Most books state that seed should be collected when it is ripe, but this is not very helpful. In ideal circumstances a seed head is ripe when the capsule turns brown, starts to split open (dehiscence) and releases the black or dark brown seeds. However, garden conditions are frequently far from ideal and a wet summer can result in the seed heads rotting away before any seed can be gathered.
In dry weather seed heads should be gathered as soon as they start to split but in wet conditions it would be prudent to gather swollen seed heads just as they change from green to a brown colour. The collected seed heads will continue to mature if left in a cool, dry room away from strong sunlight. Mature seed should fall out of the fruit capsule quite readily, but sometimes dry capsules do need to be broken open to release the seed. This process can produce dust, hairs and bristle fragments which may cause skin and eye irritation.
At this point there will be a mixture of fat mature seeds, small non-viable seeds and chaff, which will harbour fungal spores. Because of this cleaning is essential before storing the dry seed. There are several ways of doing this.
Method A: Using sieves
Metal flour sieves and tea strainers have a variety of mesh sizes, and can be used to remove fine dust or large seeds. Plastic sieves are less useful as they can carry an electrostatic charge.
Method B: Tapping and rolling
Round seed will roll, so gently tapping a slightly inclined glazed dish can separate viable seed from bristle fragments, hairs and other chaff
Method C: Using electrostatic attraction
Plastic containers produce an electrostatic effect when rubbed. This will attract and hold small particles of chaff whilst the larger viable seed can be poured out.
The clean, dry seed should be kept in sealed glassine packets or small paper (not plastic) envelopes, labelled with the plant name, source and date. If not for immediate use, the seed can be stored for some time in an airtight plastic container placed in a fridge.
Fresh seed germinates better than old seed but, as with other genera, the ‘shelf-life’ of different species can vary quite considerably. For example, seed of Meconopsis punicea is best sown immediately, as seeds sown in spring may not germinate until the following year. Even immature ‘green’ seeds of this species have been known to germinate within a couple of months. Seed of others, such as Meconopsis ‘Lingholm’ may remain viable for more than 5 years, but with a reduced percentage germination.