Unless your containers are very large it is hard to do organic in containers. Not only is the NPK in organic lower than synthetic, most organic fertilyzers are not available to the plants until they are converted by the soil organisms. So if your NPK is 3-2-2 less than half of that is available nitrogen. Read the label for percent of nitrate, that is the only fraction with available nitrogen. Most of it is slow nitrogen that might take up to 2 years to release. All of the synthetic nitrogen would have been available to the plants immediately when they needed it. You will have to supplement your heavy feeders especially with fish emulsion, blood meal, AACT, manure and compost teas weekly. The purpose of organic is to feed the soil and the soil should be able to sustain the plants. If you have to add more than 10% supplemental fertilizer then you are feeding the plants not the soil.
Some people do put soil in containers but in the long run, it gets hard and does not work well. Compost in containers, some people have good luck with that, but I cannot put more than a handful of vermicast in a 5 bucket container without getting into trouble. As you have noticed, containers leach nutrients so they have to be fed more often than in the ground.
Peas don't need a lot of nitrogen and cucumbers are not the heavy feeders that tomato and squash are. They need to be fed fish emulsion and kelp meal probably every week. The cucumbers will need it too. Yellowing on lower leaves, stunted growth and if the green is paler than your parents plants usually mean lack of nitrogen. The containers sound like they drain well so they should not be over watered. You should keep the mulch away from the stems to keep it from rotting.
Organic in small containers is hard because there is not a large population of microbes in the soil, especially new soil. The first crops should ideally be low requirement legumes and herbs that give the chance for the soil ecosystem to build.
If you choose the right container or you build the right kind of garden, organic can work better.
Using rotting logs at the base of the planter is hugulkultur
Incorporating a compositing basket in the planter keeps feeding the soil. Usually keyhole gardens are round, but they can be rectangles. The layering of the materials are important to making it work. A couple of scoops of garden soil will provide the starter organisms. The first crops should be low nutrient users like legumes. And organic fertilizers need to be applied often especially when plants are young and growing.
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