Hi. I want to prune this lilac that is growing into my yard and taking up too much footprint. I’d like it to be tall for privacy but not take up so much yard.
Its also leaning towards south and was wondering if I could stake it to straighten?
Thank you for contacting the Toronto Master Gardeners about your lilac (Syringa vulgaris). Lilacs generally don’t require pruning for the first three or four years, but after that they really benefit from annual pruning, at least to remove any dead and diseased wood and to open up the interior of the shrub to more light and air. The best time to prune a lilac is just after it has flowered because once the blooms fade, lilacs set the buds for next year pretty quickly. So pruning after the new buds have appeared will result in fewer flowers next year. I think your choices at this point are to prune in the late winter (and have fewer flowers a couple of months later), or wait until next year’s flowers have just finished and prune then. Do not prune in the fall because pruning triggers new growth which will likely die off since there will be insufficient time for it to harden before the first frost.
S. vulgaris typically grows to 12-16’ in height and 8-12′ in width, so they definitely take up more space as they mature. You will likely need to do more than minimal pruning each year to contain it within your desired space.
Here is a link to an excellent You Tube video on pruning lilacs.
Regarding straightening you lilac, there are several factors to consider. Most important is to understand why it is leaning, because without addressing the cause it is likely that your shrub will resume leaning when the stakes are removed. (Staking should be considered a temporary not permanent solution. Your shrub will grow stronger roots and stems when it has some flexibility.) Leaning could be caused by a number of things, but looking at your picture I think that while your shrub looks pretty healthy it is not getting enough light. It looks like your lilac is planted too close to the fence behind it so the whole plant is leaning away from the fence as it looks for more room to grow and as it tries to get more light inside and on all sides of the plant. I can’t see the far (west) side of your plant, but it also looks like that huge tree in the background of your picture might be blocking light from your lilac in the afternoon. Lilacs need at least six hours of full sun daily to be at their best,
I think it would probably be best to straighten your lilac before staking, by loosening the soil around it so that the root position can be adjusted. I also think it would be best if each of the main stems is staked. I suggest getting professional help for this, for advice on whether staking is a good approach for straightening your shrub and if it is even feasible, or are there other options. Landscape Ontario is a good source to find a landscape contractor.
I think it’s possible to keep your lilac where it is, and manage its shape and growth with good pruning every year, and perhaps settle for less than ideal flowering (although it will not be happy at all in a shady spot). However, all things considered, it could be that your lilac is not ‘the right plant in the right place’. So another option for your consideration would be to transplant your lilac to spot in your garden that has full sun and lots of space for growth so it can thrive, and replace it with a tree or shrub that is better suited to your lilac’s current location. We would be happy to suggest alternative plants if you would like to submit another question with at least a general idea of what you’re looking for and a detailed description of the planting site including surrounding plants, what type of soil is there (clay, sand, loam) and what is behind your lilac which I can’t see clearly in your current photo.
All the best with your lilac!