It may need a bigger pot. If the leaves drop off and are turning a little yellow first, it could be too much water. I would avoid using fertilizer on most herbs, as it tends to leave a chemical taste and also makes for excessive growth which isn't as flavorful for the foliage. It does love sun and can do quite well. Because its starting to show signs of stress now, it could be due to it being forced grown in a controlled greenhouse.

Put it outside in full sun, and in the garden if you can. Do not fertilise it at all, and don't even water it. Just give it a good drink when you transplant it, then forget it - unless you have very sandy soil which doesn't hold the water. Even then, a good deep watering once a week, even in the heat of summer, should be enough. Rosemary likes poor soil, and if your soil is either sandy or clay, just dig in some compost before planting.

Thanks to both of you for your helpful comments!

And do a check for spider mites, as well. Mites are very fond of rosemary, darn it all. Perhaps more so, when the plants are container grown.

That fertilizer could have cause some problems, too. It's fairly likely that the rosemary already had some slow release fert. in it. Triple 10 is fast acting and very apt to burn a container plant, unless you used very, very little.

Perennial plants like rosemary (let's consider it a shrub) can be planted like woody plants, without adding amendments of any kind to the planting hole. That practice has been found to be detrimental to the long term health of our plantings. I've established mine in hard, red clay and it's about to take over the garden.

Rosemary has several types and the ones I grow here die over the winter and never return.

Hi i also having my rosemary dropping his needles and turning
brown why is it to much humidity?
It has sun only in the afternoon.the rain here is a lot shall i put it away from too much rain or id it symply the need of changing pot
although my pot is about 3 0cmin diametre.
I would appreciate your hel.p