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I have a very old (about 120-125 yrs. old) lilac bush. It was cut almost to the ground 20 years ago. I had been told that this was how to control giant lilacs. It had formerly been 18' high and 25' across, and was hard to mow under. I regret this step, and the bush has never looked good since. The spruce tree behind it has really grown, and the lilac is growing at an angle, with thin, spindly stems.

  • The shrub is on foundation soil from the house
  • It gets full sun from noon to about 7 pm
  • I fertilize with compost and Spray-n-Grow Perfect Blend
  • I don't water it, but the soil stays moist most of the year
  • I've treated for hornets in the past when they were an issue chewing bark
  • Most of the growth is root suckers-the old stumps are mostly rotted out

I like to keep as many 'historic' plants as possible on my property. Assuming I want this one to live and recover, what should I be doing to maintain it, or keep it from going downhill? enter image description hereenter image description here

2 Answers 2

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Tough one - for one thing, it may not even be the original lilac, it depends on whether the tree was grafted or not. Rootstock used in 1950 would most likely have been privet or syringia vulgaris - if you never had sucker growth before you cut the tree down, and because the tree was so old, it's likely it was on syringia vulgaris rootstock. On the other hand, if you did get lots of suckers, then it was on its own roots, in which case, the regrowth is actually your original lilac. The trouble is, as you can see, growth does not generate from heartwood in such an old and thick trunk, so any regrowth will always be around the outer edges, either from the cambium layer or straight off the roots below. This obviously means you'll always have a bare circle in the centre, so the best you can hope for is a sort of dense shrub which might cover that area up.

In terms of appearance, and as you cut the thing down in the first place, you might want to consider killing it off and replanting another tree further along.

UPDATE in response to comment:

Killing it off was just a suggestion and yes you can keep it, as I said previously, but only by growing it as a shrub, and it may never be particularly bushy or attractive, whatever you do. You're already doing everything you can, but I wouldn't let those shoots develop into individual trees, which they might try to do if left long enough, that'd be really ugly. Although one person's 'ugly' is another's delight, I suppose.

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  • This was a large, suckering shrub with many large trunks. I believe it is the species lilac, Syringia vulgaris and was not grafted.
    – J. Musser
    Commented Jun 17, 2014 at 19:42
  • Also, I want to know if there is a way to save it (ie, not killing it off).
    – J. Musser
    Commented Jun 17, 2014 at 19:43
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    What's wrong with it? Gee, it looks very happy/healthy.
    – stormy
    Commented Jun 17, 2014 at 22:18
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    Besides improving the soil with life I'd get the pH up to 6.5. 6.0 in my experience is too acidic for lilacs. Try to do small raises over time. Anywhere between 6.5 and 7.0 you should see a difference. Try finding horsetail, dry it, pulverize it in your cuzinart and spread under compost or in the compost. Silicon really helps plants do whatever...grin.
    – stormy
    Commented Jun 19, 2014 at 21:07
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    @stormy BTW, you forgot to ping me again. Just found this now. :) I'll lime and add a layer of compost before I mulch. Thanks for the input.
    – J. Musser
    Commented Aug 5, 2014 at 1:42
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Here are 3 ideas on pruning, with the outermost shape an example of conservative tipping. The more pruning, the more the shrub itches to branch at lower levels and to sucker from the gound.

3 ideas on pruning

The lilac may well be leaning away from the spruce for more light. No law against tipping every few years.

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