Berm

[HRLand]

I have to plant some arbs in a berm due to excessive water. What do you recommend for backfilling, topsoil or plain old dirt?

[Lanelle]

What does your 'plain dirt' look like? In general, I'd recommend mixing topsoil or compost with your plain dirt and using that for the backfill.

[jwholden]

Yeah, what Lanelle said.

If you are going to ammend the soil it's better to go all or nothing.

If you decide to ammend the soil, bring the tiller and mix your new soil with what's already there. If you do not take this step your arbs roots will not move out to the native soil beyond what you brought in. They will do ok in the short term (at least until the warrantee is over) but will have a small weak root system and a less vigoruous tree as time passes.

If you decide not to ammend the soil, don't. Mix a little compost or manure (less than 10%) with whats already there and use that as your backfill. By not overammending the soil close to the ball you have given the roots incentive to grow and spread in search of more nutrients.

Final note, when you say 'excessive' water do you mean standing water that will wick up the berm and cut off the oxygen supply to the roots or an area that gets a bit damp in the Spring and Fall?