Q: I have a lilac bush, which I purchased from a mail order company. It is about 12 years old, and it has never bloomed a single flower.ย It grows larger each year and has lush green foliage. I have given it fertilizer but nothing seems to help. What am I doing wrong?
A: The common lilac (Syringa vulgaris) is a favorite in many places so I understand your desire to grow them. Unfortunately, your place might not be suitable. Lack of blooms is usually related to one of six causes: the age of the plant, temperature, alternate flowering, light, nutrition, or pruning practices. In your situation, I think the likely problem is temperature. Lilacs require a certain amount of cold to trigger blooming, also known as vernalization. We don’t usually get enough cold in Southern Arizona for this plant to bloom unless you live at higher elevations. There are lilacs at the Santa Rita Experimental Range near Green Valley than have been monitored for bloom times by the USA National Phenology Network for many years. The elevation there is approximately 3,714 feet above sea level. You can check their web site for details if you are interested: usanpn.org/nn/lilacs
In downtown Tucson, where the elevation is closer to 2,389 and winter is barely recognizable, itโs too warm.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to
