Kay wrote:
Then I'd plant them straight away, with just a fine scattering of soil
on top ...
- SNIP -
If nothing happened in the first 3 weeks ...

Even seeds of most rose species that have passed through the gut of
birds need a period of chilling before they will germinate, so washing
the seed will not make much difference in this respect. However,
cleaning the seed to remove hairs and remnants of the husk will reduce
the risks to the embryo that are presented by moulds and bacteria,
which gain a foothold on decaying remnants. Rose seeds are best
cleaned and sown immediately after harvesting and then covered with a
5mm layer of fine grit or coarse sand. They should be placed in a
cold frame or outside where they will be exposed to several months of
cold or even frost. In spring, they can be brought into the warmth
where they will germinate within a week or two. Watch out for mice,
they are very fond of rose 'nutlets' and will devastate pots or trays
of seed in no time at all.

This process can be accelerated with the use of a domestic fridge set
to maximum. The cleaned seeds are mixed with barely moist sand or
grit, sealed in a plastic bag and subjected to approximately 0 to 3C
for 6 weeks. The seeds are then sown just below the surface of
sterilised compost and maintained at 21 - 23C. Germination usually
occurs within 7 - 10 days. However, very poor winter light intensity
in this country means that any resultant seedlings will be weak and
etiolated so there's little or no advantage for the average gardener.
Even growing under lights results in atypical soft growth.

Most species roses will produce their first flowers in the second year
from sowing, but hybrids from 'garden roses' can produce the first
flower in as little as 3 months from seed. However, the chances of
such plants going on to produce worthwhile flowers on a strong healthy
plant are exceptionally remote. Even when parents are carefully
selected and cross pollinated, it's a lottery and more often than not,
the progeny of a 'good' pairing will result in duds. There's an
entire industry devoted to this and millions of rose seedlings are
destroyed annually because the vast majority are just not worth
growing on. That said, it's quite fun raising roses from seed
collected in the garden. They will show considerable variation and
none will be the same as the parent plant. You never know what might
crop up. It will probably be rubbish, but it will be your rubbish and
unique.