In the process of drying herbs, blossoms, and foliage for use in potpourri, some of the fragrant oils evaporate, along with the moisture, and are lost. Essential oils, fragrant essences extracted from the plants, are often added to pot pourri not only to strengthen the fragrance, but to make it last longer.

These oil are very concentrated (unless they have been "cut" with less expensive oils), and only a few drops are needed to boost the natural scents in a potpourri. It is better to spend more money for the best oils than to use diluted oils.

In choosing the oils to add, it is best to stay as close as possible to the  ingredients in the potpourri. Some oils, such as rose and bay, will intensify and bring out the fragrance of other plants as well as their own.

These are both good general purpose oils. Others, such as lavender and citrus oils, are distinctive and tend to predominate. Beginners who can purchase only one oil should choose rose, adding others as their repertoire of ingredients expands.

It is best to avoid fruit oils, except for citrus, since such fragrances as strawberry have a strong, artificial smell that becomes tiresome very quickly.

The amount of oil to use depends upon its strength, the amount of the potpourri, and the use for which it is intended. Potpourri that will be enclosed in small sachets need to be stronger in oils than those that will be in a large jar. Unlike enclosed blends, sachets are open to the air at all times, so the scent dissipates more quickly. Three or four drops per pint of plant material is usually about right for potpourri that will be in a covered container.

The oil may be dropped directly in to the potpourri mixture or it can be mixed with chipped orris root first. The latter method assures that it will spread more evenly throughout the potpourri and also helps to preserve its fragrance longer.

When oils are first added to the potpourri, the mixture will have a raw, sharp smell. As it has a chance to blend it will mellow and become smoother. To help this process, a potpourri should be kept closed for at least two weeks after it is made, and stirred or shaken each day.