Another thing you might want to try...It's a tip I learned from a champion rose grower here in Minneapolis. He mixes Alfalfa meal (buys it in 40lb bags at the local seed Co-op) around his roses. Seems the Alfalfa contains a hormone that allows plants to take-in nutrients from other fertilizer sources much, much better. I grow some roses in amongst my other perennials and bulbs and broadcast the Alfalfa meal all over my gardens (like you'd do with the bone meal) and let the rain/sprinkler system create a "green tea" for the plants. My bulbs are fantastic...my Casablanca Lillies grow to 6'6" tall. I swear by this stuff and stock-up on a supply every spring.
When I'm converting a sodded area to a flower bed, I need to amend the soil because I have a lot of clay. Here's when I buy the Alfalfa in pressed cube form (like horses eat). I take a large rubbish container (55 gal), pour in the cubes and fill the container w/ water and let the cubes hydrate. Then I roto-till the cubes into the soil along with smooth pea gravel...yes, pea gravel (about 3/16"-1/4" in dia). This is another tip to help loosen the soil and allow water to pass through. I learned it from a gardner in England. Think of putting your hand into a bowl of hard peas or beans and how easy it is to push them around. That's the same benefit of the smooth pea gravel in a dense soil...it helps to keep it loose. Most people advise digging-in peat moss. I've always found that it makes the soil rather gummy & dense after a couple of years. My pea gravel just keeps doing its job, year after year! It's important to get the smoothest gravel as possible though. There are many choices of "rocks" available from rock/sand suppliers, but if the gravel surface has sharp edges, it doesn't work as well. I tried some small lava rock one year and its rough surface only bound things together. So that didn't work!
In place of peat moss, I have a free (City provided)source of composted leaves/twigs. I dig this in as well. Also after you've dug the Alfalfa cubes in, I let everything sit for about a week and then do my plantings. You'll find that the Alfalfa will kind of ferment in the warm soil and it will have a bit of an odor...the flies and bees will also be attracted to it, but the smell will soon go away.
Finally, after all the plants have started to grow, don't forget to fertilize w/ whatever you normally use. The Alfalfa's job is to improve the plant's ability to absorb the fertilizer...thus the plants grow bigger and stronger.