If fertilizer was actually plant food, it could be said that a plant's diet consists of salts, a 'salt' being the product of the interaction between an aid and a base (vinegar and baking soda, e.g.). If the soil cannot be flushed regularly, the issue is two-fold. 1) The salinity of the soil solution increases over time, which makes it increasingly difficult for the plant to absorb water and nutrients. 2) The ratio of nutrients in the soil solution (each nutrient to the others) will become increasingly skewed. This is a critical factor because an excess (toxicity) of one nutrient can cause the plant difficulty in sourcing one or more other nutrients. Examples: A) Using a high-P(hosphorous) fertilizer in containers can cause a deficiency of copper, potassium, copper, zinc, and especially iron. B) Dosing with magnesium just because someone on the internet suggested it's a good remedy for chlorosis, can cause an acute deficiency of calcium.

So, for any self watering container, it's important to use a fertilizer that closely mimics the ratio at which the plant actually uses the nutrients. This helps to keep o/a salinity low because you'll be able to use less fertilizer; and, because the nutrient array is provided at the same rate at which the plant actually uses the nutrients, skewing of the % of nutrients in the soil solution is minimized. This is true whether you use a synthetic soluble fertilizer or rely on organic soil amendments (often referred to as fertilizers) as your nutrient source. It is MUCH easier, more reliable, and it affords a greater measure of control, if you rely on soluble synthetic fertilizers for container culture. IMO the best choice for a 'go to' fertilizer for containerized plants is Foliage-pro 9-3-6. It has all nutrients essential for normal growth in a ratio that minimizes excessive salinity and skewing of nutrient ratios.

IF, you can separate the two pots so you can flush the soil regularly (at least once a month), it will solve the build-up/skewing problems.

Questions?

Al

Thank you Al for your very knowledgable reply. I can easily seperate the inner and outer containers, but the inner container is just like solid terra cotta. There are no drainage holes. So would I be able to ever actually flush that, or would I have to repot instead?

It's very easy to drill a hole in the bottom of a terra cotta pot, which would allow you to flush the pot regularly. There simply is no effective way of managing salinity and fertilizer ratios w/o a regular flush. You could also buy a pot with a hole already in it (which fits your cache pot) and go from there.

I'm retired now, but I owned a contract glazing corporation before I retired. Drilling holes in glass, ceramic, granite, stainless steel, cast iron, ....., and other very hard substrates is an every day occurrence for this type of operation. Something I wrote for container gardeners based on >42 years of experience drilling hard materials:

Drilling holes in pots

The 2 types of drill bits most appropriate for drilling holes in pots are diamond core bits for the highly vitrified (hard material - baked at very high temps - glass, ceramic, ......) pots, and a drill with several names for drilling clay pots fired at low temps, such as terra cotta. That (carbide) drill is called a 3-point drill, spear point drill, or a spade drill, seen here:

For the hard stuff, diamond core drills are best, though the 3 point drill will drill the hard stuff, too. Both are available in many sizes, with bits sized 3/8 or 1/2” best for pots.

You can buy either type at big box stores, and they're not that expensive, but you won't find a 'set' of diamond core bits worth buying for $9. The bits last a long time, depending on quality and how you use/care for them. They are best used with a steady stream of coolant from a squeeze bottle (contact lens solution bottles work great for this) or with the work surface barely submerged. IE, put the pot upside down in a tub and fill the tub with water until it just covers the work surface. If you use a spritzer or squirt bottle, a 50/50 mix of antifreeze and water is an excellent coolant, and soapy water is better than plain water but not as good as the antifreeze mix. The coolant keeps the tool from over-heating, and in doing so, increases the life of the tool substantially - like triple or quadruple the number of holes you can drill. While drilling, apply very little pressure, just the weight of the drill motor with you providing only guidance is sufficient. Drill at medium speed – somewhere around 1,600 rpm. NEVER use either type of drill mentioned above without a lubricated coolant. The heat will cause thermal shock and fracture in glass and ceramics and heat build-up will destroy the tool.

Regular masonry bits are "ok" for drilling terra cotta or cement (you can make them work), but inappropriate for anything harder. The right tool makes everything easier.

Al

The pot you have is often called a "violet" pot as a lot of people like to grow African violets in these type of self-watering planters. You can put the water with fertilizer into the reservoir (outer) pot and it will get soaked up by the plant. Or you can use a pellet-based fertilizer in the soil.

@kujen said, "I feel like liquid fertilizer will build up salts, and I cannot flush it since there is nowhere for the extra water to go". So there's no confusion, both suggestions would work well as long as the pot can be flushed with regularity, but in a case where the set-up doesn't lend itself to being flushed, Kujen would still be left with issues related to increasing salinity and skewed nutrient ratios.

Al