Slow Growing Santolina Seedlings

I purchased the seeds for dwarf santolina from your store. I understand this herb is pretty difficult to find in Canada. I did plant some seeds in a pot and have a few small plants. They are outside on my patio, in a sunny location, watered regularly, but not growing very much at all! What can I do to encourage the growth? Is the herb a perennial? Do you suggest I plant it in the garden or leave it in a pot? I live in toronto.

Santolina is a slow growing herb. It is a slow and sporadic germinator, and after germination, the seedlings take more than a month to reach 1-2 inches in height. Santolina is a tender perennial in Toronto, so between now and next spring you will need to grow the seedlings in pots which you will bring indoors before the killing frosts in fall. For the summer and early fall it is fine to keep the seedlings outdoors where they are getting direct sun. The more light that they get the more they will grow and the growth will be healthier, and more compact. You will need to provide a bright window with as much direct sun as possible while indoors. You may need to provide supplementary light also.
You don't say how big the seedlings are, but likely they are still only an inch or two tall, and likely they need to be transplanted. If you haven't already done so you should transplant the seedlings into individual pots so they have room to grow. Santolina must have a well-drained soil.
Next spring after the frosts are over you can plant your plants in the garden. Once in the garden they will grow more rapidly and develop into nice low compact bushes. Santolina is famously grown as a miniature hedging plant in herb gardens because of its compact growth habit, its striking grey colour, and its tolerance of regular clipping. But because it is not winter hardy in Canada you will need to bring it indoors each winter if you want keep the hedge from year to year. For large hedge plantings it is best to keep the plants in a cool, but heated greenhouse over winter.