The most common suggestion I have found has been to plant in a mix of peat moss with aged pine bark fines (sometimes sold as soil conditioner) and native soil. The exact proportions of these 3 ingredients does vary though.

If your soil is very alkaline, maybe you want to opt for a raised bed instead. Fill it up with peat moss and aged bark as Ike suggests, minus the native soil. Over time it will be much easier to amend the soil if ph raises.

Depends what you mean by very alkaline, but I wouldn't bother wasting your money and time. Keeping the pH low will be like trying to keep a bucket filled that has a hole in the bottom. If your water supply is also alkaline it will be even harder.

A raised bed is good, or even large planters. Collecting rainwater would be your best bet for water supply.