I looked into a bit and can't seem to determine any issues. Should I post a pic of a leaf up close? I thought some of the little brown spots where frost damage. There were several nights of 30 degrees when it had already leafed out.

Powdery Mildew maybe? Rhonda

Vincas and portulacas love hot and dry so they have nothing to whine about! However, if the rose and hydrangea are happy in that area, it should be getting adequate moisture. Lilacs, though, can be finicky in our heat. In other words, if it was 85 degrees with the same exact moisture, they'd probably be profoundly happy. At 95 or higher, though, they just need more. I liked Annie's idea of rigging up something for shade--even a bedsheet draped over them during the hottest part of the day. (No plastic of any kind though, and esp. not touching the foliage.) If the surrounding plants are not moisture stressed, then I am more inclined than ever to think it is transplant shock. People are always surprised to learn that transplant stress can show up even a year or more after transplanting. However, remember that with trees and shrubs, and even a few of the larger herbaceous pernnials, the plant can often "operate" for a year or so on stored energy. So, if it got too dry during the summer after it was transplanted, it might not have shown too much shock because it could "operate" off stored energy. Now, quite some time later, the stored energy is gone and the lilac is saying "Hey, I was stressed and I'm showing it now." It doesn't seem possible, but it does happen. We have acres and acres of trees and they survive only on rainfall. If we have a severe drought, their leaves may turn yellow, brown and orange, and may even drop, and you think the tree is dead. But it is not--only going dormant in order to survive. THEN, in the spring, they leaf out and you think they are fine. Right? Wrong. After a few weeks or months, often some of them start going downhill and die....and it is because of the previous year's drought, not anything current. It happens a lot, but (thankfully) more often with SWTT (soft-wooded trash trees) or SWFGTT (soft-wooded fast-growing trash trees). I hardly ever see it with established, high quality trees like oaks. So, it is probably either heat stress or delayed syptoms of last year's transplant shock. Either way, it shouldn't be fatal. Dawn

please see link on proper planting ... which includes planting in april .. not june ... the plant had little time.. to settle in before summer heat and drought ... watering should be deep and infrequent.. with near drying in between such ... insert finger to 3 inches.. and find out when it needs water ... no spraying the leaves .. i never water my 15 year old Ls .. and in severe heat and drought.. they droop every afternoon .. and recover every night ... presume your stock comes disease free .. i have grown Ls for 4 decades.. and never did anything to them other than water them the first year ... do not spray it .. do not cut stuff off it ... on some level.. i fear you may have tried to love it to death ... these are what i call .. run it over with the truck plants .... they simply shouldnt be problematic ... but for a large plant.. improperly planted ... good luck .. ken https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub