Rule of thumb is what blooms in the Spring, plant in the Fall and what blooms in the Fall, plant in the Spring. I have had luck in transplanting bushes outside the rule of thumb as long as a lot of the dirt was left around the root system and watered well after planting. If your lilac start is tiny and no soil around the root, I'd dip it in root hormone, plant in a pot, set it outdoors and bring indoors over the winter and plant next Spring.
Add your voice to the conversation. Click here to answer this question.