This is the major seed collecting time in the gardening calendar. Some seeds have had to be collected earlier, but most are only ripening now, in the fall. Ideally, they should be left on the plant as long as possible to give them time to completely ripen. There is a fine line, however, between making sure seeds are ripe and waiting so long that the seeds are blown off in the wind. Some of the ones I collect are for use the next year (for instance, seeds of heritage tomatoes or of annual flowers, like yellow cosmos). Others I gather to send in for the seed exchanges I take part in.
|Bottle gentian seeds|
On the whole, the bigger the seed, the easier it is to collect. Some like peonies or canna lilies have huge seeds that are very easy to gather. Apparently, one common name of canna lily, Indian shot, refers to the fact that they were used as ammunition in musket rifles. That tells you how hard they are.
For many, if not for most, of the seeds I gather, I simply take the pod of husk, turn it upside down and shake it. This works very well for the various dianthus. The pods are all facing up and are open at the top when the seeds are ripe. You just break or bend down the stem, shake the pod, and the ripe seeds fall off. Some husks, for instance Nigella damascena (love-in-a-mist), are not open even if the seeds are ripe. However, you simply break the husk, and the seeds fall out.
|Collecting Dianthus seeds|
Some seed heads, like those of lilies and iris, you simply opened and you find the seeds all carefully lined up in the pod, ready to be gathered. You have to wait till the pod is dry to make sure the seeds are ripe. In the photo below, the lily seed pod is not yet ripe.
|Lily seed pod|
If you are afraid the wind will blow your seeds away before you have time to gather them, you can simply bag the seed heads and later on retrieve the seeds from the bag. An advantage of this technique is that once they have fallen in the bag, they are most likely ripe.
For most of the daisy-like plants, such as the purple coneflower (Echinacea purpurea) or the various rudbeckias, the seeds are all clustered in the centre of the bloom, and you simply pull them out. You have to make sure you do not end up with only fluff, but also with ripe seeds. That is where winnowing is useful. You put your material in a pan and shake it in a light wind. The chaff is blown away in the wind, and you are left with the seeds which are heavier.
You can also use strainers/sieves of different sizes to sort the seeds from the plant debris. However, I have not much luck with that technique, and besides, I found it difficult to find sieves with different sizes of meshing.
Some plants, for instance lettuce, I let go to seed and collect as much as I need, but most of the seeds are left to scatter. In the spring, the seeds that the wind scattered are always the first to produce strong lettuce plants. I just move these small volunteers where I want them.
|The fuzzy white seeds of lettuce|
Some seeds come in a fruit or berry. This is the case for instance of pokeweed (Phytolacca americana). You can clean them like tomato seed, that is to say you let them ferment for a while, and the pulps comes off the seeds. For pokeweed, since the seeds are bigger and harder than tomato seeds, you can simply squash the berry between sheets of newsprint, let the pulp dry and then collect the seeds.
With some plants you simply cannot get the seeds. I have lots of thyme varieties, some that even self-seed, which means they do produce viable seeds, but I have never been able to gather them (thyme would probably be one plant where the paper bag over the seed head technique might come in handy).
It is interesting to note that, even if you collect seeds every year, from year to year your seed crop will vary. Some years you will miss some, other years some plants won't produce seed. So you end up with a different set of seeds most years. For me 2013 was a good year. I was able to gather a greater variety of seeds than usual.