First you need to consider what your purpose is in collecting plants, and what kinds of plants will serve that purpose. Many educational and craft uses of plant collections can be satisfied by cultivated plants and garden weeds. Before collecting plants in the wild, you should understand the legal issues of the ownership of the land and its resources, and the ethical issues of possible damage to wild plant populations and to endangered species. The California Native Plant Society's policy on collecting plants for educational purposes is well worth reviewing.
More and more the conservation ethic is to collect in the wild only when it serves a long-term research purpose, such as documenting what occurs in an area that is proposed for development, or discovering what grows in an area that has not been much explored. But these collections must be placed in permanent storage in order to serve their documentary purpose, and once in a scientific collection they can continue to contribute to science in many other ways.
WHERE TO COLLECT
It is legal to collect plants only with the permission of the owner of the property on which they are found. Government agencies that manage land generally grant permits only to researchers working for an approved institution, such as a university. Private landowners are often willing to allow judicious collecting if asked. Do not collect illegally.
WHAT TO COLLECT
If the plant is small, take the whole thing, roots and all, or even several of them. If large, get a branch about 10 inches long, with leaves, flowers, and fruits, if possible. A "sterile" specimen (one with leaves only) may be impossible to identify. Even an old empty seed capsule can be helpful if that's all you can find.
The date the plant was collected and the location as exactly as possible. Record anything that the specimen won't show, for example, the size of the plant, flower color, whether the plant is woody or not, etc. Note what kind of a place the plant was found, e.g., in gravel at stream edge, in shade under live oaks, in sidewalk crack outside Walmart. If you bring your plant to the museum for identification, we might want to keep it for the herbarium. If so, we will need all the information you can give for the label. If you will be preparing your own labels for us, they must be printed on acid-free bond paper.
HOW TO PRESS A PLANT
Place the specimen in a folded newspaper sheet. Write the date and collection locality on the newspaper. Arrange the plant so that all parts show, for example, don't get the flowers between layers of leaves. Separate the specimens with corrugated cardboard for air circulation (and blotters or paper towels to absorb moisture, if you like). Place the stack between boards and strap them tightly or place a heavy weight on top. Put the stack where there is good air circulation--it is air, not heat, that dries plants. Don't cook them.
Examine the plants daily and change blotters as needed. Remove plants from the stack when they are dry (stiff and no longer cool to the touch). You can kill insects in dried plant specimens by freezing them for three or four days, and keep them pest-free in a tightly-sealed plastic bag.
For over four hundred years people have preserved plants for study by pressing and drying them. A collection of such dried specimens is called an herbarium. Plants that have been thoroughly dried and well mounted, and are protected from moisture and insects, will remain intact essentially forever. Linnaeus's collections, made in the 18th century, are still used (very carefully) by researchers today.
A specimen consists of a dried plant, or piece of a plant, or several small plants of the same kind. It comes sandwiched in a folded sheet of newspaper (the same one in which it was pressed and dried). In order to display its parts for study and to prevent damage in handling, it should be mounted.
PAPER FOR MOUNTING
Herbaria in the United States, and most other countries, use a standard size paper (11.5 by 16.5 inches) for mounting plants. We use University of California type, a medium-weight acid-free buffered paper.
We use a neutral-pH formulation of PVA (polyvinyl acetate: a white glue like Elmer's) for mounting specimens. We dilute it with water for general mounting and use it full strength for specimens that need to be more firmly glued, such as a woody branch that only touches the sheet in a few spots.
ARRANGING THE SPECIMEN
First, take some time to look the specimen over. Clean off dirt, dead insects, bits of other plants, and so on. Decide which side should be up. See what parts are on the plant that must show in the finished specimen.
The specimen should be mounted in such a way that all its parts can be studied. Both sides of the leaves should show. It may be necessary to trim some parts off to make the specimen fit on the sheet or to expose important plant features.
The label is placed in the lower right corner of the sheet. An envelope for small loose parts or seeds may be folded from a quarter sheet of acid-free typing paper and glued anywhere it will fit.
GLUING THE SPECIMEN
We usually use the "glass plate" method of mounting plants. A thin layer of glue is spread on an aluminum cookie sheet (traditionally a sheet of glass). If using white glue, some water can be stirred in to dilute it to the consistency you want.
The specimen is first arranged on the paper as it will be glued, and all necessary cleaning and trimming is done. Piece by piece the plant is placed into the glue, making sure all parts have touched down and picked up glue. It is then lifted and blotted on newspaper, and placed on the paper. A paper towel is gently pressed against all parts of the plant to squeeze out and blot up excess glue and to push the plant against the paper.
A thin layer of glue is spread on the back of the label with a palette knife, and the label smoothed into place and blotted.
Another method of gluing is useful for tricky specimens (like wispy grasses, which may gloop together in glue) or recalcitrant parts (such as roots or fuzzy leaves, which often seem glue-repellant). The specimen is arranged on the paper and held in place with weights. Then, working from the roots upward, the weights are removed and glue painted gently on the under side of the plant with a palette knife, and then blotted. The weight is then replaced before moving on to another part of the specimen. The weights are removed before placing the specimen for drying.
ALLOWING GLUE TO DRY
The specimen is covered with a sheet of waxed paper so the glue won't stick to anything else. A square of cardboard is placed over the label to hold it flat while it dries. Padding may be added to press down the flatter parts of the specimen if there are bulky parts like stems or fruits. A sheet of cardboard may be placed between specimens to distribute the weight. A board and a weight (we use a rock) top off the stack. The plants are left to dry overnight.
Specimens that are well mounted using archival materials will last essentially forever, but only if protected from "agents of destruction" such as molds, light, and insects. They should be stored in a tightly-sealed box or cabinet. No pesticides need be used if no insects can get into this space.
Insects can be killed by freezing the specimens (after the plants are dried, but either before or after mounting) at a temperature of -10° F. for three days or longer, preferably in a freezer that is not self-defrosting (since these have cycles of warm temperatures). Specimens should be placed in a plastic bag first, and left in the bag until they reach room temperature after coming out of the freezer. Everything should be frozen before being placed in your storage space, and if an infestation is found, everything should be removed and frozen, and the space thoroughly cleaned before replacing the specimens.
The specimens of Calochortus albus pictured at left were collected in 1881.
The same techniques we use in the museum can be used for projects like decorated notecards and framed arrangements of flowers and leaves. Such projects typically use separate small flowers and leaves, which are easier to press and dry than bulky scientific specimens are. They may be successfully dried between the pages of an old phone book. Press them inside a fold of paper as described earlier, so that you have a way to handle the flowers after they are dry. You can lay dozens of small flowers or leaves on a page. Press them down with a finger to make them lie flat before you close the book on them (they're going to be squashed anyway, remember).
Do not go to wild places and collect native flowers for these purposes. There are many suitable plants you can use without damaging the environment: look at garden weeds, garden flowers and trees, and even the grocery store! Carrot tops have lovely delicate foliage. Flower clusters, like those of bottlebrushes and marigolds, can be separated into their individual tiny flowers. Many weeds, like wild radishes and grasses in lawns, have very pretty flowers. Look around you and think small! You'll find plenty of material to use.