See if you can find them as single stems already. There are some with pretty impressive bark. I'd tend to think you could get away with a 3' tree lawn or even less but remember if you buy a larger tree the soil ball will have to have a wider planting hole and you want to make sure there is space to dig said hole.

It doesn't sound like they do but if your plans include the public street you should probably go over your plans with the public official(s) in charge beforehand. Some communities have all sorts of rules about planting in their streets.

Here is a link that might be useful: Crapemyrtle: A Summer Show Off©

The mature height of the various CM cultivars can vary from 3 feet to 40 feet, so check that out before you buy them and put them in. They look MUCH more graceful if allowed to grow naturally and not topped (pruned annually back to stubs, also known as "crepe murder"). The impressive bark tends to come with age, and the larger ones are usually topped when they are dug as B&B trees. You might do better, and the planting holes would be smaller, if you go for 5, 7 or possibly, 15 gallon pots, as this size plant will more than likely not have been topped. The first 2 size pots would not need really big planting holes, and should grow fast enough to make an solid row in a year or so. The impressive bark will come as they age.

I would allow at least 4 feet from the sidewalk, 5 or 6 might be better - as the trees grow and as they flower, the branches will spread out and hang down. Having these get in the way of the sidewalk users is probably not a good idea. That said, I dodged many plantings that were overhanging the sidewalk when I lived in San Francisco. I also grumbled about many of them!

Since you want them to grow into each other, planting at a distance of 4-8 feet, depending on how many plants you end up with, and the space you can allow, would be adequate. The closer distance will give a tighter "hedge" sooner, and the wider one will allow for good air circulation and let the branches spread out more gracefully. Unless you make sure to get a mildew resistant cultivar, the better air circulation might be important, as some cultivars, usually the older ones, are prone to powdery mildew.

shel, do your research on the varieties. There are several 'lavender' crape myrtles. You will want to select one of the many National Arboretum cultivars or other introductions that provide a good deal of disease resistance and which can be trusted to live up to the description of their mature size. Keeping them under the power lines without constant pruning is imperative...and cultivar selection can do that.

It is also absolutely mandatory that your trees will not block the view of car or truck drivers, or pedestrians. If they do, at any time in their development, they are likely to be removed.

DO contact your city planning office and find out if there are any specifications for planting in such a location. Information gathering on your part NOW will save you some heartache and headache later.

Thank you so much for all of your suggestions and advice!

I am wondering if the Muskogee Crape Myrtle would work there, or if I am out of my mind? I have read it is mildew-resistant, which could be important here. The mature height is supposed to be 15 to 25 feet, so I am assuming with pruning I can keep it to 20 feet in later years?

Perhaps more important is the width--up to 20 feet in the description, but is that controllable with annual pruning (and not "murdering")? I don't have any experience with these trees, so I'm not sure how much I can control the shape--any voices of experience welcome!

Does anyone have suggestions of lavender/purple varieties of crape myrtle that are mildew resistant? My ideal tree would be 10 to 15 feet tall. As stated earlier, I'd like to plant as close to the sidewalk as I can. I'm hoping for a 3-foot tree lawn, possibly with lambs ears as an underplanting.

Thank you for your help!

If you can get, and keep, the crepe myrtle to a single trunk, it won't be as wide as a multi-trunked tree. The flowering branches do extend pretty far out, and can hang down/droop gracefully as the blooms open, possibly as wide as tall, but I haven't measured any big ones that were single trunk. That's why I suggested planting further from the sidewalk, so it doesn't block the walk. You could trim any branches that overhung the walkway back to the trunk, although the CM as a whole might look lop-sided.

I am not sure you WANT to prune a 20 foot tree to keep it lower, unless you have access to a cherry picker, as it's rather hard to be safe that high up and reaching to prune? (if you are an aerialist, line-man, or professional arborist, then never mind) And CM's don't look good pruned shorter, IMO. Look up "crepe murder" on this forum or Google for it, and find photos of each, and you can see the differences in "murdered" treees and trees left to grow naturally. Trimming for shape is one thing, trimming for height is much harder to do and keep the tree looking natural. Try to find a CM cultivar that won't get taller than you want the ultimate height to be, and be aware that it will take some years for it to grow to that height.

While I love lamb's ears, unless you get a non-flowering variety, be aware that it might not be the best for next to a public walkway. The bumble bees LOVE the flowers, and while you do have to work pretty hard to get a bumble bee to sting, it might upset the neighbors and passers-by to hear and see them buzzing happily. Not many people are aware of the differences between bb's and honey bees, and can react badly to any buzzing, bee-like insect.

I have five "Yuma" crape myrtles planted in a row on my property line. I didn't have any problems last year with aphids or mildew, but mine are still pretty small. "Yuma" is supposed to max out around 18ft.

I have 32 varieties of CMs, but they're all red.

What caught my eye here was your desire for a 20' tree. I second the idea of not trying to contain a tree that naturally wants to be bigger or drape-ier. Buy one that already has the features you'd like. The cherry-picker idea was what you'd have to do, but you'd be hacking off the top (afore mentioned 'crape murder') and it' would bush out in a very unattractive fashion.

Look for a single stemmed tree, and just do your research. Figure it will grow to its max possible size to be on the safe side. CMs grow 2-3' a year.

These are lovely trees.
Christine

Okay, we've changed plans... and thank you to everyone helping to keep me grounded (though renting a cherry picker could be such fun!). Still want crape myrtles, but given our situation and desires--like privacy from street and buffer from sound--I realize as much as I love crape myrtles, a row of them will not give us that much of the year (still not one leaf on the one in my neighborhood). Then there are the growth and overhang issues as well. So we are now considering removing all the juniper from the slope, planting a row of narrow arborvitae as an evergreen fence along the street and using 2 or 3 smaller variety crape myrtles in the new landscaping on our side. That way they'll be able to drape naturally, and we'll still enjoy their blooms in summer and not sweat their nakedness in other seasons.

Are there lavender varieties that get much fall color?

Zuni- 9 to 12 high and red-orange in the fall, well, you can research the details, and I just put mine in so I can't say yet how it really looks, but I have high hopes.