Dear Martha: Why do recipes call for unsalted butter? What is the difference between that and salted?

A: Domestic butter is available in two varieties, salted and unsalted. I generally think, as do many chefs and cooks, that unsalted butter tastes better than salted. Sometimes salted is way too salty for a recipe. With unsalted, you can control the amount of salt that goes into a dish.

Now, there are also many European-style butters that can be found in markets. The butter itself is so good, and the cream is so rich. I use salted for some recipes and unsalted for others. It's all about your taste. See which butter you like the most, and use that one. Just experiment.

Dear Martha: When I press flowers, they sometimes turn brown. What should I be doing differently?

A: Lush, plump petals can be a flower's greatest asset in the garden, but when the blooms are pressed, their natural moisture may cause discoloration and mildew. Of the many wild and cultivated flowers that are suitable for this preservation technique, thin and dry varieties, including larkspur, violets and pansies, yield the best results with minimal effort. Those with higher water content, such as orchids, require extra attention.

For the most beautiful pressed flowers, pick blossoms in the morning, shortly after the dew has dried, when they are in full bloom. Look closely at the petals to ensure that there are no insect holes or other blemishes. Arrange the specimens carefully between sheets of blotting paper or blank newsprint inside a flower press, a device with layers of corrugated cardboard between squares of wood, all of which is held tightly together by metal screws. Then set a heavy book on top for extra weight. (You could slip the paper and blooms between the book's pages instead.) Place the flower press in a cool, dry spot. If the flowers have thicker parts, the blotting paper should be changed daily for the first week, or until the sheets no longer seem to draw out moisture.

After the flowers have become stiff and brittle, which can take anywhere from two weeks to six weeks, gently remove them from the press, and store them between acid-free glassine sheets or in waxed envelopes, away from direct sunlight.

Dear Martha: I'd like to add an oyster-shell path to my garden. Is this a sound choice, and will it affect nearby plantings?

A: Popular in coastal areas, crushed-shell paths are an attractive and practical way to utilize a material that would otherwise be discarded. Oyster shells are commonly used, although those from scallops, clams and snails are also suitable. Because the shells are byproducts of seafood processing, this type of covering makes the most sense in regions where a shellfish industry is established.

Some farm and garden stores offer crushed shells in bulk, but purchasing directly from a seafood processing plant may be less expensive. Be sure to ask whether the shells have been steam-cleaned; if not, they might smell and attract flies. Even cleaned shells might retain a slight odor, but once they are spread on a pathway, a couple of sunny days should eliminate the smell. It might also be more cost effective to buy the shells in large pieces, which can be smashed to smaller foot-friendly sizes with a couple of passes under a lawn roller.

Crushed shells aren't appropriate for all locations. In general, they should not be used on paths or driveways that require snow removal, as many of the shells will be scraped up and lost during the winter season. Kneeling and walking on a crushed-shell surface with bare feet can be painful, so it may not be the best option for pool or play areas.

These shells do have an effect on the soil and surrounding plantings. The primary component in shells is calcium carbonate, which raises the pH of soil, making it more alkaline and less acidic. While large chunks of shells won't alter the soil as dramatically as the finely powdered ones specifically sold for that purpose, it is wise to avoid using them if the soil is already alkaline. *

Questions should be addressed to Ask Martha, care of Letters Department, Martha Stewart Living, 11 W. 42nd St., New York, NY 10036. Questions also may be sent by e-mail to: mslletters@martha Please include your name, address and daytime telephone number.