i keep a gallon milk jug with a common water soluable fert ... diluted according to the label ... and then i just splash some of that into the watering can with every watering .. .. so that i use a highly diluted fert .. with every watering ...

something like this.. 1.5 pounds ought to last you a decade or so .. lol ...

https://www.walmart.com/ip/Miracle-Gro-All-Purpose-Plant-Food-1-5-LB/16828998

there is no real magic about brand names.. and all that snake oil claims they might make ... imo.. just choose the cheapest general fert labeled for flowers and plants ...

but i would stay away from sticks.. spikes... etc.. and personally i just wouldnt waste the money on expensive time release fert.. for 2 pots ...

i think the container i am using.. dad bought at k marts about 20 years ago.. lol ..

ken

Yes, use any water soluble or liquid fertilizer - MIracle Gro is perfectly good but any other will work equally as well. Dilute to half strength and water it in weekly ("weekly, weakly")

I agree....and there is no 'best', though some would like to tell you otherwise.