Seeds are usually dry within three weeks and ready to prepare for storage. You will want to separate seeds from other plant material. Shake the seeds free gently. Seeds that don’t come free easily are not mature or may be infertile.
Clean the seeds before packing and storing. Most seeds can be cleaned by three methods.
- Sieving. This removes hairs, grains of sand and miscellaneous plant material. Standard kitchen sieves can be used.
- Winnowing. This method removes underdeveloped or infertile seeds, and miscellaneous debris; viable seeds tend to be heavier. Place the seeds in a shallow cardboard box and blow lightly across the surface, removing debris while leaving the seeds.
- Hand-picking. Tip the seed sample onto a sheet of white paper or light-colored card. Carefully separate the good seed from bad with the point of a knife. This can be tedious.
Put the clean, dry seeds into paper envelopes with securely sealed corners. Clearly identify the seeds by writing on the name of the plant, dates and locations where collected, and other useful information. Avoid using water-soluble ink; pencil is more reliable. Stick-on labels may not adhere long-term.
Short-term storage of seeds can be accomplished for most seeds by storing them in paper bags or envelopes (as mentioned above) in a drawer in a warm, dry room. Seal the corners with masking tape to prevent seeds from falling out. Don’t store them in an unheated shed where humid conditions can cause mold growth and the subsequent loss of seeds.
Long-term storage can be accomplished with small, dry orthodox seeds. They are not usually damaged by below-freezing temperatures. The drier and colder the conditions, the longer the storage life. Seeds can be placed in an airtight box with a desiccate such as silica gel which is safe and easy to use. Such storage boxes can be removed from the freezer for several weeks if freezer space is needed temporarily, provided the dry atmosphere inside the box is maintained. Silica gel crystals may get saturated with water and blue indicator crystals may turn pink. Refresh the silica gel by pouring the crystals into a shallow baking pan and bake at 300 degrees Fahrenheit for two to three hours. Baking will reactivate the crystals and they can be returned to the box of seeds and packed back into the freezer. This system of storage is essentially the same as that used at seed banks. Keeping temperatures at 5 to 10 degrees Fahrenheit ensures prolonged viability. Some seeds can live indefinitely in these conditions.
A seed germination test can be done a couple weeks before seeds are to be planted. Sow a sample of seeds on a damp paper towel in a plastic box with a tight-fitting lid. You can set out pinches of different seed in a grid pattern and put the box in a warm environment (64-75 degrees Fahrenheit). If a high proportion of seeds in a cluster germinate within a short time and produce healthy seedlings, consider the seeds to be viable. If seeds do not germinate within two weeks but appear firm and unchanged, they may still be viable. If most seeds in a cluster are moldy after two weeks or disintegrate when squeezed between finger and thumb, they are not viable.
Some seeds with hard coats may need a fragment of the coat removed with a knife before they will germinate.
Collecting and cleaning seeds in fleshy fruits will be covered in a future article.