require containers with drainage holes, even if they are considered water loving plants.
I’m hoping that all you really have to do to right the situation is repot some of your houseplants. Spend the extra couple bucks on a name brand potting soil (Schultz, Miracle Gro, etc) because the soil structure will be better than generic bags of soil that inevitably seem to frustrate me. If your containers do not have drainage, switch them to containers that do. If you have succulents or plants that require maximum drainage, consider a layer of small stones or pebbles in the bottoms of your containers to create an additional buffer for excess water not used by the plant. Usually you want to repot in spring, but it sounds like the plants will benefit from being checked out as soon as you can find the time. Let me know how it goes and if you need further help. Good luck!