Water drainage through hardpan

We planted a fan palm last spring and had to pull it out last month because it wasn't healthy. When I pulled it out, I was surprised to see that there was a puddle of water in the hole - the tree had basically been sitting in a pool of water because of poor drainage.

We had a Crape Myrtle in this same spot and it was very healthy for around 15 years. We also have several Queen Anne palms planted close by (in the same type of soil profile) and they have been doing well for years.


We are getting ready to plant a new fan palm in the same hole and I want to avoid the same issues. The hole is 2 feet deep, but at the bottom of the hole there is clay hardpan. I tried drilling several holes through the hardpan (using a 24" bit that is about an inch wide), but I was never able to clear the hardpan.

What is the best way to proceed to ensure that we have sufficient drainage before planting the our new palm?

 

I have a similar problem at my house except is saprolite. Any hole dug in it essentially becomes a pot in the ground with no drainage. The easy way is to mound so there is enough soil above the impermeable layer for the plant to thrive.

My yard is hilly so I often get out the excavator (track-hoe) and dig a larger than usual hole. From the hole I dig a drainage trench downhill so the bottom of the hole can drain. Then I fill in the excavation with amended soil that can drain. Basically you have to give the water somewhere to go. In your case maybe drill deeper drainage holes and fill them with vermiculite?