September is an opportune month for gardeners to begin collecting seeds, allowing them to create a personal seed library for future planting seasons. As plants reach maturity and their pods, capsules, and seedheads dry out, gardeners can gather seeds at no cost while preserving favourite varieties and contributing to biodiversity in their gardens.

When choosing seeds, it is advised to select those from healthy, vigorous plants and to wait until they are fully ripe. Common candidates for seed collection include dry seedheads from poppies, nigella, calendula, scabious, and sweet peas. In addition, cosmos and zinnias tend to be ready for harvesting as their seedheads dry, while beans and peas can remain on the plant until their seed pods become dry and papery. Experts recommend leaving some seedheads, such as teasels, sunflowers, and grasses, untouched throughout autumn and winter to provide food and shelter for birds and insects.

It is important to note that seeds collected from named hybrid plants may not produce offspring identical to the parent, as these seedlings can exhibit different traits. While this variability can be interesting, gardeners should not expect exact copies when growing from hybrid seeds.

Seed harvesting should be done on dry days, following at least a couple of rain-free days, and after any dew has evaporated. The transition of pods or capsules from green to brown or black typically indicates readiness for collection. Whole seedheads are best cut and placed into paper bags before they disperse their seeds. After collection, the material should be left in a warm, dry, and airy location for several days to complete drying. Once fully dry, pods can be gently opened or shaken to extract seeds, with any chaff or debris removed. Using plastic bags is discouraged because they can retain moisture, promoting mould growth.

For storage, thoroughly dried seeds should be placed into small paper envelopes, clearly labelled with the plant name, variety if known, collection date, and optionally additional details such as the parent plant’s location or flower colour. These envelopes can then be stored in an airtight container along with a silica gel sachet to maintain dryness. Cool, dark conditions are recommended, with refrigeration around 5°C being optimal for many dry-stored seeds. Organization methods include arranging envelopes alphabetically, by sowing month, or by plant type. Gardeners should periodically inspect stored seeds and discard any showing signs of dampness, mould, or insect damage.

Seed viability varies by species; some seeds lose the ability to germinate quickly and are best sown fresh, while others can remain viable for several years if stored properly. For instance, cosmos seeds may remain usable for about three years, whereas zinnia seeds are most effective when planted within two years. Maintaining a homemade seed library not only preserves plants for the future but also serves as a living record of the garden’s history.

Additional resources, such as instructional videos on seed harvesting and storage, are available for gardeners seeking practical guidance. One such example is episode 20 of the "Step-by-Step Gardening" series, filmed at Blue Diamond’s Bridgemere Show Gardens and accessible through the YouTube channel @daviddomoney.