Probably no harm in what you did, especially at that rate. I'm not going to imply that your plants can't benefit from some P but as they produce the N & K are bound to be the lacking nutrients. Tomatoes put a lot of K into the fruit and it is often lacking as the season progresses.

Since these are container plants, not in-ground plants, I think you'll find they will require regular weekly or every other week feedings like most all container plants do. That's because the nutrients wash out of the soil/container every time you water.

There is nothing wrong with what you have so far but I sure wouldn't count on them to provide all that is needed for very long. I have tried the spikes before and they tend to dissolve more quickly than you might think. And the ferts in the soil mixes, despite their claims, don't last long either.

What works best for me with all my containers is to use a 1/2 strength diluted liquid fertilizer once a week when watering.

Dave

I would buy something with higher N untill the plants are a little more mature.

In my 10 gallon containers with miracle grow potting soil I used miracle grow tomato food 18-18-21 once a week untill they started blooming now im using Green Light Super BLoom 12-55-6 but will be cycling it with the miracle grow to maintain K

Just make sure when you water, you water enough that you see water coming out from the drainage. Dont want anything like SALT building up in your containers.

I was using 14-11-25 last season for my container toms and peppers. Last year season started in april, finished in october, i was using only the mentioned fert and had abundance of fruit (started feeding when the first truss appeared). Ofcourse if you want that *little bit extra* you can always try to adjust ferts with different stages of growth but a simple balanced fert with a higher K will usually do the trick for the whole season. In late september, as it got cold, i did get some signs of phosphorous deficiency (purple veins), but at the time it had more to do with the temp of soil in container then with the actual phosphorous lacking.
Also, i've used that same fert for toms in the ground in garden and they didn't complain either :)