I see gardens that have items that are 'out of date':  like previous zodiacs that you cannot purchase anymore, or halloween/Christmas type items.   How does that happen?  If I wanted to puchase previous zodiacs, but they're not offered, how do I do it, please?

You can only plant seasonal flowers for some limited period after they disappear from shoppe. It's guaranteed that they last at least one more week, but it's often longer. Most fairies use self-gifting method to get those "not yet expired" flowers. You can find more about self-gifting in fairyland guide (the top section of this forum) or various fan sites. :)

Can they be stored to use at a later date?  I've seen some zodiacs in gardens that date back to December...so I'm curious how they do it.

I'll copy the post from the fairyland guide for you:

~ POST 28 ~
~ SELF GIFTING METHOD FOR LIMITED EDITIONS ~

You need 1 FB friend who has FAIRYLAND on their FB account for this link to work
(This may not work for everyone)!

Use this link
http://apps.facebook.com/fbfairy/req.php?z=0&reqtype=GIFT&ts=0&from_uid=X

Replace the X at the end with the FB ID No (back wall No) of one of a Fairyland friend.
Replace GIFT with the numbers corresponding to the one you want from the list below.

Remember these will only work while in season!

5001 Pink Ribbon Plant
5002 Halloween Plant
5003 Poppy
5004 Poinsettia
5005 New Years Flower
5009 Snowman
5010 Christmas Tree
5011 Ice Flower
5012 Loveflower
5013 First Flower of Spring
5014 Earth Flower for Earth Hour
5015 Daffodil
5016 Earth Flower for Earth Day
5017 Shamrock
5020 Gemini
5021 Cancer
5022 Leo
5023 Virgo
5024 Libra
5025 Scorpio
5026 Sagittarius
5027 Capricorn
5028 Aquarius
5029 Pisces
5030 Aries
5031 Taurus
5200 Mothers Day Bouquet

Copy & paste the completed link into the address bar at the top of the page.

Just a note:
It's easier just to accept any gift and only change the number of the flower instead making the link from scratch, looking for facebook ID etc. :)

You can keep plants as long as you wish in your garden, but you can't plant new ones after they expire. For example Christmas tree is not available any more, but Shamrock (which is gone from the gifts for couple of months already) still can be planted. :)

If you check, odds are the plants have just been there ever since

I've a friend who still has 2011s loveflower out and I'd bet that aint even a record

They stay at the ready for harvest stage indefinitely.

I have a hard time keeping a plant a week, don't know how they keep them years LOL

Sometimes you will run across a garden with a flowering out of season plant, just means they froze their garden at the time they had it and have recently returned.  When I started three years ago it was just after Easter and hadn't spotted an Easter Bunny.  I found one in October or November in a garden the person had unfrozen :)

But I have seen a few gardens with daffodils that are not ready of harvest, how do people have these.

Daffodils are one of those plants that can still be self-gifted as described above.