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I want to plant a lilac hedge. I've never done lilacs before - how far apart should I plant them? Can I do a double row for a thicker hedge? If so, how far apart should the rows be? How fast do they grow? Do they need special care (they will be pretty close to a fairly busy road)? Can I plant them now, or should I wait until it's a little warmer? What are their fertilizer and water requirements? Will they be useful as a bit of a wind- and soundbreak? Thank you.

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This is in answer to your question about growing lilacs:  Lilacs are a good choice in our area for a beautiful hedge but they need good air circulation and 6 to 8 hours of full sun each day for good bloom production, so I would not plant a double row. Plant a single row with each plant about 3 to 6 feet apart to result in a 6- to 8-foot tall hedge. Bareroot shrubs should be planted when dormant (in late fall or early spring), but if you get your plants in containers, the timing is not so critical because they will have a fairly well developed root system for uptake of water. 

There are hundreds of varieties of lilacs. I will assume you are talking about the common lilac (Syringa vulgaris), in which case you can expect a moderate rate of growth of up to 1 foot per year. Lilacs need well-drained soil, so if your soil is clayey, you can amend your soil with peat moss to a depth of 6 inches prior to planting to improve soil drainage.  You need not add fertilizer at the time of planting if you have good organic soil.  If not, add a slow release granular fertilizer (5-10-5) or (5-10-10) about one month after planting and water it in well. Also, mulch around the base of your plants with shredded bark or wood chips to keep roots cool, preventing evaporation of soil moisture, and reduce weeds. 

You should water your plants deeply about once a week after planting to encourage good root growth.  Once established, your lilacs will require only occasional deep watering.  Lilacs produce flowers on last year's growth, so wait until just after their blooms fade to prune.  Prune out old canes at their base to allow greater access to light and to keep your plants healthy and vigorous.  You don't need to remove spent flowers after bloom, and never "top" your lilac -- this produces fast, unsightly growth that will ruin the natural shape of your plant.

Lilacs can make a lovely and fragrant wind and sound barrier.

For more information, check out the "Growing lilacs" fact sheet at
http://extension.usu.edu/files/publications/publication/pub__8037226.pdf

Posted on 23 Apr 2008

Heidi Kratsch
Ornamental Horticulture Specialist

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