Pressing and drying

Pressing and drying plant material

When dry, plant material is brittle and difficult to manipulate. In order to finish up with a collection of useful herbarium specimens, you will need to be careful about arranging the fresh plant material in the drying paper and plant press. Once the drying process is finished, any mistakes are difficult to reverse.

  • In order to avoid mix-ups, a small temporary label indicating what the sample is, where it was collected from, or to which set of collecting notes it belongs, should be attached to each specimen before placing it in the plant press.
  • Place the fresh specimen on an open fold of newspaper (one thickness is sufficient). Take care to arrange the specimen so all features can be seen.
  • Place the single fold of newspaper containing the specimen between several more layers of drying paper (newspaper) or absorbent material. 
  • Place a corrugated cardboard ventilator sheet (from a cardboard box) between the layers of drying paper to ensure an adequate flow of air within the press (Figure 1, overleaf). Several specimens in such an arrangement can be stacked on top of one an another to form the press.
  • Place the stack on top of a piece of 5-ply (or other wood) of sufficient size, and place another piece of 5-ply on the top.
  • A weight (heavy books, etc.) should then be placed on top of the stack so that a “reasonable” pressure is being applied to the plant material.
  • Another good option is to “squeeze” the stack using ratchet tie-downs.
  • The drying process occurs most effectively in an area of warm circulating air. Good results can be obtained using a hot water cupboard, a radiator heater, or even the sun. However, it is imperative to change the drying papers regularly (i.e. change the papers twice a day for the first three days, then at least once a day until all the moisture has been removed from the specimens. Most plant material will dry within 1–3 weeks. However, drying times will vary greatly, depending on specimen bulk, resins, succulence etc. Use of a microwave oven is not recommended as material tends to cook or catch fire. Seed viability may also be destroyed.
  • A useful test to use to ascertain when specimens are properly dry is to press the plant material to your lips. If it feels cold to the touch, or is limp and flexible, it will not be dry.

This page last updated on 23 Sep 2012