Lots of herbs (maybe all of the Mediterranean ones?) don't like fertilizer. It reduces the pungency of their...herby-ness. :) and it just doesn't make them grow well.

I know with thyme, especially, you stick it in poor soil and fertilize it maybe once, at the end of summer? Remember the conditions they are from. Thyme, for example, grows natively on cliffs and between rocks!

A natural nitogen may help some. Your wanting to get as much green as you can.

Most of the popular culinary herbs don't want or need fertiliser - they prefer their soil poor. Potted plants, however, will need not to be ignored - they are high maintenance and you'll need to fertilise those from time to time as the nutrients leach out (this doesn't happen in the garden).

I find that compost is a good fertiliser. I have only a teensy courtyard garden, so no space for a compost heap - so I buy it in bags. Whenever the soil level in pots gets a bit low, in goes a handful or two of compost. And while I'm at it, I toss handfuls of it hither and thither over the garden.

Even changing the potting soil from time to time will be enough for many of your herbs - you'll do this for things like mint or lemon balm on a regular basis.

Basil and chillies are greedy plants and will need more fertiliser than others. I suggest for beginners to use a slow-release fertiliser in pellets according to manufacturer's instructions around basil.

"hither and thither"? LOL! LMAO here!

I've enjoyed the use of "hither and thither"....!

I have Thyme, Sage, Greek Oregano, Rosemary, Italian Parseley, Basil, Mint and Lavender in pots. Except for Lavender, everything else I have fed Fish Emulsion regularly during growing season.

In my experience, it has not introduced pungency to the flavors. In fact, once in winter I bought mint since my mint had lost all its leaves. At the checkout, a woman behind me commented on the smell of the mint; however when I actually cooked with it, I had to add a lot more than my home-grown mint (ie store one had less flavor).

IMO, plenty of sunlight + regular feeding works wonders on herbs. I have heard somewhere that you should not overwater them; and I usually water them once every two days during summer.

I agree with homey-bird about the sunlight. Without it, and plenty of it, the plant will not produce the essential oils which give herbs their flavour and aroma. For the Mediterranean herbs, the more sun, and the hotter, the better.

Potted plants will always need more fertiliser than those in the garden, because nutrients leach out quickly. However, in the garden, fertiliser for most of these herbs just isn't needed or wanted by the plants.