Collecting Plants: A Pressing Project

Making Herbaria, Field Guides, Gifts

When European explorers struck out in the 16th century to discover parts unknown, they often returned with samples of plants they'd met along the way. As this collection of treasures soon exploded, botanic gardens were hard pressed to keep living samples of the whole lot. So botanists devised a solution: create a collection of pressed plants.

After all, scientists wanted to compare their discoveries, identify new plants, and document the diversity and distribution of plants on Earth. The system they designed includes carefully pressing plants, mounting each specimen on a sheet of heavy paper, and creating an accompanying information card. These feature such details as when and where the plant was found (and by whom), its habitat, and the common and scientific names (if known). These plant libraries, which scientists still use today, are called herbaria.

Consider engaging your students in gathering, identifying, and pressing local plants (or parts, such as flowers). They might then create scientific-style herbarium pages, bound into booklets, or design a field guide to the green denizens of the class butterfly garden, schoolyard, or neighborhood. (Schoolmates and visitors can use the field guides to tour the site and identify plants they encounter.) By focusing on specific plant categories — those with medicinal uses, native trees, or plants pollinated by bees, for instance — you can enhance thematic studies. Flattened flowers and interesting leaves can also inspire a host of art and gift projects, including notecards, placemats, and decorative candles.

As your young scientists tune into what's growing around them and compare flowers, leaves, and other plant parts from different species, they will hone observation and classification skills.You can encourage such plant collecting adventures through the season, or integrate them into a shorter unit.

Materials

• For each plant press: squares of corrugated cardboard, sheets of newspaper and/or blotting paper (check at craft stores), and 2 plywood or other boards, all cut to the same size; something to bind the stack (belt, bungee cord, or a heavy rubberband) or weight it (heavy books or bricks).
• For mounting collections: sheets of white paper (card stock or other heavy paper works well), thinned Elmer's white glue, tweezers (optional), clear contact paper (optional).
• Miscellaneous: scissors, field guides, binders or folders for students' collections, journals, or field notebooks. If you plan to make pressed wildflower cards, you'll need card stock paper and clear contact paper.

In the Field

1. Make a plan. A scientific herbarium collection usually features plants that grow naturally in a region. If your students want to create a field guide to their butterfly or herb garden, or collect flowers for an art project, they need not limit themselves to native plants. Decide on your purpose for collecting and pressing plants, then discuss as a class what types of plant parts to gather (wildflowers or tree leaves, for example) and where to do so.

2. Get out and gather. It's best to collect plants for pressing when they are free of dew or rain. Students can use scissors to snip flowers, leaves, or entire plants. If they are creating scientific herbaria, they'll also want to collect some roots. Flat flowers tend to press better than bulky ones. Invite students to experiment with different types of flowers and plant parts (by removing and pressing petals of larger flowers, for instance). If plants are abundant, suggest that students collect several flowers from a species so they can display front, back, and side views. Collecting flowers at different stages of bloom can also inspire a more interesting display.

Pick with Caution! Never collect or disturb any plant species that may be endangered or protected. Learn your state laws by contacting a natural resources agency. It's a good idea even with non-protected plants to use the following rule of thumb: never pick a plant unless you can see at least six in the area. Also, always get permission from the owner of any property on which you intend to collect plants.

To keep collected plants fresh in the field, put them in sealed plastic bags out of the sun. You'll want to get plants in the press as soon as possible. If you need to keep them overnight, a wet paper towel in the bag will keep them from wilting too much. Alternatively, students can press and protect plants in a phonebook or catalog until they get back to the classroom.

3. Make field notes. If students are planning to create an herbaria or field guide, they'll need to take notes on their subjects. Each journal or field notebook entry should include such information as date, location, environment (e.g., amount of sun), type of growth, (herb, vine, and so on), description of seeds and/or fruits, and collector's name. They might also want to include information that may not be apparent once the plant is dried, such as original color or aroma. (Your young scientists might also make sketches and take photographs of plants in their habitats.)

Pressing Concerns

Simply put, a plant press sandwiches plant parts between layers of absorbant material so they will dry quickly. (This better preserves specimens and color.) Although you can press plants in old phone books or catalogs, a setup that enables air movement speeds up the drying process. Here are some tips on creating your own botanical presses.

1. Place the plants. The interior of your plant press will consist of alternating layers of plants arranged on absorbent material (newspaper and/or blotter paper) and corrugated cardboard. The cardboard enables air circulation so the plants dry more quickly. Students should carefully lay each specimen in between a folded sheet or two of newspaper (or blotter paper, sandwiched in between newspaper). You can lay numerous flowers or plants of the same thickness on the same piece of paper, as long as they don't touch. Try to arrange flowers and other plant parts in a natural way, so their parts will be visible when pressed.

2. Make the sandwich. In between each plant/paper layer, insert a piece of corrugated cardboard. Finally, place wooden boards on either side of your layered pile. Next, you'll need to bind or weight the stack to create pressure that will help the plants dry. You can tighten straps or belts around it or simply put something heavy on the stack. Some presses have screws and nuts in each corner that can be tightened to create pressure. Leave your press in a warm, ventilated location.

3. Check your specimens. Although many plants will dry adequately in ten days to two weeks, some may take longer. If you find they are still moist when you check them, and you have them between more than one newspaper layer, you can change just the outer layer. (The delicate plants, when moist, will likely stick to the piece they're touching.)

Displaying Plant Collections

1. Plan the layout. Before students mount their pressed collections, consider your end goal. If they're creating classic herbaria pages, students should give each plant its own sheet of paper. If they're creating field guides, they may organize pages by plant families and/or characteristics, such as color.

2. Identify your finds. Unless your pressed plants are solely intended for an art project, you'll want to have students identify what they've gathered using online or printed field guides. They may have to extend their initial observations to find specific characteristics listed in the field guide keys. (For instance, Does the plant have opposite or alternate leaves?)

3. Mount them. Have students use a thinned Elmer's white glue to attach plant parts to heavy paper. If a flower, petal, or leaf seems breakable, put the glue on the paper and let it sit until it dries a bit. Next, pick up the flower with a damp fingertip and press it gently onto the glue. Students may want to cover their herbarium or field guide pages with clear contact paper or slip them into clear sleeves before putting them into a binder. Consider diplaying individual pages or collections in a school lobby or at a parents' night, or using them for self- or student-guided tours of the schoolyard, garden, or neighborhood.