Eastern Lilacs

Question from Rod:
I live in an area east of Jamul Ca. I.m at 2500ft. I’ve had lilacs (lavender)since I’ve lived here (“72″) they were here before that.They always bloom but something that has never happen before. Their blooming now in the middle of oct. Not abunduntly but several blooms on all the plants. I keep them watered as usual and not doing anything different. Also they along with everything else was burned to the ground in oct.”07”. They came back from the roots and have bloomed since. This is a first for this oct. thing. Any ideas? Thanks.

Answer from Pat:
When a plant blooms out of season this bloom is called a “sport”, a term which is used as a noun or a verb. The reason for fall bloom to sport on lilac, a spring-blooming plant, is unusual weather temperatures especially at night. When there is a cool summer with cold nights perhaps lasting into fall and then these cool temperatures are followed by warm temperatures, the plant thinks it went through a cold winter and and a few of the buds already in existence will pop open. The flower buds are already there and if the plant has been chilled and then is warmed up it thinks winter is over and now it’s spring so it will bloom.You can remove the sporting blooms after they fade, but don’t cut back too far. Cutting lilac back now will remove buds that should bloom next spring. There is probably not enough time for the stems that bloomed in fall to set more buds for spring bloom.

I am glad to hear your lilacs did not bloom massively but simply sported a few blooms. This means you will still have many flower buds left in place for spring bloom. Any spring-blooming plant that sports bloom in fall will bloom again in spring as long as some flower buds remain in place.

Fall bloom on plants that bloom once a year in spring is not uncommon in Mediterranean climates. I had a similar experience last fall and this spring with my yellow Lady Banks rose (Rosa banksiae ‘Lutea’). Lady Banks rose sets its flower buds in late summer and early fall and it blooms in spring. If you cut back too late in the year you lose all the bloom. (People who prune lilac in summer or fall lose all the bloom also.) Lady Banks blooms on the wood that grew during the summer right after bloom. Thus by fall the flower buds are there, and they stay on during our mild winter. A year ago, however, my Lady Banks rose bloomed massively in fall and then bloomed again in spring but not quite as massively as usual. It has never bloomed heavily in fall before, though it often sports a few fall blooms. The heavy bloom in fall was caused by the swing from cold temperatures and fog in late summer and fall followed by a warm snap with lots of sunshine. The rose thought spring had arrived and burst into bloom months ahead of schedule.