Q. My lilacs have bloomed and the flowers are gone. Is now the time to prune or do nothing? How do you prune or care for the lilacs.
|Lilac planted in rock mulch with brown scorched leaves|
A. Most people don't know that low-chill varieties of common lilac will grow here as well as the Persian lilacs. Plant them in plenty of sunlight but in places which avoid the hot afternoon sun. All lilacs must be planted in a composted soil with a wood chip mulch. Rock mulch will not work.
Low-chill varieties do not need as much low temperatures to produce flowers. Lilacs that are not low chill will not produce as many flowers in our warm winter climate. Some plants require long periods of time when temperatures are cold so that flowers will be produced the next year.
Persian lilac may be a better choice for our climate and in smaller yards than common lilac. Persian lilacs are smaller in stature than common lilac, with smaller flower clusters and a lower winter chill requirement.
Hopefully local nurseries and garden centers that sell lilacs for our climate are selecting low-chill types such as an old time favorite here called "Lavender Lady". I believe this, along with "Angel White" were the first low chill lilacs available that would grow in the desert Southwest. Many of these low-chill varieties are referred to as the “Descanso Hybrids”.
Lilacs are not desert plants so they require lots of compost mixed in the soil at the time of planting with the soil covered in wood chips that decay over time. They should not be in rock mulch.
A very nice article appeared in Sunset Magazine and you can read it here http://www.sunset.com/garden/flowers-plants/mild-climate-lilacs
As with any seasonal flowering shrub or tree the best time to prune them is soon after flowering. If pruned later than this, the flowers for next year may not be produced.
First, remove the dead flowers before they form seeds by cutting them off at the base. Next, if needed, cut back branches or stems.
To increase the number of flowers you should increase the number of new branches it produces. Use a "heading cut". This type of cut is made somewhere along the length of the branch, usually just above a leaf on the outside of the branch.
Heading cuts grow three or four new shoots for every one that is cut that is made. This is an excellent way to make a shrub denser with more flowers.
If the shrub is getting too large, remove one third of all the longest stems back to within a couple of inches above ground. New stems will grow from just below these cuts.
A radical way of pruning this plant is to totally cut it off just above the soil surface. With plenty of water and some fertilizer new shoots will grow from these very short stubs resulting in an all-new plant. This is pretty radical but if the plant is overgrown with lots of wood showing, this may be your only alternative.
Remember, after pruning give it plenty of water and fertilize it with an all-purpose fertilizer.