The length of time flowers last after being preserved depends on the method of preservation as well as storage after preservation. A wedding bouquet, air dried and kept for 35 years in a glass jar, still has intact rose buds, yet with brown petals instead of their original color. Had the dried flowers been allowed to collect dust for three decades, they would have probably lost their petals years before.
A factor to consider when estimating how long flowers might last after preservation, is the condition of the flowers before preservation. Regardless of the method used to preserve the flowers, for optimum results the flowers should be fresh, at their prime or slightly immature and perfectly formed. Anything less will deteriorate quicker.
Not all drying methods are appropriate for all flower types. Most flowers will gradually fade after preserving. If stored in a humid area or carelessly handled, the flowers may last less than a month. Some properly dried flowers last years in a floral arrangement or wreath, yet quickly deteriorate when exposed to sun, dust or rough handling.
One of the simplest and straightforward at-home methods of flower preservation is air-drying. Generally, flowers can last for years. Air-drying involves hanging a bouquet upside down in a warm well-ventilated area for about a week. While drying fades the flower's color, drying the flowers at too hot a temperature fades the flower's color more rapidly. Air-drying dehydrates the flower, so that it does not suffer normal decomposition.
An old-fashioned method of flower preservation involves pressing the flowers between absorbent sheets of paper before covering with a heavy object. The flowers dry out and are suitable for projects like card making. Some artists use the pressed flowers to create floral pictures. If placed behind glass the flowers can last for decades, yet gradually lose their color. When displaying the finished floral picture, if placed near bright light or heat, the flower's disintegration excels.
Many craft enthusiasts use a desiccant, such as silica gel, to dry out flowers. This involves covering the cut flowers with the descant and storing in a box, until the flowers dry which may take one to three days, depending on flower type. These types of flowers are often use in flower arrangement and may last for years, depending on how they are stored and used.
Freeze-drying is not typically a home preservation method, as it requires expensive equipment. Freeze-drying produces more lifelike results, compared with other drying methods. This involves freezing the flowers and then removing the solid liquids through a vapor-removal process. Professionals offering the service often claim properly stored flowers that have been freeze-dried can last a lifetime.