The following steps are intended to help in the collecting and pressing of herbarium specimens. These guidelines will help in creating useful and long-lasting herbarium specimens.
If you want to prepare your own herbarium samples, here is some of the equipment you will need, and some suppliers.
• Plastic bags
• Tape measure
• Labels/sticky notes
• RHS Colour Chart
• Two pieces of hardboard/plywood measuring approximately 40 x 30cm (16 x 12in)
• Sheets of blotting paper
• Sheets of corrugated card
• Foam sheet
• Bricks/telephone directories/weighty books/straps
• Acid-free paper measuring 42 x 27cm/ A3
• Labels, preferably acid-free
• Neutral-pH PVA adhesive
• Neutral-pH adhesive, gummed linen hanging tape
• Plastic bags
1. Collecting: Select a typical plant and if possible two or three extra flowers to supplement the specimen and for dissection. Ensure the plant is healthy and collect average-sized leaves and flowers typical of the plant, not the biggest. Photograph the plant habit and a close-up. Attach a label with the name and date and location. Avoid collecting material in wet weather.
2. Describing: When collecting, record the following: name of plant, date of collection, collector, site of collection, original source of plant. Note other details that may be lost by pressing: overall size, habit and form, leaf or flower scent. Record colour of the fresh plant using the RHS Colour Chart.
3. Pressing: Remove soil from around the material. Use a press made with a pair of boards of hardboard or plywood cut to the same size as the drying paper. Place some corrugated card on one board, then place two sheets of the blotting paper on top of this. Arrange your plant material on blotting paper retaining the character of the plant. Remove leaves and flowers of congested specimens to reduce the bulk without losing the character of the plant.
4. Pressing: Cover the sample with two further sheets of blotting paper and corrugated card. With both bulky and fleshy specimens, add a sheet of foam between the blotting paper and corrugated card. Any absorbent fabric may be useful in drawing out moisture; place it on top of the plant material, with a thin sheet of paper between the plant material and the fabric to prevent sticking.
5. Pressing: Once all samples have been included, cover with the top board and place bricks or a heavy object on top, applying pressure evenly throughout, or use straps to keep the press tight. Place in a warm place, such as a drying cabinet, airing cupboard or damp-free room above a radiator.
6. Pressing: Inspect the material 24 hours later, replacing the corrugated card and top layer of blotting paper with dry card. This is your last chance to rearrange any material while the plant material is still moist and pliable. Inspect regularly - at least once a week. Depending on the plants being pressed and the drying conditions, a dry specimen will be ready in anything from two to three days to two to three weeks.
7. Mounting: The RHS Herbarium uses acid-free paper, measuring 419 x 276mm (16 12 x 11in). Good-quality A4 paper, preferably acid-free, is sufficient for the needs of a domestic herbarium, but if one day you might like to donate it then consider the advantages of a larger format.
8. Mounting: Attach the specimen to the paper using a combination of neutral-pH PVA adhesive and gummed linen hanging tape. The label should include the plant name and author, plant family, description, location, date, collector and any other relevant details. The label should be placed on the bottom right-hand corner.
9. Storage and conservation: Place the prepared specimen in a sealed plastic bag and freeze for 72 hours. Ideally the temperature should be -32°C (-26°F) although most domestic freezers have a minimum of -18°C (0°F) . Freezing is the only method open to combat pests. The most common pest of the herbarium specimen is the biscuit beetle. Regular freezing (every six months) is recommended, as is regular inspection to check for infestation and damage.