Highly, highly unlikely that adding a mound of dirt will keep apple tree roots dry enough to survive, wireman. There are plants that have adapted to perpetually wet roots, but stone and pome fruits are not one of them. If you're wanting to plant an apple tree, find a well draining area of your yard, much away from the marsh. Otherwise I fear you're wasting your time and money.

Patty S.

There is no question that if you build up only a 1ft high raised bed in your marsh that the roots of the plants in the raised bed will stay wet. Maybe a 4-6 foot high raised bed would work, but sounds impractical.

And if the rest of your yard is low-lying and if you dig down in your yard where you might otherwise plant, and find water, I am afraid that it will not work there either. Roots of apples won't tolerate that kind of soggyness.

I think you can plant an apple tree in the marsh. It depends a lot on soil prep and the rootstock. I have seen wild apple trees growing in very wet places. I think many of the commercial rootstocks are not very tough or adaptable. They are bred to have small statures and early age bearing.
I think if you collected seeds from wild trees growing in soggy soil, you'd have an excellent rootstock for your purposes.
Also, I would build up a large mound to plant on, at least 8 feet in diameter, maybe 2 foot or more above grade at the center.
It's not impossible, apples are incredibly diverse and adaptable. I think they can grow wherever multiflora rose grows.

No first hand experience. But I think a 2ft or taller mound would work.

This doesn't exactly answer your question, but I've heard from another poster here that hawthorn trees can handle marshy conditions and are graft compatible with some pear varieties including Old Home, or was it Farmindale?

You could grow whatever variety of pears you choose using an interstem.

I have planted in marshy areas with standing water much of the year. You just need to mound up the dirt very high. I created mounds 3' above the standing water.

There are areas along the Mississippi river where orchards have been traditionally grown where the water table never drops below about 24". But it generally doesn't rise much above that either.

My trees (fruits of all kinds) are in mounds with some in their eighth year. Now I don't know if they'll survive to 20 or even 50 years I do think its worth trying.
But do find the driest not wettest area to start the orchard.

this is something i have wondered about often. I think american chestnut has it more or less right. I too have noticed many old feral apple trees growing in wet areas...with a stable water level. They seem to do just fine with a 1-2' lift of well drained soil.
There was one nice old tree growing on an even thinner rise on a nieghbor 's property. Blew over 2 seasons ago and the void where the roots pulled up have pretty much become a vernal pool.

I had hoped it would send up suckers, as I was interested in propagating it as a potentially damp tolerant rootstock, but no such luck.

Here in the northeast beavers often convert reasonably well drained soil into marshland. I have seen entire seedling rootstocked, abandoned apple orchards surviving is what is muck most of the year, most seasons.

It is also common to see healthy blueberries in marshes on individual hillocks rising well above the water table. I don't know how these hillocks were originally formed.

Witnessing these blueberries taught me about the power of mounding soil in wet sites back in the '70's. I was a gorrilla grower of herb back then and this knowledge was money.

I live on a small creek. The canal is about 20 feet wide and 12 feet deep, fresh water and flows into the Gulf far from my home. The water table is about 1.5 feet down at about 15 feet from the water's edge.
I've planted 2 pears(about 3 feet apart) on a mound about 8 feet wide and about 2 feet high. Also planted a trio of apples about 3 feet apart in a triangle formation also mounded at about 2 feet high. Both mounds are about 15 feet from the waters edge. During the past year both mounds have settled to about 1 foot high and have to have dirt respread over the top about once a year.The creek overflows its bank about 5 times a year and for a period of maybe a few hours each time. All plantings are in their second year and doing well.
I know this is not your circumstance but just letting you know.