If the plants you have survived , then those are the hardy ones and you wont have to worry about them . As for any tropicals , treat them like house plants , just keep the dirt wet . Rick

What plants do you want to overwinter? Depends on what plants for the best advise to overwinter.

Generally, tropical marginals can be brought indoors and left inside their pots submerged inside a a second waterproof container (a bucket). Situate them in the sunniest window you can find and keep the bucket filled with fresh water and occasionally add weak liquid fertilizer. You can prune or divide if you want to trim them up for winter. Or bring in a few nice pieces and discard the rest.

Large planters filled with water can be daunting.

Some plants lend themselves to planting in soil like elephant ears and placed in sunny windowsills. Water and fertilize when needed.

Plants like water hyacinth and water lettuce, best to throw those out IMO and start with a couple of new plants each year as they don't overwinter well inside and they are cheap to replace.

Tropical water lily you can pull the whole pot and put in a plastic bag and put in a cold, but frost free location (like a basement). The idea is not to actively grow them all winter but to keep them alive, semi-dormant. Some folks keep them actively growing in an aquarium. Some had said they have no luck at all with overwintering tropical waterlilies and replace them.

Unless the plant is rare or expensive you may find it less hassle to just buy new every season.

Sometimes if a plant is on the edge of it's zone you can leave it outside provided it is well protected. Like a zone 8 plant in zone 7. But, a zone 11 plant will bite the dust in all but the most tropical locations, without going to extraordinary measures (heating coils and greenhouses).

To comettose:

This may be somewhat off this topic, but when you have to replace items which are tropical and must be kept in a protected place throughout the winter, can they be kept in a garage which is semi-warm? Also, what would you estimate that you spend on aquatic plants each year? I am a newbie and look forward to this new venture and also need to buy the products essential for keeping the new pond healthy.

Thanks.