Therapeutic efficacy varies during different times or seasons of the year. The constituent and active principles vary quantitavely at different seasons of the year and the majority of plant materials are usually best collected during the dry season, when the herbs are at peak maturity and concentration. Dry as quickly as possible, away from bright sunlight, to preserve the ingredients and prevent oxidation.
Roots and rhizomes: Best collected October to February, when the plants are more vigorously storing food in their underground organs.
Leaves: The most opportune time is when the plant is about to bloom.
Flowers: Buds are preferred, best collected in the morning after the morning dew has evaporated; flowers, just before or shortly after opening. Dry the herbal materials as quickly as possible.
Bark materials and stems: Generally, best gathered in summer time. When the climate is warm and humid, the bark of any plant usually contains richer nutritive substances including the medicinal metabolites. Preferably, barks and stems should be removed only from fully grown plants. Do not remove all the bark or a band of surrounding bark.
Fruits and seeds: Fully ripened fruits and mature seeds are preferred. Collection of pod fruits is done in the morning to avoid unnecessary opening up of the fruit wall to the detriment of losing the seeds. Turn the fleshy fruit frequently for even drying.
Whole plant: When the whole plant is desired, it is advisable to harvest the plant at the time when the flowers are all in bloom. Old and withering plants are less effective when used as a source of drugs.

Information about the whereabouts of the plants, especially the rare ones, can facilitate the search for them. It saves both time and energy. Low altitudes probably range from sea level to about 300 meters; medium altitudes from about 310 meters to about 1000 meters; and high altitude from about 1000 meters and up.

Many medicinal plants are seasonal, some not easily accessible, available only in deep forests or mountain peaks. Such restrictions necessitate ways and devices to store them for future use. Dirt and other foreign substances should be removed. If washing is needed, it should be done quickly to minimize deterioration and loss of active substances. As a rule, all parts of the plant collected should be dried as soon as possible to avoid unnecessary waste of the drug materials through natural processes of denaturation, decay and fungal attacks. Some commonly used storage methods used buy the Chinese are as follows:
Sun-drying method: Spread the herbs over the dry beaches, patio or benches that are under the direct scorch of the sun until the materials turn dry and brownish.
Shade-drying method: Some plant materials are preferably dried under shade at room temperature by wind action- because of heat-labile substances that they contain. As such, free circulation of air is important. Drying processes should be shortened, if higher drug contents are to be sought for. Floral and fruit materials should be dried by this method.
Heat-drying method: Some materials may be placed over an oven and dried under the intense heat released or under regulated soft heat. Plants that contain high sugar and starch are best preserved by this method. In places where the rain falls throughout the year, this method is strongly recommended.
Other Special Methods: Succulent materials are usually washed first in boiling water or steam-cooked in a container before actually drying it. For spiny and hairy materials, remove the unwanted appendages. Some plant materials (ex. succulent materials) may require cutting or sectioning before drying. In general, the moisture content of the dried plant materials should be less than 10% before storage. Moisture content higher than 10% usually leads to growth of microorganisms and pest infestation with consequent drug deterioration.

The dried plant materials should be placed in plastic containers or tightly covered bottles; brown colored bottles are preferred as they minimize deterioration due to sunlight. Dry charcoal (separated from the medicinal plant) may be placed inside the bottles to absorb moisture. The storage place should be dry, well-ventilated, and spacious, lest fungi and insects may invade rampantly. Drug materials (dry ones) after proper processing can be kept in large open wooden shelves. The humidity of the storehouse should then be as low as possible. Materials rich in volatile oils are advised to be kept in airtight containers. Otherwise, their efficacy will decrease as time passes by. If all factors are favorable, the prepared drugs can be used even after years of storage.

Preservation and Conservation
Know how to preserve and conserve plant sources. Complete depletion of all medicinal plants founds in an area should be avoided. Once collected, all the materials should be processed at once for long storage. Well planned activity in the collection of plant materials will always prove to be economical and advantageous in the long run. Cultivation of these medicinal plants should be tried in places where conditions favor because cultivated plants contain higher percentages of the medicinal principles desired.

A Manual on Some Philippine Medicinal Plants (How to Collect Medicinal Plants), U.P. Botanical Society, 1977
Herbal Medicine (Technoguide Volume 1), Central Visayas Technology Packaging Project, 1988
Complete Guide to Medicinal Herbs, DK Natural Health, Penelope Ody, 1993