Have you tried stratifying the seeds by putting them into a fridge for a few months prior to planting them?

Hi, do you have a VERY large garden, or are you going to plant them in the wild ?, they're not called 'GIANT'red woods for nothing, Derek.

Hi Pelican have a look at this link http://www.monumentaltrees.com/en/trees/giantsequoia/growing_your_own/

It does suggest that trees have to be quite mature before they produce viable seed but the likelihood of growing trees from seed is hardly recommended. If you are successful after stratifying the seeds for 2 days to 2 weeks they need to be pressed on to compost and kept over a radiator and also should be covered using a plastic bag to keep them moist. Success will be yours when you see a rhubard coloured seedling appear. I think you need to read the info on the link. It might id why you have been unsuccessful. As Derekm says they are huge and not at all suitable for most gardens.