"Pat" wrote in message

My question is this: If, as I understand it, the pond needs oxygen
in the water to keep from stagnating and to support fish, and if certain
plants are generally used for this purpose

Not generally in a man made small pond. We use waterfalls, airstones and
such.

and if one needs a liner how are the plants to take root?

Baskets lined with weed fabric holding soil, the plant, & rocks on top to
keep the fish from rooting out the soil while looking for worms.

Obviously they can't get any nourishment from the pond liner

Most pond plants get their nourishment from the water. Many don't need
pots, they just float. Grasses, like hornwort & anacharis will adhere to
folds in the liner all by themselves.

I am trying to plan my first pond.

It would help us if you would explain what your plans are, advice differs
for a koi pond, a goldfish pond, or a water garden with just small fish to
eat mosquitos, etc. Size? Location? Power sources.... Depth? ~ jan
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Zone 7a, SE Washington State
Ponds: www.jjspond.us