There is a widely held misconception that growers should withhold fertilizer in the winter, but that is pretzel logic and based on the assumption that you will be using a water-retentive medium that doesn't allow you to water correctly. IOW, the reasoning goes - because plants use less water in winter, water retentive soils need to be watered in small sips to prevent over-watering. Watering in sips causes a build-up of dissolved solids from fertilizer salts and tapwater, so you should withhold fertilizer. If you ARE forced to water in sips to prevent over-watering, withholding fertilizer is the lesser of 2 evils, but still an evil.
Every grower should strive to be at the point where either the medium they use or the tricks they employ allow flushing of the soil as you water. Flushing the soil typically resets the level of fertility in the medium to near zero after 3-5 waterings. Fertilizing after the 5th watering in winter with an appropriate fertilizer ensures an adequate but not an excessive level of nutrients plants need not only to grow, but to keep all plant cycles and processes orderly and balanced. A plant with an appropriate level of nutrients in the soil will always be healthier than a plant with deficiencies, toxicities (an excess of any nutrient), and unnecessary dissolved minerals, all else being equal.
To get back to your question, the answer is 'yes', you should fertilize in the winter, but to get to the place where you CAN, you need to be able to water correctly. That is no problem for plants in containers as small as yours. Here's a step by step guide that will allow you complete control over exactly what nutrients your plants get, and how much.
1) Flush the soil thoroughly by slowly pouring through the soil a volume of room temp water equal roughly to 10x that of the container size. That resets the level of fertility to near zero.
2) When you have finished flushing the soil, hold the pot over the sink. Move it downward toward the drain, then reverse the direction to upward. When you reverse the direction, water in the pot will continue to move downward and out of the pot. This trick puts Newton's First Law of Motion to work. The law says (in part) that an object in motion (water in the pot) will remain in motion and traveling in a straight line unless acted upon by another force. Keep moving the pot up and down until water no longer drains from the pot. This simple trick will remove all excess water from even the most water-retentive media, allowing you to use a medium that would otherwise be too water retentive to serve well as a grow medium. This is especially critical in shallow pots. Reason - the average commercially prepared potting medium supports about 4" of excess (perched) water. Which means that in a 4" pot filled to the top, the entire soil column would be 100% saturated ..... and you don't want to try to grow in something like that. Example:
3) You can fertilize immediately after flushing or wait a day or two. There is no need to withhold fertilizer at this point because your plant isn't physiologically "ill". It was simply damaged.
4) After you have flushed the soil and fertilized, each time you water you can drop a marble, button, or other object in the pot. When you're about to water for the 5th time, you can fertigate (fertilize + irrigate), remove the objects from the pot, and start the cycle over again. That way, you can keep track of when any plant needs fertilizer with ease.
5) Foliage-Pro 9-3-6 is a superb "go to" fertilizer for all your containerized houseplants. It has ALL nutrients essential to normal growth and serves as a complete nutritional supplementation program.
Using this method ensures a low level of nutrients perfectly balanced to the ratio at which the average plant actually uses the array of nutrients. For those who might argue against fertilizing in the winter, it's important to recognize that A) plants need nutrients for many reasons other than growth, and B) the level of dissolved solids (salts) in the soil will be lower than it would be if you simply stopped fertilizing in fall and continued to water in sips; AND, you won't need to deal with the artificial (antagonistic) deficiencies or and toxicities that come with watering in sips.
If you have questions, feel free to ask.
Al
