Tricks and tips:
- If you prefer to store your seeds in small, airtight jars rather than envelopes, include a desiccant to keep them dry: silica gel packets from pill bottles or calcium chloride (sold in DIY stores for dehumidifiers) willserve the purpose.
- Never store seeds in polyethylene baggies, as they trap moisture and cause seeds to rot.
- Never store seeds in the freezer; going from room temperature to below 0°C in a short period will kill the seed embryo.
Only collect seeds from healthy, vigorous plants. The best time to harvest is mid-afternoon on a sunny day, but never after it’s rained or when it’s damp with dew (to avoid mould). Most flowering plants ripen their seeds successively over several weeks, so be sure to harvest mature ones (those that are brown or black). Capsules usually start to split when seeds are ripe.
Arm yourself with some brown paper sandwich bags, a clean pair of secateurs and a black marker. Cut off mature seed heads and place upside down in the paper bag; label and date the bag, and fold it shut at the top.
Once you’ve finished harvesting, bring the brown bags indoors, open the tops (for air circulation) and place in a dry, breezy room for several days. Shake the bags occasionally to encourage seed drop.
After the seeds have dried and dropped, remove any sticks, stems or chaff. Some gardeners like to spread the seeds on newspaper to separate them out; others prefer to use fine-meshed kitchen strainers.
Next, store the seeds in small manila envelopes (remember to write the plant name and date the seeds were harvested on each package). Place them in a cool, dry area, such as a cellar or refrigerator, over the winter.