I overwinter a number of them in my converted garage every year. I don't heat it, so it ranges between about 40 to about 50, surviving on air circulation from the heated house it's attached to. Mine always break dormancy in March. There is moderate to low light out there, and the new growth is extremely weak and stringy and tender. I chuck them outside by mid April. The new growth either wind and sun burns off or is killed by frost/freezes. It doesn't matter an iota. They are such rampant, vigorous growers they sprout right back. And, of course, they bloom on NEW WOOD, so you want a lot of new growth. If you just keep it cool, give it moderate to bright light, keep it watered just enough to keep it from drooping, and then pop it outside after danger of severe cold is over (shelter it if its going to drop below 30 at night), it will be just fine. Oh, I have some in-ground CM's as well. They've been in close to 10 years now. They function as dieback perennials here, coming up from the root system. They bloom once in a while, many years only getting to the bud stage when fall frosts take them. The last couple of years, with the hotter summers, I actually had good floral displays on them in late summer/early autumn. They generally get to about 4 feet tall. Even in the years they don't bloom, the somewhat glossy foliage is attractive. Mine are sited in the open, if I had a nice, southern exposure brick or stone wall where they could bake in the sun and heat, I'm sure I'd get more blooms in that kind of favorable micro-climate, but alas, my walls are all grey-white vinyl siding, and I have large shade trees on the southern exposure side of the house.

I realize I am about 9 years too late, and I don't know whether you've already tried growing crape myrtles, but just came across your question. I am a transplant from Texas currently living in the Indy area (zone 6) and missed my crape myrtles more than any other tree/shrub. I doubt you'll ever be able to grow a tree, but I have been successfully growing several varieties in the ground since 2013, even with below zero temps we had this past winter. I did lose a few early on, but once established, they have done very well, even during drought conditions. You MUST have full sun, and southern exposure is best. I wouldn't bother with eastern or northern exposure. I The key to getting them to come back every year is to cut back to about 8-10 inches in fall after blooming then mulch the heck out of them (at least 6 inches) Around mid April, I pull back the mulch and let sun get to the root area. You may not see any sign of growth return until May or June, especially the first few years, but one day you'll check on them and be excited to see leaves sprouting. Once that happens, they grow quickly. Mine start blooming late June to early July. Other than that, they are very low maintenance. The only watering they get is when it rains, and I've never had a problem with insects or diseases. Bees love them. I forget to fertilize, yet they still bloom profusely. Three of the varieties I grow are supposedly miniatures (Mardi Gras, New Orleans, & Cordon Bleu), but they get pretty big by the end of the summer. I also grow a shrub type Purple Velvet which grows to 3-4 feet tall each year. I purchased them at https://www.crapemyrtle.com/store/c2/Miniature_Crape_Myrtles.html They are a little pricey, but worth it, in my opinion. You can call customer service to see what they say about growing in zone 5. If nothing else, you can grow one in a pot and bring it inside, but that's more work than I want to deal with. Follow planting instructions for best success. Hope you find this helpful, and I wish you great success. ️

I have a sister in Cincinnati that has a white CM. I am sorry that we do not know more about it, but it is very happy there in her back yard. It gets full sun for most of the day and tolerates drought. It has been a very dry year there but the CM has been in full bloom and looking lovely! I am in NWPA and plan on trying one here.

I have a smaller crape of adifferent variety than Tonto and it is under 4 feet and does fine, but the blooms are not as dramatic as this particular plant. It gets about 6 to 7 feet tall and is about 18 inches at the base and about 4 feet wide at the top. To stake it would most likely take some type of center support due to the weight. Not sure how to drive a stake through the center of its roots though. If I can keep my husband from digging it out, I'll try something next year as a last ditch effort. We have not fertlized it at all other than when originally amending the soli when initially planted about 4 years ago and it is in a place will relatively poor, clay soil.