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Tall lilac bushes with few leaves and flowers #813239

Asked October 05, 2022, 10:13 AM EDT

My two 5+ year old lilac bushes aren't bushy. They give few if any flowers. This fall I trimmed the dead and removed a couple branches at the base, for the first time. But it seems like I should cut some of the remaining long limbs in half to encourage growth where cut. But nothing I've seen indicates doing that. What should I do next? Should I remove grass and replace with mulch? No grass fertilizer has been used in the area for a couple years, in case that was the flowering problem.

Hennepin County Minnesota

Expert Response

Lilacs need full sun (6+ hours) and well drained soil to support healthy shrubs. It appears you have large trees nearby that could be shading them. If this is correct they will keep reaching for sun and not produce many blooms. Lilacs bloom on old wood. Any deadheading of blooms should take place immediately after bloom decline. If pruning occurs later there will not be blooms the next year. Lastly, if the shrubs are receiving adequate sun and timely pruning I would recommend a soil test. It could be that there are not adequate nutrients to support a healthy shrub. The link below has information on growing lilacs as well as information on soil testing. 

https://extension.umn.edu/trees-and-shrubs/lilacs
Amy J. Extension Master Gardener - HC Replied October 05, 2022, 9:51 PM EDT
This spring after pruning 1/3 of lilac bush on both bushes, both showed flowers this year. The one closest to the sun seems to be providing new shoots.  The one further away from light isn't giving any new shoots. Think I see some other plant with slightly different leaf pattern emerging. 

Should I try to move this 12 foot lanky lilac bush?  Or trim another third off and see what happens. Can I propagate with the stems?

It is next to a really dense lilac bush that I have never trimmed or thinned.  It's at least 30 years old.  Should I try to thin it out, allowing more light to the lanky  lilac?



On Wed, Oct 5, 2022, 8:51 PM Ask Extension <<personal data hidden>> wrote:
The Question Asker Replied June 04, 2023, 10:30 PM EDT
In your photos I see two lilacs that are pretty sparse next to a large Euonymus (burning bush). Both lilacs appear minimally leafed out and leggy, likely due to not getting 6+ hours of sun/day. You could certainly try pruning them down by 1/3 to see if it results in additional growth and bloom. It should be done now as all blooming occurs on old wood (growth from this summer).  
Amy J. Extension Master Gardener - HC Replied June 05, 2023, 3:40 PM EDT

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