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The thread "List of Florida Arboretums and Botanical Gardens" in
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If you take the by-pass around Jacksonville to the west there is a good nursery at exit 23, New Kings Road. The place is called Gore's Nursery and it is only a few thousand feet (to the west) off 95. Good selection and prices.
EFG Orchids, they carry other plants also, is right off I-4 between 95 and Orlando.
Apopka is home to countless growers and many are open to the public.
You will be driving through NC, don't miss the Plant Delights nursery and their Juniper Level Botanical gardens. A commercial nursery nearby is called Big Bloomers and it it worth a side trip for the variety and prices. The place is HUGE. Many, many greenhouses.
Also right off 95 is the Costal Georgia Botanical Gardens just south of Savannah.
Although about an hour from 95, there are gardens large and small in Charleston, SC and April is an awesome time to visit. Walking the historic district and visiting the private gardens is amazing.