My preference is to use controlled release fertilizer with any potting mix and also use soluble fertilizer once the plant starts growing vigorously. I used to use Promix and if I remember correctly the directions say to begin fertilizing right away. It stands to reason that no store bought potting mix would have a significant amount of fertilizer in it because the fertilizer would be activated by moisture. Some of these bags sit in a warehouse, or outside, for months or years. One of the big myths of the consumer gardening industry is that a bag of potting mix has everything you need to grow a healthy plant for months. What they have is enough for the first few weeks.

I don't use CRF, just regular organic fertilizer which breaks down more slowly anyway, but I'd probably just sprinkle it on and rake it in. Weird that the label is no help. Good to avoid spray on anything when having a butterfly garden--don't know how that stuff can affect butterflies and caterpillars.

I grow many grasses, including 'Hameln,' in containers. The only fertilizer they get is a soak with very weak compst tea, as well as foliar spraying, 1 or 2 times before their flowering season. They also get re-potted every 2 years, with new potting mix, which will include a small amount of bone meal. You don't say what hardiness zone you are in, but you should be aware you lose up to 2 zones with container grown plants. This means if you are in zone 5, your plant should be hardy to zone 3 to survive winter outdoors. 'Hameln' is hardy to 4 or 5, depending upon who you listen to. It might be a good idea to overwinter them indoors.

I should also add that liquid organics are not considered 'slow release' either. They are immediately available and you will have to reapply periodically. Dry or granular organics ARE slow release as there is a time delay involved in the processing of these by the soil biology before the nutrients are converted into a plant usable form. But as stated previously, these are not at all efficient for container gardening. Bit of a catch-22 situation :-)) ETA: I didn't see your last post before posting this. Good that you have a back-up when the vegan organics don't do the trick!!