Are you thinking of putting the lilacs outside the tree branches or under the trees? How much space do you have to work with? Can you post a photo?

In general, lilacs like sun. You may get leaves but not flowers if you plant them in the shade. Also, it's hard to grow anything under maples. Their roots are really close to the surface so it's not only shady but also dry under them. Since your arborvitae are doing okay, though, maybe you have unique conditions.

The only thing I can get to grow under my maple is ajuga. I'll be interested to hear whether and what shrubs other people grow under or near maples.

I can't speak for anyone else's experience with maples and lilacs coexisting. My house is hidden behind a lilac hedge that was originally planted in 1900. At some point way back when a few maple volunteers appeared in the hedge and are such gorgeous trees my arborist wouldn't dream of removing them. They don't bother the lilacs as they've been carefully limbed so as not to block the sun.

Keeping the lilacs in shade would be the only problem; blooms would be sparse - if that can be addressed, lilacs would be a pretty effective screen when in leaf and reaching some size. Bare in the winter, of course.

Maples cast deep shade and their shallow roots dry out the soil. Lilacs would never grow under maples. I suggest planting native shrubs that prefer dry shade: the native viburnums withe the maple-shaped leaves. They flower, have red berries and great red fall color. Another suggestion would be gray dogwoood.

Despite conventional wisdom saying it can't be done - in close proximity to massive boulevard maples, I've got hosta, bleeding heart, yews, ninebarks, actaea pachypoda alba, Northern Lights azaleas, and a few Stella d'Oro daylilies which, in truth, produce only light bloom.

Maybe the biggest problem people have with maples is in wanting to closely ring the tree with plants. I don't do tree rings. I also don't follow an aggressive watering program much beyond normal rainfall - so I'm not inviting roots to surface all over the place.

But, like I said, I can't argue with other's experience. Lilacs are very common here in MN and quite inexpensive (especially at the big boxes). Maybe the OP could purchase one or two and conduct an experiment in his/her own yard and conditions.

Thanks for everyone's reply. I looked the area over again. It only has one maple (near the street), the rest of the trees are very bare pine trees. The pines are bare at least 6-8 ft.up the trunk. So there's alot of area that the lilacs could fill in. I don't want to kill my pine trees by planting lilacs too close to them. Though I do have an old lilac next to some pine tres in my back yard that continues to bloom. I would move the arbortivaes in front of them just for a second hedge. As far as the lilacs blooming I don't really care, I just want to block out the neighbors and they're junk. What ever it takes to get a peacefull garden.

Just be careful to buy a lilac that will be as tall as you want it to grow. A friend put in a couple of new lilacs and when I looked at the tags, I commented that she had chose one of the new dwarf varieties. She was upset because that had not been her intention.

If you don't care about blooms, I'd go with the native viburnum suggestion (or azaleas or rhododendrons, but they're kind of slow growing). Viburnums are gorgeous and the right varieties are better suited to shade than lilacs.

Your maple garden sounds amazing, duluthib. The problem for me is that my yard is so small, the maple's "ring" pretty much is the whole space. I was exaggerating a bit. I've got Japanese fern and beautiful epimediums under there along with the ajuga. No shrubs though.

Ok Here's a picture. There's a lot of bare space under the trees so shrubs would get enough light. I would really like to have a private garden area so I need ideas for planting in layers. I'd like to move the arborvitae that are currently planted along the fence line forward 5 feet and put a row of lilac in their place. Will the lilacs do ok in front of the arborvitae? The arbors are great but, they grow too slow for me to get the privacy that I want. Any suggestions for laying? I'm also thinking of mixing in some dogwoods.

It's too shady for lilacs in that spot to grow at all. Dogwoods will do fine as will the viburnums.

When you said you would move the arborvitae forward 5 feet and put a row of lilac in their place you should plan more space if you do try lilacs most full size lilacs need more than 5'.
My neighbors have lilac in partial shade it gets late afternoon sun. It does bloom a bit, but it is so thin that it would not be a privacy screen.

You should check out this site from the U of MN. You put in your parameters and it tells you what plants, shrubs, trees will work there. You can search for size amount of sun etc.

Here is a link that might be useful: SULIS

jazzy, thanks for the picture. That helps a lot. You've got a lovely arrangement there. A couple of thoughts.

First, I think your guests' eyes will be drawn to the arborvitae, which create a natural focal point in this setting, especially in winter. Of course, that may not be important to you since YOU have to live with the neighbors.

Second, IMHO I'd keep the arborvitae where they are. I say this for a few reasons. In the long run, they will be taller than any shrub that you plant. In fact, it will take at least a couple years for any shrubs you plant to get as tall as them. Also, they seem to be doing well and will create a great barrier in a few years. If you move them, you decrease their survival chances. This is particularly true under maples or pines, where they will have to compete anew for water and nutrients.

Again, just my two cents, but I think a privacy fence or a lattice barrier, possibly with fast-growing vines, would block the view well. A lattice is cheaper and allows more light through, but a fence provides more privacy.

At any rate, let us know what you decide and how it turns out. Seems like a space with great potential for a shade garden.