Pruning lilacs

Discussion in 'Woody Plants' started by lavalos, Jul 19, 2008.

  1. lavalos

    lavalos Active Member

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    I have two lilacs that didn't bloom this year. It was my first spring in this house so I don't know what happened before. I wanted to prune it to rejuvenate it, but know that pruning too late will damage next years bloom. Is it still good time for pruning?
     
  2. Michael F

    Michael F Paragon of Plants Forums Moderator 10 Years

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    Lilacs are best pruned with paper scissors, and should only be pruned on 30th February.

    The longer one is left with no pruning at all, the more it will flower. If pruned, it can be up to 7 years till they flower again.
     
  3. jeanneaxler

    jeanneaxler Active Member

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    Lilacs are best pruned with paper scissors, and should only be pruned on 30th February.

    A wild guess: you don't think lilacs should be pruned.
     
  4. Michael F

    Michael F Paragon of Plants Forums Moderator 10 Years

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    How did you guess!! ;-)
     
  5. lily

    lily Active Member 10 Years

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    Darn, I pruned mine on Feb. 29th. lol
    Actually, I pruned mine sometime in Jan/Feb. I had lots of blooms this year but I would like to have seen more leaves.
     
  6. Ron B

    Ron B Paragon of Plants 10 Years

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    It can take more than one year for lilac stems to grow large enough to resume flowering. The value of cutting yours back depends on why they did not bloom. Usually the canes that would be selected for hard pruning, down to a short length - at the end of winter - would be ones that had become old and twiggy. These would ordinarily still be producing flowers, as would the more vigorous portions. If the bushes have grown for years without severe pruning and are large enough to bloom, then there is some other kind of problem preventing flowering.

    Someone could also accidentally prevent flowering just by pruning back all the tips lightly. Lilacs bloom only on the ends of branches, as do rhododendrons. The way new shoots come from right below the flowerheads is also similar. These will produce next year's flowers, if damaged or removed then no flowers from these next year.
     
  7. lily

    lily Active Member 10 Years

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    Ron,
    How can you tell the difference between a branch or a sucker on a lilac tree? I don't want to make the mistake in cutting off a branch thinking it is a sucker. Thanks again for your help.
     
  8. Michael F

    Michael F Paragon of Plants Forums Moderator 10 Years

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    There's no real difference, except for age. A sucker grows into a new branch. Leave it long enough (5-7 years or so) and it'll become mature enough to start flowering.

    The most floriferous lilacs I've seen have all never been pruned at all. A good old (over 50 years old) unpruned specimen in flower is such a solid mass of flowers you can hardly see the leaves.
     
  9. growing4it

    growing4it Active Member 10 Years

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    Lilacs has always beena mystery to me. I had thought there was a winter chilling requirement.

    So, if I understand correctly, lilacs need to be 'mature' to flower and they flower on new wood, near the tips. If the lilac is pruned and the new tips are removed, it could take years to flower again?
     
  10. lavalos

    lavalos Active Member

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    Looking for other reasons why the shrubs don't flower, I can say that one of the shrubs is between two spruces, so there is not to much sun on it. On top of that , I believe that spruces and pines acidify the soil so probably the soil is two acidic for blooming. Finally, last year the shrubs had what I think was powdery mildew, and I don't know if this could damage the plant.
     
  11. C8luvs2gardn

    C8luvs2gardn Active Member

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    Lavalos, I have a situation with Lilacs which is very similar to yours. I have a HUGE maple tree on my front lawn, which faces west. In the morning the front is in shade, and when the sun moves around the tree shades pretty much the whole front so the lilacs don't get much direct sun. There is also a big problem with air circulation. There are two lilacs, one at each corner of the porch. When I bought the house in 2003 they were already there and about 12' tall. The space between them was taken up by some really ugly never-pruned half-dead yew shrubs. In 2003 and again in 2004 I pruned them at the base to get rid of all the little runners including the root system (at least as much of them as I could get) and a lot of the suckers which I hoped would permit better air circulation. Didn't work. I had powdery mildew every summer.

    As much as I love lilacs these ones are definitely not happy, so in 2005 I cut the right-hand one (see pic) back to about 2' (mainly because I didn't have any tools big enough to finish the job)and in 2006 I did the same to the left one. I removed all the runners and trimmed back the roots severely (got rid of the ugly yew shrubs too). As you can see this year both lilacs have healthy leaves and seem to be thriving. I will have to trim the right-hand one again as it is now about 10' and I have just noticed that the top branches are getting mildew again. They are also starting to get spindly - a sure sign of not enough light.

    I have a second problem which is related to the root system of the lilacs. There is a runner which has sprouted up right through my Alchemella mollis (see pic below), and I would very much like to get it out. My plan is to dig about a foot away from A.mollis and sever the runner from the parent and then (hopefully) remove it without causing too much trauma to the Alchemilla.

    I'm attaching a few pictures:
    1. late March 2003, the 'before' picture.
    2. shows the yew removed, the lilac on the right was cut back severely in 2005 and the one on the left had previously only been pruned at the bottom.
    3. taken about a week ago around 5:30 pm and as you can see mostly deep shade.
    4. as you can see the runner has sprouted right up the middle of the ladys' mantle.

    If anyone has any ideas or suggestions I'd appreciate the feedback - should I keep these shrubs, pull them out, keep them small, and especially what to do to save the Alchemilla?

    thanks,
    Cate
     

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