Lemon thyme is the perfect herb for any dish that requires the flavors of both lemon and of thyme. It can work as a seasoning for meat and you can add it to salads as well. The big problem with lemon thyme is that it is not a particularly easy herb to find. If your dish calls for lemon thyme and you are out of it, consider one of the lemon thyme substitutes below.
Your best bet: Thyme and lemon zest
Lemon thyme and common thyme (Thymus vulgaris) look almost exactly alike. Even an experienced cook can have a hard time telling the difference using appearance alone. Where the two differ is in the area of scent. Lemon thyme combines the earthy, woody notes of garden thyme with a lemony fragrance. The combination of common thyme and lemon zest can provide you with a similar effect. Not only will you get a similar flavor, your dish will look the same since there will be thyme leaves in it. If you decide to use this substitute, a ratio of 1 part lemon zest to 3 parts common thyme should provide you with a good approximation of the lemon thyme flavor.
A decent second choice: Lemon verbena
Widely used in Europe, lemon verbena allows cooks to flavor their food with an intense lemony aroma that is accompanied by mild ginger and floral notes. It is used in everything from ice cream to fish dishes. Just like lemon thyme, this herb can stand up to long cooking times without its flavor diminishing. In addition, you can make a lemon verbena infused olive oil or vinegar with the leaves or use them to make a tea.
Lemon verbena leaves can be tough so your options are to chop it very finely before adding it to a dish or use it like bay leaves, which means that you would add it whole to the food and then remove it before serving the dish.
Note that lemon verbena is known for its pungency. This means that when using it in place of lemon thyme, you should add it in small amounts and taste after each addition to find the right flavor profile.
In a pinch: Lemongrass
Lemongrass is a long, thick grass that contains an essential oil also found in lemon peel. It features heavily in food from Southeast Asia and is especially common in Indonesian and Malaysian cooking.
Lemongrass offers a bright, intense flavor that consists mainly of lemon, but with subtle hints of ginger as well. Similar to lemon verbena, lemongrass stalks can be quite fibrous and tough. In order to use them as a lemon thyme substitute, it will be necessary to chop or pound them to get a suitable texture. You can also opt for one of the many forms in which this herb comes. Those forms include dried and powdered lemongrass. You may also be able to find lemongrass essential oil.
Lemon balm is yet another herb with a strong lemon scent. It is typically used in much the same way that lemon verbena is used. Lemon balm pairs well with a large number of herbs and you can use it in many of the dishes that call for lemon thyme.