Assuming it is really tiny, I would use liquid fertilizer. Just make sure to never fertilize a dry plant - always water it first, and then apply some liquid fertilizer for "dessert". Needless to say, it is better to fertilize frequently at low strength.
If you want to use organic fertilizer, you can make a "tea" with it, and apply fertilizer that way. Just note that fertilizer made this way can go bad/funky pretty fast, unlike Miracle-Gro (or similar chemical liquid ferts) which you can mix up in advance and keep around indefinitely. If you want to grow moss, or delicate companion plants like miniature ferns, organic fertilizer tea has given me great results.