Zagreb for me does not bloom all summer, more like 6 weeks or so. You might want to think about adding some annuals to keep the interest going into fall. In most of my beds I try to grow about 30% annuals, higher if a bed is new and the other plants have yet to reach a good size.

Yoshino Cherry is one of my favorite cherries, they are particularly graceful and their bark contrasts nicely with the whitish pink flowers.

Can't say I know anything about ipheion, unless it has a common name the rings a bell. I grow a number of semi invasive plants. Most of them aren't a big problem as long as you're willing to put in the extra work to keep then inbounds.

You might want to let everyone know what kind of growing conditions your bed has - full sun or not, wet or dry, morning sun and afternoon shade, etc. Then would get more useful answers to your questions.

Ipheion is a bad idea. If you do a search on the Gardenweb forums, you'll find many horror stories about this bulb taking over the neighborhood. Also, it blooms early in the spring, and the bloom time wouldn't coincide with the coreopsis.

From the bulb forum:

RE: I have thousands of annoying little bulbs

Posted by: Jenn 9 (My Page) on Sun, Apr 17, 05 at 13:34
Yep, they sound like Ipheion. I planted a few here and there several years ago and now I have THOUSANDS in those areas and spreading to other areas due to the seeds that scatter after they bloom. Seriously, this will be my biggest gardening mistake EVER. One evening I spent hours digging them out of a small (2'x 2') area and found HUNDREDS of them. Guess what -- they are back, in the same area! They are all over the front yard now.... coming up at the base of plants that I will have to move to get the bulbs out. I feel sick about the amount of time it will take to get them out.
The bulbs are very small -- the largest about the size of a garlic clove. In fact, the leaves smell like garlic or onion. Cute little plant but I wouldn't plant it again unless I lived on 100 acres and wanted to cover the back 40 with a little grassy bulb that could take care of itself for years to come without any attention from me.

Jen

RE: I have thousands of annoying little bulbs

Posted by: MarcR z 8 OR (My Page) on Sat, Apr 30, 05 at 4:41
Please don't spread invasive plants arround!!!! You can't keep them in your own yard, and your neighbors don't want them.
Roundup is a Glyphosate product which is not likely to be effective. There is a product called Crossbow which is a combination of 24D and butoxyethyl ester. That should be more effective but if the weed is as noxious as you have led us to believe, the only way to get rid of it is to tarp and use a fumigant. You will need to hire a licensed pest control operator to apply Vapam or Methyl Bromide which will kill all animal and vegetable life in the soil.
The soil will be safe to plant in after about 6 weeks. You will probably do well to buy ladybugs and beneficial nematodes and work well rotted manure into the soil after fumigating to restore the beneficial bacteria needed for healthy plant growth.

Thanks, folks. I did catch the postings about ipheion in the other forum and decided against it. I decided on balloon flowers, instead. I ordered the seeds and they should be here in a week.

The bed I'm working on is in full sun, from about 10:00 a.m. to sunset so it's in the northwest corner of my property. Pretty good drainage and tons of earthworms.

Now, if only it would stop raining this week!

You want it to STOP raining? I've been doing the rain dance for weeks! ;-)