See The Garden, RHS February 2013, pp 58-62 for guidance on seed collection techniques; see also RHS, The Garden, September 2019, pp. 49-51.
Seeds to save: annually flowering plants such as cosmos, nicotiana, nigella or cleome.
Semi-hardy seeds to save: calendula.
Collect at the moment of dispersal. You can tie a bag over the seedhead before it has ripened.
- gather on dry days. If it has rained, wait a few days before collecting.
- don’t forget to write the name of the plant on the storage bag, along the with the date you collected the seed.
- don’t store seeds in plastic bags; use paper envelopes instead.
This is when you scratch the surface of the seed coat. The easiest way to do this is to line the inside of a glass jar with a piece of rough sandpaper – add the seeds and shake a bit.
Some seeds can be soaked up to 6 hours before planting – such as narsturtium and peas.
This is when seeds are combined with moist potting compost and subjected to a period of cold or warm to simulate environmental conditions needed for germination.